Reference 600 Potentiostat/Galvanostat/ZRA Operator`s Manual

Reference 600   Potentiostat/Galvanostat/ZRA Operator`s Manual
Reference 600

Potentiostat/Galvanostat/ZRA
Operator's Manual
Copyright 2011 Gamry Instruments, Inc.
Revision 5.7
February 28, 2011
If You Have Problems
Contact Gamry Instruments at your earliest convenience. We can be contacted via:
Telephone
(215) 682-9330 8:30 AM - 6:00 PM US Eastern Standard Time
Fax
(215) 682-9331
Email
[email protected]
Mail
Gamry Instruments, Inc.
734 Louis Drive
Warminster, PA 18974
USA
If you write or fax us about a problem, provide as much information as possible.
If you have problems in installation or use of a system containing a Reference 600, it would be helpful if
you called from a phone next to your computer, where you can type and read the screen while talking to
us.
We will be happy to provide a reasonable level of free support for registered users of the Reference 600
Potentiostat/Galvanostat/ZRA. Reasonable support includes telephone assistance covering the normal
installation, use and simple customization of a computerized system containing a Reference 600 connected
to a Windows compatible computer hardware.
A service contract that extends both the hardware warranty and software update period is available at an
additional charge. Software updates do not include software enhancements offered to our customers at
additional cost.
Enhancements to the Reference 600 and Gamry’s standard applications software that require significant
engineering time on our part can be performed on a contract basis. Contact us with your requirements.
i
Limited Warranty
Gamry Instruments, Inc. warrants to the original user of this product that it shall be free of defects resulting
from faulty manufacture of the product or its components for a period of two years from the original
shipment date of your purchase.
Gamry Instruments, Inc. makes no warranties regarding either the satisfactory performance of the
Reference 600 Potentiostat/Galvanostat/ZRA including the software provided with this product or the fitness
of the product for any particular purpose. The remedy for breach of this Limited Warranty shall be limited
solely to repair or replacement, as determined by Gamry Instruments, Inc., and shall not include other
damages.
Gamry Instruments, Inc. reserves the right to make revisions to the system at any time without incurring any
obligation to install same on systems previously purchased. All system specifications are subject to change
without notice.
There are no warranties which extend beyond the description herein. This warranty is in lieu of, and
excludes any and all other warranties or representations, expressed, implied or statutory, including
merchantability and fitness, as well as any and all other obligations or liabilities of Gamry
Instruments, Inc; including but not limited to, special or consequential damages.
This Limited Warranty gives you specific legal rights and you may have others, which vary from state to
state. Some states do not allow for the exclusion of incidental or consequential damages.
No person, firm or corporation is authorized to assume for Gamry Instruments, Inc., any additional
obligation or liability not expressly provided herein except in writing duly executed by an officer of Gamry
Instruments, Inc.
ii
Disclaimers
Gamry Instruments, Inc. cannot guarantee that the Reference 600 Potentiostat/Galvanostat/ZRA will work
with all computer systems, operating systems, and third party software applications hardware/software.
The information in this manual has been carefully checked and is believed to be accurate as of the time of
printing. However, Gamry Instruments, Inc. assumes no responsibility for errors that might appear.
Copyrights
Reference 600 Potentiostat/Galvanostat/ZRA Operator's Manual copyright 2007-2011, Gamry Instruments, Inc., all rights reserved.
Gamry Framework - copyright 1989-2011, Gamry Instruments, Inc., all rights reserved.
Reference 600, PC4, PCI4, ECM8, Gamry Framework, DC105, EIS300, and Gamry are
trademarks of Gamry Instruments, Inc.
No part of this document may be copied or reproduced in any form without the prior written consent of
Gamry Instruments, Inc.
iii
Table of Contents
If You Have Problems ....................................................................................................................i
Limited Warranty...........................................................................................................................ii
Disclaimers ....................................................................................................................................iii
Copyrights .....................................................................................................................................iii
Chapter 1 -- Safety Considerations ................................................................................................1-1
Inspection.........................................................................................................................1-1
Product Safety ..................................................................................................................1-1
AC Mains Connection to the Power Brick ..........................................................................1-2
Grounding in the Reference 600 .......................................................................................1-2
Temperature and Ventilation.............................................................................................1-3
Defects and Abnormal Stresses..........................................................................................1-3
Environmental Limits.........................................................................................................1-4
Cleaning ...........................................................................................................................1-4
Service .............................................................................................................................1-4
RFI Warning .....................................................................................................................1-4
Electrical Transient Sensitivity ............................................................................................1-5
CE Compliance .................................................................................................................1-5
RoHS Compliance ............................................................................................................1-5
Chapter 2 -- Introduction ..............................................................................................................2-1
About this Manual ............................................................................................................2-1
About the Reference 600 ..................................................................................................2-1
Notational Conventions.....................................................................................................2-2
Chapter 3 -- Instrument Circuitry ..................................................................................................3-1
Reference 600 Schematic/Block Diagrams .........................................................................3-1
Chapter 4 -- Installation ................................................................................................................4-1
Initial Visual Inspection .....................................................................................................4-2
Physical Location ..............................................................................................................4-2
Computer Requirements ...................................................................................................4-2
Plug & Play System Configuration......................................................................................4-3
Power Cord and Power Connection ..................................................................................4-4
Power Up Test..................................................................................................................4-5
USB Cabling .....................................................................................................................4-5
Front Panel USB LED ........................................................................................................4-6
1st Time Device Installation in Windows ............................................................................4-6
Multiple Potentiostat Systems ............................................................................................4-9
Cell Cable Installation .......................................................................................................4-9
Device Manager ...............................................................................................................4-9
Authorization Codes and Label .........................................................................................4-10
Firmware Update..............................................................................................................4-11
Application Software Installation and System Checkout......................................................4-13
Calibration........................................................................................................................4-13
Separate Calibration for Each Reference 600 Cable Type......................................4-13
DC and AC Calibration ........................................................................................4-13
Low I Range DC Calibration.................................................................................4-14
Chapter 5 -- Cell Connections .......................................................................................................5-1
Normal Cell Connections ..................................................................................................5-1
ZRA Mode Cell Connections .............................................................................................5-2
Membrane Cell Connections .............................................................................................5-3
Chapter 6 -- Panel Indicators and Connectors................................................................................6-1
Front Panel .......................................................................................................................6-1
Cell Connector.....................................................................................................6-1
The Power LED....................................................................................................6-1
The USB LED.......................................................................................................6-1
Cell LED ..............................................................................................................6-2
Overload LED ......................................................................................................6-2
Rear Panel ........................................................................................................................6-3
Power In Jack.......................................................................................................6-3
Power Switch.......................................................................................................6-3
Chassis Ground....................................................................................................6-4
USB Port..............................................................................................................6-4
Thermocouple Input ............................................................................................6-4
Misc I/O Connector .............................................................................................6-5
I Monitor BNC .....................................................................................................6-5
E Monitor BNC ....................................................................................................6-6
Ext. Sig. In BNC ...................................................................................................6-6
Sig Gen Out BNC ................................................................................................6-6
Aux In BNC .........................................................................................................6-7
Chapter 7 -- Stability in Potentiostat Mode ....................................................................................7-1
Capacitive Cells and Stability.............................................................................................7-1
Improving Potentiostat Stability .........................................................................................7-2
Chapter 8 -- Measurement of Small Signals....................................................................................8-1
Overview..........................................................................................................................8-1
Measurement System Model and Physical Limitations........................................................8-1
Johnson Noise in Zcell .........................................................................................8-2
Finite Input Capacitance ......................................................................................8-3
Leakage Currents and Input Impedance................................................................8-3
Voltage Noise and DC Measurements ..................................................................8-4
Shunt Resistance and Capacitance........................................................................8-5
Hints for System and Cell Design.......................................................................................8-5
Faraday Shield .....................................................................................................8-5
Avoid External Noise Sources ...............................................................................8-6
Cell Cable Length and Construction......................................................................8-6
Lead Placement ...................................................................................................8-6
Cell Construction .................................................................................................8-7
Reference Electrode .............................................................................................8-7
Instrument Settings...............................................................................................8-7
EIS Speed ............................................................................................................8-7
Ancillary Apparatus ..............................................................................................8-7
Floating Operation ............................................................................................................8-8
Appendix A -- Reference 600 Specifications ...................................................................................9-1
Appendix B -- Reference 600 Cell Connector .................................................................................10-1
Appendix C -- Misc I/O Connector .................................................................................................11-1
Appendix D -- Auxiliary A/D Input Characteristics...........................................................................12-1
Jumper Identification ........................................................................................................12-1
Input Impedance Selection................................................................................................12-2
Bandwidth Selection .........................................................................................................12-3
Aux A/D Specifications ......................................................................................................12-3
Function Call to Set the Aux A/D BNC Characteristics ........................................................12-3
Appendix E – CE Certificate............................................................................................................13-1
Declaration of Conformity.................................................................................................13-1
Certificate of Conformance ...............................................................................................13-2
Comprehensive Index ....................................................................................................................14-1
Chapter 1 -- Safety Considerations--Inspection
Chapter 1 -- Safety Considerations
Your Reference 600 Potentiostat/Galvanostat/ZRA has been supplied in a safe condition. This chapter of
the Reference 600 Operator's Manual contains some information and warnings that you must follow to
insure continued safe operation of the Reference 600.
Inspection
When you receive your Reference 600 Potentiostat/Galvanostat/ZRA you should inspect it for evidence of
shipping damage. If any damage is noted, please notify Gamry Instruments Inc. and the shipping carrier
immediately. Save the shipping container for possible inspection by the carrier.
WARNING
A Reference 600 that has been damaged in shipment can be a safety hazard. Do not
operate damaged apparatus until a qualified service technician has verified its safety.
Tag a damaged Reference 600 to indicate that it could be a safety hazard.
Product Safety
The Reference 600 has been designed, tested and certified to meet the requirements of EN 61010, Safety
requirements for electrical equipment for measurement, control, and laboratory use. As defined in this
standard, it is a Category I apparatus, designed for connection to circuits other than the power mains.
The Reference 600 contains a limited amount of internal circuitry that is at “hazardous live” voltages as
defined in EN 61010 (the standard mentioned above). “Reinforced insulation” (again defined in EN
61010) is used to reduce the risk of electrical shock due to this “hazardous live” voltage.
The majority of the Reference 600’s circuitry does not contain voltages higher than 30 Volts DC. As a
generalization, input and output voltages in the Reference 600 are limited to 24 volts. This voltage level is
considered safe.
The “AC Adapter” supplied with the Reference 600 is certified under EN 60950. The AC Adapter converts
the AC mains voltage to 24 volts DC, which is used to power the Reference 600.
You should always use the AC adapter (power brick) supplied with your Reference 600 to supply DC power
to the instrument.
Warning
Do not use a DC power source other than the AC adapter model provided with your
Reference 600. Other replacements may void the performance and/or safety
characteristics of the Reference 600.
1-1
Chapter 1 -- Safety Considerations--AC Mains Connection to the Power Brick
AC Mains Connection to the Power Brick
The Reference 600 does not connect directly to an AC Mains supply. Instead, the mains are connected to
desktop AC adapter (power brick), which outputs 24 volts DC, which in turn powers the Reference 600.
NOTE
The Reference 600’s AC Adapter is rated for operation from 100 to 240 volts AC, 47
to 63 Hz. It should therefore be useful throughout the world.
The Reference 600 is normally provided with an AC line cord suitable for your location. This AC line cord
connects the AC mains to the AC power adapter. If your Reference 600 has been provided without an AC
line cord, or a cord that is not compatible with your local AC mains socket, obtain a line cord certified for
use in your country. Contact your local Gamry Representative or Email to [email protected] if you
are uncertain what AC line cord to use.
Grounding in the Reference 600
The circuitry and the metal case of the Reference 600 are not connected to an earth ground. If they were
connected to earth ground, it would compromise the Reference 600’s ability to make measurements in
electrochemical cells that contain earth grounded metal. A few examples of such cells include autoclaves,
metallographic stress apparatus, and detectors for capillary electrophoresis.
Most electrochemical cells are isolated from earth ground, so isolation of the Reference 600 from earth is
not required. In these cases, connection of the Reference 600 chassis to an earth ground may lower the
noise seen in an electrochemical test. A Chassis Ground binding post on the rear panel of the Reference
600 makes for easy implementation of this connection. Simply run a wire from this binding post to a
suitable source of earth ground. A black 1.2-meter wire is provided with the Reference 600 to facilitate
this connection.
NOTE
Sources of earth ground include;
•
Most metal water pipes,
•
the chassis of most electronic apparatus (which are generally earth
grounded), and
•
the protective ground terminal of an AC Mains power plug.
We recommend that you discuss grounding with an electrical or electronics
professional prior to making this earth ground connection.
Note this connection of the Reference 600 to an earth ground is not a “Protective Earth Ground” as defined
in EN 61010. The Reference 600 is safe in the absence of this connection.
This binding post is not intended for any use other than connecting the Reference 600 to an earth ground
to improve shielding against noise. Connecting this binding post to a hazardous voltage can create a
significant safety hazard.
WARNING
Do not connect the chassis ground binding post to any voltage other than earth
ground. An improper connection can create a safety hazard, which could result in
personal injury or death.
1-2
Chapter 1 -- Safety Considerations--Temperature and Ventilation
The Reference 600 contains spark gap surge suppressors that limit the voltage difference between the
Reference 600’s chassis ground and earth ground to about 90 volts. These surge suppressors are not part of
the safety mechanisms in the Reference 600. Instead they are present to limit the possibility of improper
instrument operation or instrument damage due to electrostatic discharge (static electricity) and other surge
events such as lightening.
Temperature and Ventilation
Your Reference 600 Potentiostat/Galvanostat/ZRA was designed for indoor use at ambient temperatures
between 0°C and 45°C.
The Reference 600 uses forced air-cooling to keep the components within the Reference 600 within their
recommended operating temperature range. Air is drawn into the Reference 600 chassis through slots
located on the sides of the chassis near the front panel. The air exits through the two fans at the rear of the
unit.
Caution
Do not block the airflow into or out of the Reference 600 chassis. While the circuitry
should suffer no damage due to excessive heat, the Reference 600 enclosure may
become uncomfortably hot to the touch if insufficient air flows through the chassis.
Running the Reference 600 without adequate cooling could shorten the time to failure
of some of the circuitry.
Be careful when operating the Reference 600 in an enclosed space (such as an enclosed relay rack or
NEMA enclosure). The temperature within the enclosure must not exceed 45°C. You may need to provide
ventilation holes or even forced air-cooling for the enclosed space if excessive temperature rise occurs.
Defects and Abnormal Stresses
You should treat your Reference 600 as potentially hazardous if any of the following is true of the unit:
•
it shows visible damage,
•
it does not operate properly,
•
it has been stored for a long period of time under unfavorable conditions,
•
it has been dropped or subjected to severe transport stress,
•
it has been subjected to environmental stress (corrosive atmosphere, fire, etc.).
Do not use your Reference 600 or any other apparatus if you think it could be hazardous. Have it checked
by qualified service personnel.
1-3
Chapter 1 -- Safety Considerations--Environmental Limits
Environmental Limits
Note that there are environmental limit conditions on the storage, shipping and operation of this
equipment. The Reference 600 has not been designed for outdoor use.
Storage
Ambient Temperature
Relative Humidity
-40 °C to 75 °C
Maximum 90% non-condensing
Shipping
Same as storage plus
Acceleration
Maximum 30 G
Operation
Ambient Temperature
Relative Humidity
0 °C to 45 °C
Maximum 90% non-condensing
Warning
The Reference 600 is not designed for operation in conditions where liquid water may
enter the chassis, or water vapor may condense within the chassis. Operation of a
Reference 600 that has water within the chassis can create a safety hazard, which
could result in personal injury or death.
Cleaning
Disconnect the Reference 600 from all power sources prior to cleaning.
Use a cloth lightly dampened with either clean water or water containing a mild detergent to clean the
outside of the Reference 600 enclosure. Alternatively, you can use isopropyl alcohol. Do not use a wet rag
or allow fluid to enter the Reference 600 enclosure. Do not immerse the Reference 600 in any type of
cleaning fluid (including water). Do not use any abrasive cleaners.
Service
Your Reference 600 Potentiostat/Galvanostat/ZRA has no user serviceable parts inside. You should refer all
service to a qualified service technician.
Warning
The Reference 600 must not be operated with any cover or panel on the chassis open.
Dangerous voltages may present at several points within the Reference 600 chassis,
including PC board traces. Always remove the power connection before opening the
Reference 600 case.
RFI Warning
Your Reference 600 Potentiostat/Galvanostat/ZRA generates, uses, and can radiate radio frequency energy.
The radiated levels are low enough that the Reference 600 should not create an interference problem in
most industrial laboratory environments.
The Reference 600 has been tested for both radiated and conducted RF interference and has been found
to be in compliance with FCC Part 18 and EN 61326:1998—Electrical equipment for measurement,
control, and laboratory use— EMC Requirements.
1-4
Chapter 1 -- Safety Considerations--Electrical Transient Sensitivity
Electrical Transient Sensitivity
Your Reference 600 Potentiostat/Galvanostat/ZRA was designed to offer reasonable immunity from
electrical transients, including transients on the incoming AC Mains supply and Electrostatic Discharge. It
has been tested for compliance with EN 61326:1998—Electrical equipment for measurement, control, and
laboratory use— EMC Requirements describing acceptable limits for Electrical Transient susceptibility in
Laboratory Test equipment. The Reference 600 is not rated for continuous use when subject to ESD
events. It should suffer no permanent damage when subject to the standard ESD events defined in
EN61326, but may cease normal operation until it is powered down and restarted.
In severe cases, the Reference 600 could malfunction as a result of electrical transients such as a static
discharge. If you are having problems in this regard, the following steps may help:
If the problem is static electricity (sparks are apparent when you touch the Reference 600 or it’s cables):
•
Placing your Reference 600 on a static control work surface may help. Static control work surfaces
are now generally available from computer supply houses and electronics tool suppliers. An
antistatic floor mat may also help, particularly if a carpet is involved in generating the static
electricity.
•
Air ionizers or even simple air humidifiers can reduce the voltage available in static discharges.
If the problem is AC power line transients (often from large electrical motors near the Reference 600):
•
Try plugging your Reference 600 into a different AC power branch circuit.
•
Plug your Reference into a power line surge suppressor. Inexpensive surge suppressors are now
generally available because of their use with computer equipment.
Contact Gamry Instruments, Inc. if these measures do not solve the problem.
CE Compliance
The European Community has instituted standards limiting radio frequency interference emitted by
electronic devices, setting limits for susceptibility of apparatus to RF energy and transient events, and
mandating safety requirements. Gamry Instruments, Inc. has designed and tested the Reference 600 to
comply with these standards.
The relevant CE regulations include EN 61010 and EN 61326.
RoHS Compliance
The Reference 3000 has been built using lead free components and lead free solder. It is in compliance
with the European RoHS initiative.
1-5
Chapter 2 -- Introduction--About this Manual
Chapter 2 -- Introduction
About this Manual
This manual covers the installation, safety, and use of the Gamry Instruments Reference 600
Potentiostat/Galvanostat/ZRA.
This manual describes use of a Reference 600 with Revision 5.0 (and later revisions) of the Gamry
Framework software. It is equally useful when setting up a newly purchased potentiostat or modifying the
setup of an older potentiostat for use with new software.
Chapter 1 was an in-depth discussion of safety issues. This chapter describes this manual and gives a brief
overview of the Reference 600 features. Chapter 3 is a description of the electronics circuitry in the
Reference 600. Chapter 4 contains Reference 600 installation instructions. Chapter 5 describes cell cable
connections and Chapter 6 describes the Reference 600’s Front and Rear Panels. Chapter 7 covers the
difficult issues of potentiostat stability and approaches to prevent oscillation. Chapter 8 discusses the
realities of low current, high impedance measurements.
You will find dry technical material such as specifications and connector pin-outs in the Appendices.
This manual does not discuss software installation or software operation in any detail.
Software support for the Reference 600 is described in the Gamry’s On-line Help system.
All the Gamry Instruments' applications running under the Gamry Framework, control the Reference 600
via a PSTAT object. See the Framework’s On-line Help for information concerning PSTAT objects and their
functions.
About the Reference 600
The Reference 600 Potentiostat is a research grade electrochemical instrument packaged in a small, easy to
handle case. It offers measurement capabilities similar to instruments that are more than ten times its size
and weight and more than two times its price. The Reference 600 can operate as a potentiostat, a
galvanostat, or a ZRA (zero resistance ammeter).
Reference 600 features include:
•
11 decade current auto-ranging,
•
electrical isolation from earth ground,
•
current interrupt iR compensation, and
•
both analog and digital filtering.
A sine wave generator on the Reference 600 allows its use for impedance measurements at frequencies up
to 1 MHz. Data can be acquired at frequencies up to 300000 points per second, allowing Cyclic
Voltammetry at scan rates of 1500 V/sec with 5 mV per point resolution.
A unique DSP (Digital Signal Processing) data acquisition mode allows the Reference 600 to reject noise,
from the instrument itself, from the electrochemical cell, and from the lab environment. In many cases
where other instruments require a cell in a Faraday shield to make quiet measurements, the Reference 600
can be used with the cell exposed on a bench top.
The Reference 600 offers an unprecedented combination of high speed, high sensitivity, and low noise. At
the time this is being written, the Reference 600 offers the widest EIS performance area (in a plot of
impedance versus frequency) of any Potentiostat. State-of-the-art analog components were used
throughout the design. In all design decisions, performance weighed more heavily than product cost.
2-1
Chapter 2 -- Introduction--Notational Conventions
The Reference 600, like all Gamry potentiostats, requires a computer for its use. Unlike our older
potentiostats, the Reference 600 interfaces to the computer through a USB connection. The USB
connection has become truly universal, with USB ports found on all modern computers. Gamry’s software
currently supports up to 16 Reference 600 Potentiostats connected to one computer.
The Reference 600 is isolated from earth ground. It can therefore be used to make measurements on cells
that contain an earth grounded metal. A few of the many examples of such systems are autoclaves, large
metal storage tanks, stress apparatus, and capillary electrophoresis detectors.
Notational Conventions
In order to make this manual more readable we have adopted some notational conventions. These are
used throughout this manual and all other Gamry Instruments manuals:
•
Numbered lists. A numbered list is reserved for step-by-step procedures, with the steps always
performed sequentially.
•
Bulleted list. The items in a bulleted list, such as this one, are grouped together because they
represent similar items. The order of items in the list is not critical.
•
File names and folders. Inside paragraphs, references to computer files and Windows folders will
be capitalized and placed within quotes, for example: “C:\MYGAMRYDATA\CV.DTA" and
“GAMRY5.INI".
2-2
Chapter 3 -- Instrument Circuitry--Reference 600 Schematic/Block Diagrams
Chapter 3 -- Instrument Circuitry
Reference 600 Schematic/Block Diagrams
If you are not familiar with electronic schematics or potentiostats, you probably want to skip this chapter.
This information is for expert use only and is not required for routine use of the Reference 600.
The following figures are partly schematic diagrams and partly block diagrams. They are intended to show
the basic principles of the Reference 600 without the confusion of the full circuitry details. The complexity
of the Reference 600 can be quite daunting – the Reference 600 circuit boards contain more than 2500
components connected by almost 2000 circuit nets!
The schematic/block diagram figures show:
•
the potentiostat board in its potentiostatic control mode,
•
the control board circuits for signal generation,
•
the control board circuits for signal conditioning and A/D conversion,
•
the Auxiliary ADC channel input switching,
•
the processors in the Reference 600,
•
DC-DC power conversion.
3-1
Chapter 3 -- Instrument Circuitry--Reference 600 Schematic/Block Diagrams
Figure 3-1
Reference 600 Potentiostat Board in Potentiostat Mode
Simplified Schematic/Block Diagram
Notes for Figure 3-1
•
Only Potentiostat Mode circuitry is shown in this figure. In this mode the voltage difference
between the Reference and Working Sense leads (called Esig) is feedback into the control amplifier.
In Galvanostat Mode, the feedback is from Isig.
3-2
Chapter 3 -- Instrument Circuitry--Reference 600 Schematic/Block Diagrams
In ZRA mode, the feedback is from a differential amplifier measuring the difference between the
Counter Sense and Working Sense leads of the cell cable. The counter sense circuitry is not shown.
It is conceptually similar to the voltage sensing circuit that generates Esig.
•
The Bias DAC and PFIR (Positive Feedback IR compensation) DAC are set using a computer bus
that is not shown.
•
Switches are either reed relays or MOS switches as appropriate. All switches are under computer
control (obviously, since the Reference 600 does not have a knob and dial front panel).
•
All components shown as being variable (resistance Rm, capacitor IEStab and capacitor CASpeed)
are actually several fixed value components switched into the circuit. They are not continuously
variable as implied in the figure.
•
The monitor BNC connectors for Isig and Esig are lightly filtered using an RLC circuit.
•
The programmable attenuator on Esig prior to the ADC channel scales Esig so that it is compatible
with the A/D channel’s ± 3 volt input range. The 0.25 gain setting allows the Reference 600 to
measure potential signals slightly in excess of 10 volts (on a 12 volt full scale range). Isig is gained
to be 3 volts full-scale so it does not require a similar attenuation function.
•
All the resistors summing voltages into the Control Amplifier input do not have values shown – their
values depend on scaling factors too complex to discuss in this simplified diagram.
•
Calibration components are not shown.
•
Gamry’s software can disconnect the signal generator from the Potentiostat. Once disconnected it
can be used for other experimental control tasks.
•
Overload protection and overload detection are not shown. Good engineering practice demands
that any possible misconnection of the cell leads will not damage the instrument. This practice has
been followed in the Reference 600 design.
3-3
Chapter 3 -- Instrument Circuitry--Reference 600 Schematic/Block Diagrams
Figure 3-2
Reference 600 Signal Generation Circuitry
Notes on Figure 3-2:
•
All the resistors summing voltages into the Summing Amplifier input do not have values shown
because their values depend on scaling factors too complex for this simplified diagram.
•
The IR DAC has a ± 8 volt full-scale range.
•
Calibration components are not shown.
•
The DDS can generate fixed amplitude sine waves with frequencies between 1 MHz and 1 mHz.
In practice, Gamry’s EIS300 software uses the Scan DAC to generate sine signals if frequency is
below 1 Hz.
The low pass filter removes high frequency distortion in the “raw” DDS output.
The attenuator scales the DDS. The maximum output signal is 4.096 volts peak-to-peak and the
minimum is approximately 20 µV peak-to-peak.
•
The BNC connector for Sig Gen out is lightly filtered using an RLC circuit.
3-4
Chapter 3 -- Instrument Circuitry--Reference 600 Schematic/Block Diagrams
Figure 3-3
One A/D Signal Chain in the Reference 600
Notes for Figure 3-3:
•
This diagram shows one of three identical ADC channels. One channel is dedicated to
measurement of the potentiostat’s current signal, another is used to measure the voltage, and the
third is switched between a wide selection of possible signals.
•
All three A/D converters are triggered simultaneously to start a conversion. This trigger and the
pulse updating the Scan DAC voltage are under the control of a hardware state-machine. This
insures that all waveform and data acquisition timing is tightly controlled and reproducible point-topoint.
By default, the data acquisition is synchronized with the 300 kHz power supply switching
frequency, to reduce noise due to the power supply. Data acquisition times that are a multiple of
3.333 µSec will maintain this synchronization.
•
All analog signals that cross from the Potentiostat Board to the Control Board or vise versa are
received differentially as shown here.
•
The 5 Hz, 1 kHz, and 200 kHz filters are 2-pole Butterworth filters. The 3 MHz RLC filter has an
arbitrarily selected transfer function.
•
All signal channel components are selected for optimal DC accuracy, low noise, and high
bandwidth.
3-5
Chapter 3 -- Instrument Circuitry--Reference 600 Schematic/Block Diagrams
Figure 3-4
Aux Channel Input Switching
Notes for Figure 3-4:
•
Two ADC Channels are dedicated to the potentiostat’s voltage and current signals. This diagram
shows the signals that can be connected to the third channel.
•
The Aux ADC BNC input is a differential input. It is shipped configured for input impedance of
100 kΩ and unfiltered operation. Jumpers on the controller board allow it to be configured for high
input impedance and to allow input filtering.
•
The thermocouple input allows for connection of a J Type or K Type thermocouple, depending
upon the date of manufacture. The type of thermocouple is shown next to the connector on the
rear of the instrument. Note that this circuit must be calibrated to obtain reasonable accuracy. A
section of the Reference 600 calibration procedure allows for user calibration of this input.
•
The other two inputs to the Aux channel are reserved use in future Gamry Instruments’ systems.
3-6
Chapter 3 -- Instrument Circuitry--Reference 600 Schematic/Block Diagrams
Figure 3-5
Microprocessors in the Reference 600
Notes for Figure 3-5:
•
Note the lack of a ground connection between the USB bus and the Reference 600 circuitry.
•
The EasyUSB firmware is loaded into EasyUSB RAM on power-up. The USB firmware can be
updated over the USB via a selection in the Reference 600 section in the Windows Device
Manager.
•
The Power PC firmware is also transferred from ROM into RAM on power-up. The Power PC
firmware can also be updated over the USB via a selection in the Reference 600 section of the
Windows Device Manager. Time critical sections of the Power PC code are kept in the processor’s
fast cache memory.
•
The term UART refers to a Universal Asynchronous Receiver Transmitter. It converts parallel data to
a self-clocking serial bit stream. The UARTs send data at 6 Mbits/second.
•
The Bus Transceiver isolates bus activity on the Controller and Potentiostat boards. Only reads and
write to locations on these boards generate bus activity. This reduces noise pick-up.
•
Each board in a Reference 600 has local non-volatile data storage. This is used to save calibration
data and board revision information. Unlike previous Gamry Instruments Potentiostats, the
Reference 600 calibration data stored in the instrument, not in a data file. When a Reference 600
is moved from one computer to another, its calibration remains valid.
3-7
Chapter 3 -- Instrument Circuitry--Reference 600 Schematic/Block Diagrams
Figure 3-6
DC-DC Power Conversion
Notes for Figure 3-6:
•
Note the ground isolation between the input power and the Reference 600 circuitry. The
Reference 600 chassis is connected to the Floating Instrument Ground.
Transformers and opto-isolaters are the only components connected between the grounds.
•
The 300 kHz power supply sync signal is derived from the same clock used to control data
acquisition. Data points taken at an integer multiple of 3.333 µSec/point will be synchronized with
the power supply, minimizing the effect of power supply noise on the data.
•
Additional circuitry that is not shown protects the Reference 600 against ESD (electrostatic
discharge) and electrical surges. Not that the Reference 600 is also protected against damage if an
incorrect polarity power input is connected to the unit.
•
The incoming DC voltage must be between 22 and 26 volts. With inputs below 22 volts, the
PWM (Pulse Width Modulator) may be unable to regulate the supply. Above 26 volts, the PWM
may not start-up.
Warning
Do not use a DC power source other than the AC adapter model provided with your
Reference 600. Other replacements may void the performance and/or safety
characteristics of the Reference 600.
Caution
Power input voltages less than 20 volts or greater than 32 volts can damage the
Reference 600’s power supply.
3-8
Chapter 4 -- Installation--Reference 600 Schematic/Block Diagrams
Chapter 4 -- Installation
This chapter of the Gamry Instruments Inc. Reference 600 Operator's Manual covers normal installation of the
Reference 600. We assume the Reference 600 is installed as part of a Gamry Framework based
electrochemical measurement system containing a Microsoft Windows compatible computer.
Figure 4 - 1
Front View of a Reference 600
4-1
Chapter 4 -- Installation--Initial Visual Inspection
Initial Visual Inspection
After you remove your Reference 600 from its shipping carton, you should check it for any signs of shipping
damage. If any damage is noted, please notify Gamry Instruments, Inc. and the shipping carrier immediately.
Save the shipping container for possible inspection by the carrier.
Warning
The “reinforced insulation” that keeps the operator from accessing the “hazardous live” voltages
in the Reference 600 can be rendered ineffective if the Reference 600 is damaged in shipment.
Do not operate damaged apparatus until a qualified service technician has verified its safety.
Tag a damaged Reference 600 to indicate that it could be a safety hazard.
Warning
If the Reference 600 is taken from a cold location (for example outdoors in winter conditions) to
a warm humid location, water vapor could condense on the cold surfaces inside the Reference
600, possibly creating a hazardous condition. The “reinforced insulation” that keeps the
operator from accessing the “hazardous live” voltages in the Reference 600 can be rendered
ineffective if the Reference 600 has condensed water inside its case. Before connecting power to
a “cold” Reference 600, allow at least one hour for the Reference 600 to warm at room
temperature.
Physical Location
You normally locate your Reference 600 on a flat workbench surface. You will want to have access to the rear
of the instrument because some cable connections are made from the rear. The Reference 600 is generally
operated in an up-right position (see Figure 4-1). Operation in other positions is possible as long as you insure
that air movement through the chassis is not restricted.
Caution
Do not block the airflow into or out of the Reference 600 chassis. While the circuitry should
suffer no damage due to excessive heat, the Reference 600 enclosure may become
uncomfortably hot to the touch if no air flows through the chassis. Running the Reference 600
without adequate cooling could shorten the time to failure of some of the circuitry.
If you do place your Reference 600 within an enclosed space, make sure that the internal temperature within
that space does not exceed the 45°C ambient temperature limit of the Reference 600. Be particularly careful
if a computer or other heat dissipating equipment is mounted in the same enclosure as the Reference 600.
The Reference 600 has not been designed for outdoor use.
Computer Requirements
Before you connect a Reference 600 to a computer you must make sure that your computer meets these
simple requirements.
•
A computer based on one of the Pentium family of Intel microprocessors or a 100% compatible
processor from another vendor.
•
One of the following Operating Systems: Microsoft® Windows XP Service Pack 2, Windows
Vista®, or 7 is required. (See Gamry’s website “www.gamry.com” if you have a newer edition of
Windows).
•
A USB port that supports Full Speed (12 Mbits/second) or High Speed (480 Mbits/second) USB
transfers. It must be compatible with Revision 1.1 or Revision 2.0 of the USB specification.
4-2
Chapter 4 -- Installation--Plug & Play System Configuration
Plug & Play System Configuration
The Reference 600 is completely compatible with the Windows Plug & Play configuration system. Like most
Plug & Play hardware, it is best if you install the software for the Reference 600 before you install the
potentiostat hardware.
A Setup program will normally startup automatically when you place the Gamry Instrument’s Software CD into
the CD drive on your computer. Consult Gamry’s software installation manual if you need assistance
accessing the Setup program or choosing options in its menus.
4-3
Chapter 4 -- Installation--Power Cord and Power Connection
Figure 4 - 2
(Preliminary) Rear Panel of the Reference 600
Power Cord and Power Connection
The Reference 600 does not plug directly in the AC mains supply. Instead, the mains are connected to an
external power supply, which supplies a regulated 24-volt DC output. This regulated DC is then connected to
the DC power input jack on the rear of the Reference 600.
4-4
Chapter 4 -- Installation--Power Up Test
The external power supply provided with the Reference 600 is rated for operation from 100 to 240 Vac, at
frequencies from 47 to 63 Hz. It should therefore be useable worldwide.
The Reference 600 external supply is supplied with a line cord suitable for use in the United States. In other
countries, you may have to replace the line cord with one suitable for your electrical outlet type. You must
always use a line cord with a CEE 22 Standard V female connector on the apparatus end of the cable. This is
the same connector used on the US standard line cord supplied with your Reference 600. See Chapter 1 for
specific safety information regarding line cord selection.
The DC output cord from the external power supply plugs into the DC Power input jack on the rear panel of
the Reference 600 (see Figure 4 - 2).
Power Up Test
Before you make any other connections to your Reference 600 you should check that the Reference 600 is at
least nominally functional.
One quick test is to power up the Reference 600 and watch the blue power LED indicator on the front panel
of the Reference 600 (see Figure 4 - 1).
After connecting DC power to the Reference 600, turn on the Power switch on the rear panel of the Reference
600 (see Figure 4 - 2).
Watch the Power LED as the Reference 600 powers up. This LED should go on for a second or so, flash three
times, then remain on.
The status of the other LED indicators is not important at this time.
Each flash of the power LED flashes corresponds to successful conclusion of one portion of the Power PC’s
power-up self-test.
If the power LED goes on, then turns off and stays off, the Reference 600 is not working properly! Contact
Gamry Instruments or your local Gamry Instruments representative as soon as possible if this power up test
fails.
USB Cabling
The Reference 600 connects to the computer using a standard High Speed USB A/B cable. A suitable cable
was shipped with your Reference 3000. If this cable has been lost, you can get a replacement at almost any
computer retailer. The replacement cable should be rated for USB 2.0 high speed USB operation.
An A/B USB cable has different connectors on each end. The end with a wider, rectangular shaped connector
plugs into a USB port on your computer (or a similar port on a USB hub). The end with a nearly square
connector plugs into the USB port on the Reference 600 (see Figure 4 - 2).
The USB connection can be “hot-plugged”. This means, both the computer and the Reference 600 can be
powered-up before the USB cable is plugged in. Unlike many other instrument system connections, you need
not power down the system before plugging in the USB.
You can also safely remove the USB cable without powering down the Reference 600 and your computer. Be
aware however, that this may have undesirable consequences if the system is currently taking data or
performing an electrochemical experiment.
4-5
Chapter 4 -- Installation--Front Panel USB LED
Front Panel USB LED
The front panel USB LED provides a simple test of two aspects of normal Reference 600 USB operation. It has
three normal states:
•
Unlighted, indicating that the USB cable is disconnected or the USB connection is disabled by the
host computer,
•
Solid Green, indicating that a valid cable connection has been made and the Reference 600 USB
processor is receiving power from the USB cable,
•
Flashing Yellow, indicating that valid USB messages are being transferred between the computer
and the Reference 600.
The flashing state will only be seen when Gamry Instruments application software is running.
1st Time Device Installation in Windows
When a Reference 600 is first connected to a computer running Windows, the Windows Plug and Play
Manager will see the new device, but will be uncertain what device it is. The message that will appear is
something like “New device found” or “Unknown USB device Detected”.
When this occurs after you’ve connected a Reference 600, tell Windows that you would like to install the new
device.
Windows 7 Users: The following windows will not be displayed. Please skip to page 4-8 to continue the
installation process.
All other users should see a screen that looks something like this:
Figure 4 - 3
Welcome to the Found New Hardware Wizard
4-6
Chapter 4 -- Installation--1st Time Device Installation in Windows
As shown in this Figure, do not choose to let Windows Update find the device driver that you need. The
Windows Update web site has no knowledge of the Gamry Instruments Reference 600.
Make sure you select No, not this time. After you select, Next, you should see a screen that looks like this:
Figure 4-4
Install the Software Automatically
All Gamry device drivers are pre-installed to your machine during the software installation process. Select
Install the software automatically, then select Next.
These messages will also be seen when a Reference 600 instrument is moved to a new USB port. In this case,
you can still select Install the software automatically, even if you do not have the Gamry Instruments CD.
The driver that was previously installed on your computer’s disk drive will be used.
The Windows Device Manger will locate and install the required files, which are already on your system.
Your Gamry Software CD is not required at this point. However, if you do not have your Gamry Software CD
or lose the CD at any point, contact Gamry Instruments, or your local Gamry Sales representative for
assistance.
Once the drivers and associated support files have been installed, you should see another screen that looks like
this:
4-7
Chapter 4 -- Installation--1st Time Device Installation in Windows
Figure 4-5
Enter New Device Information
As displayed in Figure 4-5, you enter a friendly name for your Reference 600, as well as any authorization
codes you received with your instrumentation. The authorization codes are 10 digit codes that allow different
Gamry application software to be used with your Reference 600. If you cannot locate your authorization
codes, please contact Gamry Instruments or your local Gamry Sales representative for assistance.
To enter an authorization code, simply click on the Add button. A dialog box will appear as shown in Figure
4-6. You enter the package name, like “EIS300”, followed by the 10 digit authorization code.
Figure 4-6
Enter an Authorization Code
Press OK when you are finished.
On occasion you may desire to change the USB port which is used to connect the Reference 600 to your
computer. The same procedure discussed above may need to be followed for each USB port on your
computer, depending upon your operating system requirements. Once the Reference 600 has been
4-8
Chapter 4 -- Installation--Multiple Potentiostat Systems
connected to a port, removing and reconnecting to that port will no longer require any device installation. If
you expect to switch between multiple USB ports on your computer, it is recommended to go through each of
the ports in sequence while your installation CD is handy. Once you have done this, store the installation CD
in a safe place.
Multiple Potentiostat Systems
Gamry’s current Framework software (Revision 5.0) allows a computer to operate up to 16 Gamry Instruments
potentiostats simultaneously. The 16 potentiostats can include both Reference 600s and older PCI4 family
devices.
A system with multiple Reference 600s just needs them all plugged into the computer. We do not
recommend using bus-powered hubs to expand your USB network. Externally powered USB hubs are
commonly available.
Contact our home office or your local Gamry Instruments representative if you need assistance configuring a
system containing both Reference 600 and PCI4 hardware.
Cell Cable Installation
The Cell Connector is a 25-pin female D connector on the front of the Reference 600 (see Figure 4 - 1).
All Gamry’s standard cell cables have a 25-pin D connector on one end and a number of leads terminated
with banana plugs on the other. The D connector end of the cable is connected to the Cell Connector on the
front of the Reference 600. The knurled screws on this cable should always be used to hold the cable in place.
A wide variety of cell cables are available for the Reference 600. These include unshielded cables designed for
maximum AC performance, shielded cables in various lengths, and special cables for use in EIS systems where
very low impedances must be measured. The Reference 600 can automatically detect which Gamry
Instruments cable is connected and the Gamry Framework software can then adjust the system performance
for the characteristics of that cable.
Device Manager
If you wish to make changes to the configuration of your Reference 600 after it has already been installed, you
must use the Windows Device Manager. Steps for getting to the Device Manager can vary by operating
system, so check your operating system’s online help for more specific information on how to get to the
Windows Device Manager.
Under Windows XP, right clicking on the My Computer icon and selecting Properties brings up the System
Properties dialog box. Select the Hardware Tab and then click on the Device Manager button. This should
bring up the Device Manager screen. Clicking on the + sign next to Gamry Instruments, should expand the
tree view to give you a screen that looks similar to the following figure:
4-9
Chapter 4 -- Installation--Authorization Codes and Label
Figure 4-7
Device Manager Window
You can now right click on any of the Devices listed under Gamry Instruments and select Properties to look at
or change its configuration.
Authorization Codes and Label
If you purchase additional Gamry application software, did not enter your authorization codes upon initial
device installation, or simply need to make a correction to your authorization codes, you can do so using the
Windows Device Manager. You can also change the Label you use for your device. The Gamry Framework
Application Software must first be closed before you can use the Device Manager to make changes. Next, you
must select the appropriate device, as discussed in the Device Manager section. Once you have selected the
appropriate device, right click and select Properties. Next, select Device Settings and you will see a screen
that looks like Figure 4-8:
4 - 10
Chapter 4 -- Installation--Firmware Update
Figure 4-8
Device Settings Tab
You can enter or edit any of the authorization codes or Label for the device by clicking on the appropriate edit
box and entering the information. When you are finished making changes press OK to store the changes.
Firmware Update
Your Reference 600 was shipped with the latest version of Firmware. From time to time, however, Gamry
makes changes to the instrument code, and a firmware update will be required to make use of the new or
improved code.
There are two separate code images that can be field updated on your Reference 600. The first is the
Instrument Code. This is the code that handles most of the functionality of the Reference 600. The second is
the Communications Code. This code handles the USB communications between your Reference 600 and
the host computer.
Appropriate update files (code images) can be obtained from the Gamry Instruments website at
www.gamry.com. Download the file containing the new code and save it onto your computer’s hard disk.
Alternatively, Gamry’s software CD contains a firmware folder that contains firmware files compatible with that
CD’s Framework revision.
4 - 11
Chapter 4 -- Installation--Firmware Update
You must first close the Gamry Framework Software before proceeding to update any code in the device. To
update either of these code images, you must first select the appropriate device in the Device Manager, as
discussed in the Device Manager section. Once you have selected the appropriate device, right click and
select Properties. Next, select Firmware and you will see a screen that looks like Figure 4-9:
Figure 4-9
Firmware Update Tab
Depending upon which code you wish to update, click on either Update Instrument Firmware, or Update
Communications Firmware. You will then be prompted for a file. Navigate to the location firmware file’s
location (on the Gamry software CD or on your computer’s hard drive) and then press Open. The update
procedure will begin. You should see a status bar that shows the progress of the update. The USB indicator
on the Reference 600 should also turn red during the procedure. Once the update is successful, press OK.
Your Reference 600 in once again ready for use.
Appropriate updates can be obtained from the Gamry Instruments website at www.gamry.com. Should you
encounter a problem updating the firmware in your Reference 600, please contact Gamry Instruments for
assistance.
4 - 12
Chapter 4 -- Installation--Application Software Installation and System Checkout
Interrupting a firmware download can cause a catastrophic failure of your system. Do not turn off the
Reference 600, do not unplug the USB cable, and do not stop the host computer operation when the USB
LED is a steady red color.
Caution
Do not interrupt a firmware download that is in progress. An incomplete download can render a
Reference 600 inoperable until it is returned to Gamry for reprogramming.
Application Software Installation and System Checkout
Software installation is slightly different for each Gamry Instruments, Inc. application package. Refer to the
software installation instructions in the Installation Manual for each application package in your system.
You should also perform the system checkout procedures for each application. Follow the instructions in each
application's Installation Manual. The system checkout procedures check for correct hardware and software
installation. They are not a comprehensive test of each facet of system operation.
Calibration
After you have run the system checkout procedure(s), you should calibrate each potentiostat installed in your
system. A calibration script is provided with the Gamry Framework. The Installation Manual for every major
application package contains instructions for calibration using this script.
The calibration for the Reference 600 has been divided into three sections: DC Calibration, AC Calibration,
and Low I DC Cal. All three calibration procedures are accessed via a new Utility selection on the
Framework’s Experiment pull down menu.
Separate Calibration for Each Reference 600 Cable Type
The Reference 600 now recognizes the type of cable connected to its cell connector. It maintains a separate
AC calibration table for each type of cable. The Gamry Framework will not let you use AC calibration data
recorded using a 60 cm shielded cable for experiments run using a Twisted Pair cable optimized for low
impedance EIS measurements.
DC and AC Calibration
These two procedures use an external resistive dummy cell.
CAUTION:
Reference 600 calibration calls for an external resistive dummy cell. Your Reference 600 was
shipped with a Universal Dummy Cell 4, which includes a 2 kΩ
Ω, 0.05% accurate resistor in the
position marked “Calibration”. After calibration, please place this dummy cell in a safe place
where you can find it if your unit requires recalibration.
If you do need to recalibrate and you cannot find your Universal Dummy Cell 4, you can perform
DC Calibration using a different 2 kΩ
Ω resistor. Its wattage is unimportant. Some performance
checks in the calibration process may fail if the resistors inaccuracy exceeds 0.2% (4 Ω).
We do not recommend AC Calibration with any resistor other than the one on the Universal
Dummy Cell 4. The Universal Dummy Cell 4 was designed to separate the working electrode
leads from the counter and reference electrode leads. If you perform AC Calibration without
adequate separation between these leads, you will see phase shift in your high frequency EIS
data. 1.4 pF of stray capacitance across a 200 Ohm resistor causes a 1°° phase shift at 1 MHz.
4 - 13
Chapter 4 -- Installation--Calibration
Potentiostat calibration is only required infrequently. You should recalibrate your Reference 600 under the
following circumstances:
•
It has been about one year since your last calibration.
•
Your potentiostat has been serviced.
•
You notice breaks or discontinuities in the data curves recorded with your system.
•
You are running the system in a very different environment you used when the unit was last
calibrated. For example, if the Reference 600 was calibrated at 15 °C and you are now operating
it in at 30 °C, you should recalibrate.
Figure 4-10
UDC4 With Leads Attached for Calibration
Low I Range DC Calibration
The standard Reference 600 calibration is performed with the cell leads connected to a 2 kΩ resistor. During
the calibration procedure, DC current range offsets are recorded with the cell switch turned off. A DC current
measurement is made on each of the 11 current ranges in the Reference 600. The measured current on each
range is the sum of current contributions from:
•
The input current of the I/E Converter input amplifier,
•
the input current of the Working sense input amplifier,
•
the input current of the Reference input amplifier,
4 - 14
Chapter 4 -- Installation--Calibration
•
the input current of a Counter Sense input amplifier,
•
current leakage in the cell switch.
In most real-world experiments, the cell is turned on, and the I/E converter does not measure the last three
terms listed above. These currents still exist, but they are generally sourced by the low impedance counter
electrode lead. Only the first two terms still in the cell current as measured by the I/E Converter.
The current contributions from each source on the above list are (at most) a few pA, so they are insignificant
on all but the most sensitive Reference 600 current ranges – the 60 pA and 600 pA ranges.
This effect can cause differences of up to 8 pA between DC current measured with the cell turned off and
current measured with the cell turned on. In most cases the difference is smaller – one or two pA.
Only two Reference 600 applications are sensitive enough that this current measurement offset causes
problems. One is Physical Electrochemistry (Cyclic Voltammetry for example) with small electrodes and the
second is EIS on high impedance samples such as barrier coatings. Incorrect DC current readings in EIS can
slow the experiment, since the automatic ranging algorithms in the EIS300 software can make poor range
choices given incorrect data. This can significantly lengthen the time needed to measure an EIS spectrum.
Most corrosion experiments or macro-electrode measurements involve currents much too large to be affected
by this difference.
The Gamry Framework now includes a special “Low I DC Current” calibration procedure that corrects the
Reference 600 offsets to minimize this problem. The procedure uses a script that:
1)
asks you to disconnect the reference, counter, and counter sense leads from the calibration cell,
2)
measures the I/E input and Working sense amp input currents on the 60 pA and 600 pA ranges,
3)
replaces the 60 pA and 600 pA current range offsets measured in the full DC calibration with these
improved values.
The error sources listed above are both time and temperature dependent, so we recommend frequent “Low I
DC Calibration” - if you need accurate measurement of absolute currents at pA levels. The procedure runs
fairly quickly, so daily or weekly calibration should not be too inconvenient.
NOTE:
The Low I DC Calibration is not a full calibration. You must run a full DC Calibration on your
Reference 600 before you first run the “Low I DC calibration”. Remember that the Reference
600 must have a full DC calibration on the same type of cable you are using for the Low I DC
Calibration.
4 - 15
Chapter 5 -- Cell Connections--Normal Cell Connections
Chapter 5 -- Cell Connections
Normal Cell Connections
Each Reference 600 in your system was shipped with a standard, shielded cell cable. The Gamry part number
for this cable is 985-00071. It is a 60 cm complex cable with a 25-pin D type connector on one end and four
banana plugs and two pin jacks on the other end.
In some cases, your system may also include a special purpose cell cable. The special purpose cell cable will
include documentation describing its use.
The 25-pin male end of the standard cell cable connects to the Reference 600’s front panel Cell Connector.
You should always screw the cell cable into place since this cable can fall off the unit. This can be disastrous if
it occurs during an experiment.
The other end of the cell cable terminates in a number of banana plugs and two pin jacks. Each termination
comes with a removable alligator clip. Table 5-1 identifies each terminal of the cable.
Table 5-1
Cell Cable Terminations - Potentiostat and Galvanostat Modes
Color
Type
Name
Normal Connection
Blue
Banana Plug
Working Sense
Connect to working electrode
Green
Banana Plug
Working Electrode
Connect to working electrode
White
Pin Jack
Reference
Connect to reference electrode
Red
Banana Plug
Counter Electrode
Connect to counter electrode
Orange
Banana Plug
Counter Sense
Used in ZRA mode - connect to counter electrode
Black
Pin Jack
Floating Ground
Leave open or connect to a Faraday shield
Connect both the blue and green cell leads to the working electrode. The working electrode is the specimen
being tested. The blue pin jack connection senses the voltage of the working electrode. The green working
electrode connection carries the cell current. The working electrode may be as much as 150 mV above the
circuitry ground (floating ground).
Connect the white pin jack to the cell's reference electrode, such as an SCE or Ag/AgCl reference electrode.
The measured cell potential is the potential difference between the blue and white cell connectors.
Connect the red banana plug to the counter or auxiliary electrode. The counter electrode is usually a large
inert metal or graphite electrode. The counter electrode terminal is the output of the Reference 600's power
amplifier.
The orange lead is only used in ZRA mode where it senses the counter electrode potential (see following
section). Automatic switching to ZRA mode is possible if this lead is connected to the counter electrode. If you
will not be using ZRA mode, this lead can be left open as long as you insure that it will not short against any
other electrode.
The black pin jack is connected on the Reference 600 end to Floating Ground. This is the circuitry ground for
the analog circuits in the Reference 600. In most cases, this terminal should be left disconnected at the cell
end. When you do so, take care that its metal contact does not touch any of the other cell connections.
5-1
Chapter 5 -- Cell Connections--ZRA Mode Cell Connections
If your cell is a typical glass laboratory cell, all of the electrodes are isolated from earth ground. In this case, you
may be able to lower noise in your data by connecting the Reference 600’s Floating Ground to an earth
ground.
A binding post on the rear panel of the Reference 600 is provided for this purpose. A water pipe can be
suitable sources of earth ground.
Caution
If any electrode in your cell is at earth ground, you must not connect the Reference 600
chassis to earth ground. Autoclaves, stress apparatus, and field measurements may
involve earth grounded electrodes.
Warning
Make sure that your earth ground connection is made to a legitimate source of earth
ground. Consult a qualified electrician if you are uncertain how to obtain an earth
ground. Connecting the Reference 600 to an incorrect and unsafe voltage can create a
safety hazard (see Chapter 1 for details).
If you are measuring very small currents, you may find that a metal enclosure completely surrounding your cell
(a Faraday shield) significantly lowers measured current noise. This Faraday shield should usually be connected
to both earth ground and Floating Ground. The Floating ground on the black cell lead is a convenient source
of ground.
If any electrode in your cell is connected to earth ground, you should only connect your Faraday shield to the
black cell lead (Floating Ground).
The alligator clip on any cell connection can be removed to access the underlying banana plug or pin jack. If
you need to permanently change the terminations on your cell cable, feel free to remove the banana plugs and
replace them with your new termination. Gamry Instruments can also provide additional standard or special
cell cables.
In either potentiostatic or galvanostatic mode, if you do not have a reference electrode in your cell, the
reference lead can be connected to the counter electrode for a two electrode experiment. The potential reading
will be the difference between the counter electrode and the working electrode.
ZRA Mode Cell Connections
The Reference 600 can function as a precision Zero Resistance Ammeter (ZRA). It maintains two metal samples
at the same potential and measures the current flow between the samples. It can also measure the potential of
the samples versus a reference electrode.
The cell cable connections for ZRA mode are shown in Table 5-2. Note that the connections are very similar to
those for the potentiostat and galvanostat modes. A second working electrode is substituted for the counter
electrode and the Orange Counter Sense lead must be connected.
5-2
Chapter 5 -- Cell Connections--Membrane Cell Connections
Table 5-2
Cell Cable Connections for ZRA Mode
Color
Type
Name
Normal Connection
Blue
Banana Plug
Working Sense
Connect to metal sample #1
Green
Banana Plug
Working Electrode
Connect to metal sample #1
White
Pin Jack
Reference
Connect to a reference electrode
Red
Banana Plug
Counter Electrode
Connect to metal sample #2
Orange
Banana Plug
Counter Sense
Connect to metal sample #2
Black
Pin Jack
Floating Ground
Leave open or connect to a Faraday shield
The counter sense and the working sense lead are each connected to different metal samples. In the ZRA
mode the Reference 600 is normally programmed to maintain zero volts between these leads. It therefore
maintains the two metal samples at the same voltage.
The white pin jack on the cell cable is normally connected to a reference electrode. The potential between
this lead and the working sense lead is reported as the cell potential.
In ZRA mode, if you don’t have a reference electrode in your cell, we recommend that you connect the white
reference lead to the working electrode. In theory, the measured potential will be exactly zero when this is
done. In practice, A/D noise and offset will create a small potential signal with a value very close to zero.
Membrane Cell Connections
The Reference 600 can be used with membrane cells. In this type of cell, a membrane separates two
electrolyte solutions. Two reference electrodes are used - one in each electrolyte. Each electrolyte also
contains a counter electrode. The Reference 600 controls the potential across the membrane. Table 5-3 shows
the cell connections used with a membrane type cell.
Table 5-3
Cell Cable Connections for a Membrane Cell
Color
Type
Name
Normal Connection
Blue
Banana Plug
Working Sense
Connect to reference electrode #1
Green
Banana Plug
Working Electrode
Connect to counter electrode #1
White
Pin Jack
Reference
Connect to reference electrode #2
Red
Banana Plug
Counter Electrode
Connect to counter electrode #2
Orange
Banana Plug
Counter Sense
Leave open (only needed in ZRA mode)
Black
Pin Jack
Floating Ground
Leave open or connect to a Faraday shield
Note that reference electrode #1 and counter electrode #1 must be on one side of the membrane and
reference electrode #2 and counter electrode #2 must be on the other side.
5-3
Chapter 6 -- Panel Indicators and Connectors--Front Panel
Chapter 6 -- Panel Indicators and Connectors
Front Panel
The Reference 600 front panel includes one connector and 4 backlighted LED indicators. Each of these will be
discussed in turn. A picture of the Reference 600 front panel can be seen in Figure 4 - 1.
Cell Connector
The Cell Connector is a 25-pin D type connector that is used to connect the Reference 600 to an
electrochemical test cell. It is normally used with a Gamry Instruments supplied cell cable.
In addition to the pins used for cell connections, the Reference 600 Cell Connector also uses 5 pins to read a
cell cable ID. Gamry’s software can compensate for the cell cable characteristics for optimal system
performance, especially in EIS (Electrochemical Impedance Spectroscopy).
The cell connections are discussed at great length in Chapter 5. A pin-out of the cell cable connector can be
found in Appendix B.
The Power LED
The Power LED is located on the lower left of the Reference 600 front panel. It normally glows a steady blue,
when the Reference 600 is turned on and has passed some simple self-tests.
When the Reference 600 is first turned on, the Power LED will glow steadily for a second or two, blink three
times, and then go to its normal steady blue output. Each blink in this sequence indicates successful
completion of a portion of the Power PC’s power-up self-test routine.
When the Power LED is off, either:
•
The rear panel power switch is off.
•
There is no DC +24 volt supply connected to the rear panel DC Power In connector.
•
The external DC power supply has no input power or is malfunctioning.
•
One part of the Power PC’s power-up self-test has failed.
Caution
The Power LED is used both to indicate power status and to indicate that power-up tests
have passed. It therefore cannot be relied on as a true power status indicator. Always
unplug the DC Power In connection if you suspect your Reference 600 is malfunctioning.
The USB LED
The USB LED is located just above the Power LED. It is a tri-color LED, capable of glowing green, orange, or
red.
The USB LED will be unlighted when:
•
The Reference 600 is not powered.
•
The Reference 600 does not have a USB cable plugged into its rear panel USB port.
•
The computer end of the USB cable is not plugged into a USB port on a computer or hub.
•
The USB cable is not supplying USB power to the Reference 600.
•
The computer has disabled the USB port going to the Reference 600.
6-1
Chapter 6 -- Panel Indicators and Connectors--Front Panel
The USB LED will glow a steady green if a valid USB connection has been made and the Reference 600’s
communication processor is receiving power down the USB cable.
The USB LED will flash orange whenever the Reference 600 is receiving or transmitting valid USB messages to
or from the host computer. It will not flash if there is USB traffic addressed to other devices on the USB bus,
including messages aimed at a different Reference 600.
The USB LED will indicate a sold RED in one special condition. It will be red when a firmware download is
taking place. Interrupting a firmware download can cause a catastrophic failure of your system. Do not turn off
the Reference 600, do not unplug the USB cable, and do not stop the host computer operation when the USB
LED is a steady red color.
Caution
Do not interrupt a firmware download while it is in progress. An incomplete download
can render a Reference 600 inoperable until it is returned to Gamry for reprogramming.
Cell LED
The Cell LED glows yellow whenever the Reference 600 is actively applying voltage or current to the
electrochemical cell attached to the Cell Cable. You should avoid touching the cell cable leads whenever the
Cell LED is lighted, because the quality of the data being collected in your experiment may be compromised.
Note
The Cell LED does not indicate a dangerous condition when it is lighted. The voltages
output by the Reference 600 are generally considered to be safe. Still, you should avoid
touching the cell leads when the cell is on.
If you need to make changes to your cell leads, you normally do so between experiments, when the Cell LED is
off and the potentiostat is inactive.
In a typical experimental sequence, the Cell LED will be off between experiments and during any open circuit
potential measurements. It will glow yellow whenever the cell is polarized.
Overload LED
The Overload LED is normally unlighted. When it glows red, this indicates that some circuit in the Reference
600 has exceeded its normal operating limit. Conditions that generate Overloads include:
•
The absolute value of the differential electrometer output voltage (the difference in voltage between
the Working and Reference leads) exceeds 10 volts. This condition is known as an E Overload.
•
The control amplifier has lost control of the cell. The absolute value of the cell current may be trying to
exceed ±600 mA, or the absolute value of the counter electrode voltage may be trying to exceed
±22 volts. Either condition will be called a Control Overload.
•
The absolute value of the cell current has exceeded full scale on the current range presently in use.
This condition is known as an I Overload.
Transient (temporary) overloads during an experiment in which the cell voltage or current is being stepped or
swept are often normal. In most cases, they do not indicate a system or instrument malfunction.
Consider the case of an infinitely fast voltage step into a perfect capacitor. In theory, charging the capacitor
requires an infinite current. The current spike seen at each step in a stepped voltage waveform can easily light
the Overload LED. The current spike will normally decay to near zero before the actual current and voltage
readings are taken.
Overload indications when the cell is being connected or disconnected are common and usually do not
indicate a problem. Overloads can also be seen when one of the cell leads is disconnected from the other cell
leads, even though the cell is off. Again, this does not indicate a problem.
6-2
Chapter 6 -- Panel Indicators and Connectors--Rear Panel
A steadily glowing Overload LED during an experiment most likely indicates a problem is occurring. Possible
causes include:
•
One of the cell leads is disconnected (this is the most common cause),
•
a gas bubble in the cell is blocking one of the electrodes,
•
the potentiostat could be oscillating (see the next chapter).
Note
As described above, a glowing red Overload LED does not necessarily indicate a system
malfunction. The Overload LED can light when one or more cell leads are disconnected,
without indicating a problem with the system. The Overload LED can often light
momentarily during a swept or stepped experiment. The only Overload LED indication
that definitely points towards a problem is a continuously glowing Overload LED during
an experiment.
Rear Panel
The rear panel contains one switch and a large number of connectors. A picture of the Reference 600 rear
panel can be seen in Figure 4 - 2.
Power In Jack
The Reference 600 derives all its power from +24 volts DC input through the Power In jack. The input current
is less than 3 amps.
We recommend that you always use the external power supply supplied with your Reference 600 to supply DC
power to the instrument. This supply is rated for operation from 100 to 240 volts AC, at frequencies from 47 to
63 Hz. It should therefore be useable worldwide. While a Reference 600 may work with other power
sources, we cannot guarantee it will work to its full specifications.
If you have to use the Reference 600 with a different supply, make sure that the supply is regulated, has an
output between 22 and 26 volts, and supplies 3 amps of load current.
Caution
Power input voltages less than 20 volts or greater than 32 volts can damage the Reference
600’s power supply.
Power Switch
The Power Switch is located just below the Power In jack. It switches the power from this jack to the input of
the Reference 600’s DC-DC converter. All protection circuitry, including the in-rush current limiter, are located
after this switch.
Normally, the DC Power is connected before the Power Switch is turned ON. However, no damage will occur
if this switch is already in the ON position when the DC Power In cable is connected, or the AC power input is
connected to the external power supply.
Chassis Ground
The rear panel Chassis Ground is intended for one use only. When the Reference 600 is used with cells
isolated from earth ground, connecting the chassis ground to earth ground may lower the noise measured in the
system. Note that the chassis of the Reference 600 is connected to Floating Ground. See Chapter 1, for safety
information concerning this connection.
Either a banana plug or the stripped end of a wire can be connected to the Chassis Ground binding post. The
other end of the wire is then connected to earth ground.
6-3
Chapter 6 -- Panel Indicators and Connectors--Rear Panel
A black banana-plug to banana-plug lead has been provided with your Reference 600. You may find it useful
when making this earth ground connection.
USB Port
The USB port on the rear panel of the Reference 600 is a Type B connector as defined in Revision 1.1 and 2.0
of the USB Specification. You use a standard, shielded, Type A/B cable to connect this port to a computer’s
USB port or a USB hub (preferably an externally powered hub). The two ends of a Type A/B cable are
different. The more-rectangular end plugs into the computer and the more-square end plugs into the Reference
6000.
A suitable USB cable was included with your Reference 600 shipment. If this cable is lost, you can replace it
with a cable from your local computer retailer.
The Reference 600 is a High Speed USB 2.0 peripheral, capable of data transfer at 480 Mbits/second. If it is
plugged into a computer port incapable of High Speed operation it will downgrade to USB 1.1 full speed
operation (12 Mbits/second). Obviously data transfer speed will be slower if this occurs.
The Reference 600 USB port is compatible with Revision 1.1 and 2.0 of the USB specification. It supports the
Windows Plug-n-Play mechanism, including dynamic connect/reconnect.
The front panel USB LED should be green whenever a valid computer to Reference 3000 connection has been
made and both the computer and Reference 3000 are fully powered.
Thermocouple Input
The Reference 600 has an input jack for either a J Type or K Type thermocouple, depending upon the date of
manufacture. The ISO standard calls for color-coded mini-thermocouple connections. Black is the color
assigned to J Type thermocouples. Yellow is the color assigned to K Type thermocouples. The mating
connector on your thermocouple should therefore be black if your unit is marked with J Type T/C on the rear of
the instrument, or yellow if your unit is marked with K Type T/C.
Possible uses for temperature measurement in an electrochemical test include:
•
Looking for a temperature rise at end-of-charge on a battery.
•
Measuring ambient temperature prior to a corrosion measurement in the field.
•
Measuring temperature in a cell before making a CV measurement that will be used to calculate
reaction kinetics.
Gamry Instruments chose not to provide a thermocouple with the Reference 600. There is simply too much
variety in the mechanical design of thermocouple probes. Commercial thermocouples designed for
measurement in air, on solid surfaces, and in immersion service are available from a variety of vendors. Make
sure you get the proper type thermocouple as shown on the rear of your Reference 600.
The Reference 600 uses a temperature measurement IC to convert the thermocouple output to a useable
voltage. It outputs a voltage that is nominally 10 mV per degree Celsius. The IC used varies with the type of
thermocouple input. For the J Type thermocouple, the Analog Device AD594A is rated for an accuracy of 3°C.
For the K Type thermocouple, the Analog Device AD597AR is rated for an accuracy of 4°C. The specified
accuracy is only achieved when the Reference 600 is calibrated. The scaling at the A/D converter is ± 3 volts
full scale, or ± 300°C full scale.
The Reference 600 calibration script has an optional section for thermocouple calibration. An ice-water bath
and a beaker of boiling water provide convenient standards for a two-point calibration.
6-4
Chapter 6 -- Panel Indicators and Connectors--Rear Panel
Caution
One side of the thermocouple is connected to the Reference 600’s Floating Ground. An
improper connection to the thermocouple input can compromise the Reference 600’s
ability to float and invalidate data collected on earth grounded cells. A connection to an
non-insulated thermocouple immersed in your electrochemical cell can also cause
erroneous readings.
Misc I/O Connector
The Misc (Miscellaneous) I/O connector is a multipurpose connector. It contains both digital and analog signals
used to interface external devices to the Reference 600.
All of its signals are isolated from both earth ground and the Reference 600’s Floating Ground. The device
connected to this connector establishes a ground reference. This isolation allows the Misc I/O connector to be
connected to earth grounded apparatus, without compromising the Reference 600’s ground isolation.
A full description of this connector can be found in Appendix C of this manual. This appendix includes details
such as connector pin-out, output and input voltage levels and full signal descriptions.
The following list is a short description of the signals in the Misc I/O Connector and their uses:
•
Sync Out and Sync In signal allow two or more Reference 600s to use one data acquisition clock.
•
Four digital outputs can be used to turn on external devices under control of an Explain experimental
control script.
•
Some of Gamry applications assign three of the digital output to control stirring, flow of deaeration gas,
and formation of mercury drops on a mercury drop electrode.
•
Four digital inputs that can be read in an Explain experimental control script.
•
A 12-bit D/A converter used to set “continuously variable” settings, such as electrode rotation rate on a
rotating disk electrode.
•
A 5 volt isolated power supply that can provide up to 50 mA of current for external circuitry.
I Monitor BNC
The I Monitor BNC connector represents the output of the Reference 600’s current measurement circuit. With
the exception of the filtering described below, it is the raw signal. It will be high bandwidth on the less sensitive
current ranges. The effective bandwidth of the current signal falls as you reach the nA and pA current ranges.
IE Stability capacitors further slow the response.
The outer shell of this BNC connector is connected to the Reference 600’s floating ground.
Caution
The shell of the I Monitor BNC is connected to the Reference 600’s Floating Ground.
Connection of this BNC to a piece of earth ground referenced equipment can compromise
the Reference 600’s ability to float and invalidate data collected on earth grounded cells.
Scaling on this signal is ±3 volts for ± the nominal full scale current on the selected current range. Cathodic
currents will cause a positive output voltage. If the software is auto-ranging the current-range selection, this
signal will be discontinuous at each range change.
The I Monitor BNC connector is lightly filtered using an RLC circuit. It has a bandwidth of approximately
3 MHz when connected to a high impedance input. This bandwidth will be further reduced if a coaxial cable is
connected to the BNC. Its output impedance is approximately 200 Ohms in parallel with 220 pF.
6-5
Chapter 6 -- Panel Indicators and Connectors--Rear Panel
E Monitor BNC
The E Monitor BNC connector is the output of the Reference 600’s differential electrometer circuit. With the
exception of the filtering described below, it is buffered representation of the voltage difference between the
white and blue cell cable leads. It has very high bandwidth.
The outer shell of the BNC connector is connected to the Reference 600’s floating ground.
Caution
The shell of the E Monitor BNC is connected to the Reference 600’s Floating Ground.
Connection of this BNC to a piece of earth ground referenced equipment can compromise
the Reference 600’s ability to float and invalidate data collected on earth grounded cells.
The E Monitor BNC connector is lightly filtered using an RLC circuit. It has a bandwidth of approximately
3 MHz when connected to a high impedance input. This bandwidth will be further reduced if a coaxial cable is
connected to the BNC. Its output impedance is approximately 200 Ohms in parallel with 220 pF.
Ext. Sig. In BNC
The External Signal In BNC connector allows you to add a voltage to the Reverence 600’s Signal Generator.
This signal will be summed with the other signal generator sources including the IR DAC, the Scan DAC, and
the DDS output.
The outer shell of the BNC is connected to the Reference 600’s floating ground.
Caution
The shell of the Ext Sig In BNC is connected to the Reference 600’s Floating Ground.
Connection of this BNC to a piece of earth ground referenced equipment can compromise
the Reference 600’s ability to float and invalidate data collected on earth grounded cells.
The signal generator output is usually directly connected to the potentiostat’s input. When the cell is turned on
in potentiostat mode, the feedback is such that a negative signal generator output creates a positive differential
electrometer signal, which corresponds to a negative working electrode versus reference electrode voltage.
The polarity of the External Signal In signal is inverted at the signal generator’s output. As described above, a
negative input signal on this BNC will create a positive change in the working electrode versus reference
electrode voltage. The input impedance of this signal is 3 kΩ in parallel with 15 pF.
Sig Gen Out BNC
The Sign Gen Out BNC connector allows you to monitor the “signal generator” signal being sent from the
Reference 600’s controller board to the potentiostat board. This signal has a high bandwidth. The signal output
range is –15 volts to +15 volts.
The outer shell of the BNC is connected to the Reference 600’s floating ground.
Caution
The shell of the Ext Sig In BNC is connected to the Reference 600’s Floating Ground.
Connection of this BNC to a piece of earth ground referenced equipment can compromise
the Reference 600’s ability to float and invalidate data collected on earth grounded cells.
The Sig Gen Out BNC connector is lightly filtered using an RLC circuit. It has a bandwidth of approximately
3 MHz when connected to a high impedance input. This bandwidth will be further reduced if a coaxial cable is
connected to the BNC. Its output impedance is approximately 200 Ohms in parallel with 220 pF.
6-6
Chapter 6 -- Panel Indicators and Connectors--Rear Panel
Aux In BNC
The Aux In BNC connector allows you to measure a voltage from outside the Reference 600 using the
Reference 600’s internal A/D. The scaling is: ±3 volts in equals ±30000 A/D counts. This is a resolution of 100
µV per bit. The results will be reported in volts. The input is differential (see Appendix D).
The allowed input voltage range is –24 volts to +24 volts. Voltages outside this range could damage the
Reference 600 circuitry.
Consult Appendix D for additional information concerning this connector.
6-7
Chapter 7 -- Stability in Potentiostat Mode--Capacitive Cells and Stability
Chapter 7 -- Stability in Potentiostat Mode
Capacitive Cells and Stability
All potentiostats can become unstable when connected to capacitive cells. The capacitive cell adds phase shift
to the potentiostat's feedback signal (which is already phase shifted). The additional phase shift can convert the
potentiostat's power amplifier into a power oscillator.
To make matters worse, almost all electrochemical cells are capacitive because an electrical double layer forms
next to a conductor immersed in a solution.
Potentiostat oscillation is an AC phenomenon. However, it can affect both AC and DC measurements.
Oscillation often causes excessive noise or sharp DC shifts in the system's graphical output. The Reference 600
Potentiostat can be stable on less sensitive current ranges and unstable on more sensitive current ranges.
Whenever you see sharp breaks in the current recorded on the system, you should suspect oscillation.
The Reference 600 has been tested for stability with cell capacitors between 10 pF and 0.1 F. In all but its
fastest control amp speed setting, it is stable on any capacitor in this range -- as long as the impedance in the
reference electrode lead does not exceed 20 kΩ. With reference electrode impedances greater than 20 kΩ,
the Reference 600 may oscillate. The RC filter formed by the reference electrode impedance and the reference
terminal's input capacitance filters out the high frequency feedback needed for potentiostat stability.
Longer cell cables make the problem worse by increasing the reference terminal's effective input capacitance.
Even when the system is stable (not oscillating), it may exhibit ringing whenever there is a voltage step applied
to the cell. The Reference 600's D/A converters routinely apply steps, even when making a pseudo-linear
ramp. While this ringing is not a problem with slow DC measurements, it can interfere with faster
measurements. The steps taken to eliminate potentiostat oscillation also help to minimize ringing.
7-1
Chapter 7 -- Stability in Potentiostat Mode--Improving Potentiostat Stability
Improving Potentiostat Stability
There are a number of things that you can do to improve an unstable or marginally stable Reference 600
potentiostat/cell system. This list is not in any particular order. Any or all of these steps may help.
•
Slow down the potentiostat. The Reference 600 has five control amplifier speed settings, which can be
selected in software. Slower settings are generally more stable.
•
Increase the Reference 600's I/E stability setting. The Reference 600 includes three capacitors that can
be paralleled with its I/E converter resistors. These capacitors are connected to relays that are under
software control. Contact your local Gamry Instruments' representative for more information
concerning changes in these settings.
•
Lower the reference electrode impedance. Make sure that you don't have a clogged reference
electrode junction. Avoid asbestos fiber reference electrodes and double-junction electrodes. Avoid
small diameter Luggin capillaries. If you do have a Luggin capillary, make sure that the capillary’s
contents are as conductive as possible.
•
Add a capacitively coupled low impedance reference element in parallel with your existing reference
electrode. The classic fast combination reference electrode is a platinum wire and a junction isolated
SCE. See Figure 7-1. The capacitor insures that DC potential comes from the SCE and AC potential
from the platinum wire. The capacitor value is generally determined by trial and error.
Figure 7-1
Fast Combination Reference Electrode
White
Cell Lead
100 pF to 10 nF
SCE
Platinum
Electrolyte
7-2
Chapter 7 -- Stability in Potentiostat Mode--Improving Potentiostat Stability
•
Provide a high frequency shunt around the cell. A small capacitor between the red and white cell
leads allows high frequency feedback to bypass the cell. See Figure 7-2. The capacitor value is
generally determined by trial and error. One nF (1000 pF) is a good starting point.
In a sense, this is another form of an AC coupled low impedance reference electrode. The counter
electrode is the low impedance electrode, eliminating the need for an additional electrode in the
solution.
Figure 7-2
High Frequency Shunt
Red
100 pF to 10 nF
White
Reference
Green
Working
7-3
Counter
Chapter 7 -- Stability in Potentiostat Mode--Improving Potentiostat Stability
•
Add resistance to the counter electrode lead. See Figure 7-3. This change lowers the effective
bandwidth of the control amplifier. As a rule of thumb, the resistor should be selected to give one
volt of drop at the highest current expected in the test being run. For example, if you expect your
highest current to be around 1 mA, you can add a 1 kΩ resistor.
This resistor has no effect on the DC accuracy of the potentiostat. It can create problems in
high-speed experiments such as fast CV scans or EIS, which need high bandwidth.
Figure 7-3
Resistor Added for Stability
Red
Resistor
White
Reference
Green
Working
7-4
Counter
Chapter 8 -- Measurement of Small Signals--Overview
Chapter 8 -- Measurement of Small Signals
Overview
The Reference 600 is a very sensitive scientific instrument. It can theoretically resolve current changes as
small as 1 femoamp (1 x 10-15 amps). To place this current in perspective, 1 fA represents the flow of about
6000 electrons per second!
The small currents measured by the Reference 600 place demands on the instrument, the cell, the cables
and the experimenter. Many of the techniques used in higher current electrochemistry must be modified
when used to measure pA currents. In many cases, the basic physics of the measurement must be
considered.
This chapter will discuss the limiting factors controlling low current measurements. It will include hints on
cell and system design. The emphasis will be on EIS (Electrochemical Impedance Spectroscopy), a highly
demanding application for the Reference 600.
Measurement System Model and Physical Limitations
To get a feel for the physical limits implied by very sensitive current measurements, consider the equivalent
circuit shown in Figure 8-1. We are attempting to measure the cell impedance given by Zcell.
This model is valid for analysis purposes even though the real Reference 600 circuit topology differs
significantly.
In Figure 8-1:
Es
Zcell
Icell
Rm
Is an ideal signal source
Is the unknown cell impedance
Is the “real” cell current
Is the current measurement circuit's current measurement resistance
Rshunt
Cshunt
Cin
Rin
Iin
Is an unwanted resistance across the cell
Is an unwanted capacitance across the cell
Is the current measurement circuit's stray input capacitance
Is the current measurement circuit's stray input resistance
Is the measurement circuit's input current
In the ideal current measurement circuit Rin is infinite while Cin and Iin are zero. All of the cell current, Icell,
flows through Rm.
With an ideal cell and voltage source, Rshunt is infinite and Cshunt is zero. All the current flowing into the
current measurement circuit is due to Zcell.
The voltage developed across Rm is measured by the meter as Vm. Given the idealities discussed above,
one can use Kirchoff's and Ohms law to calculate Zcell:
Zcell = Es * Rm / Vm
8-1
Chapter 8 -- Measurement of Small Signals--Measurement System Model and Physical Limitations
Figure 8-1
Equivalent Measurement Circuit
R shunt
C shunt
Icell
Rm
R in
C in
Unfortunately technology limits high impedance measurements because:
•
Current measurement circuits always have non-zero input capacitance, i.e. Cin > 0.
•
Infinite Rin cannot be achieved with real circuits and materials.
•
Amplifiers used in the meter have input currents, i.e. Iin > 0.
•
The cell and the potentiostat create both a non-zero Cshunt and a finite Rshunt.
Additionally, basic physics limits high impedance measurements via Johnson noise, which is the inherent
noise in a resistance.
Johnson Noise in Zcell
Johnson noise across a resistor represents a fundamental physical limitation. Resistors, regardless of
composition, demonstrate a minimum noise for both current and voltage, per the following equations:
E = (4 k T R δF)1/2
I = (4 k T δF / R)1/2
Where;
k = Boltzman's constant 1.38x 10-23 J/oK
T = temperature in oK
δF = noise bandwidth in Hz
R = resistance in ohms.
8-2
Chapter 8 -- Measurement of Small Signals--Measurement System Model and Physical Limitations
For purposes of approximation, the Noise bandwidth, δF, is equal to the measurement frequency. Assume
a 1011 ohm resistor as Zcell. At 300 oK and a measurement frequency of 1 Hz this gives a voltage noise of
41 µV rms. The peak-to-peak noise is about 5 times the rms noise. Under these conditions, you can make
a voltage measurement of ± 10 mV across Zcell with an error of about ± 0.4%. Fortunately, an AC
measurement can reduce the bandwidth by integrating the measured value at the expense of additional
measurement time. With a noise bandwidth of 1 mHz, the voltage noise falls to about 1.3 µV rms.
Current noise on the same resistor under the same conditions is 0.41 fA. To place this number in
perspective, a ± 10 mV signal across this same resistor will generate a current of ± 100 fA, or again an error
of up to ± 0.4%. Again, reducing the bandwidth helps. At a noise bandwidth of 1 mHz, the current noise
falls to 0.013 fA.
With Es at 10 mV, an EIS system that measures 1011 ohms at 1 Hz is about 2 ½ decades away from the
Johnson noise limits. At 10 Hz, the system is close enough to the Johnson noise limits to make accurate
measurements impossible. Between these limits, readings get progressively less accurate as the frequency
increases.
In practice, EIS measurements usually cannot be made at high enough frequencies that Johnson noise is the
dominant noise source. If Johnson noise is a problem, averaging reduces the noise bandwidth, thereby
reducing the noise at a cost of lengthening the experiment.
Finite Input Capacitance
Cin in Figure 8-1 represents unavoidable capacitances that always arise in real circuits. Cin shunts Rm,
draining off higher frequency signals, limiting the bandwidth that can be achieved for a given value of Rm.
This calculation shows at which frequencies the effect becomes significant. The frequency limit of a current
measurement (defined by the frequency where the phase error hits 45o) can be calculated from:
fRC = 1/ ( 2 π f RmCin )
Decreasing Rm increases this frequency. However, large Rm values are desirable to minimize the effects of
voltage drift and voltage noise in the I/E converter’s amplifiers.
A reasonable value for Cin in a practical, computer controllable, low current measurement circuit is 20 pF.
For a 6 nA full scale current range, a practical estimate for Rm is 107 ohms.
fRC = 1/ 6.28 (1x107 )(2x10-12) ≈ 8000 Hz
In general, one should stay two decades below fRC to keep phase shift below one degree. The uncorrected
upper frequency limit on a 6 nA range is therefore around 80 Hz.
One can measure higher frequencies using the higher current ranges (i.e. lower impedance ranges) but this
would reduce the total available signal below the resolution limits of the "voltmeter". This then forms one
basis of statement that high frequency and high impedance measurements are mutually exclusive.
Software correction of the measured response can also be used to improve the useable bandwidth, but not
by more than an order of magnitude in frequency.
Leakage Currents and Input Impedance
In Figure 8-1, both Rin and Iin affect the accuracy of current measurements. The magnitude error due to
Rin is calculated by:
Error = 1- Rin/(Rm+Rin)
For an Rm of 107 ohms, an error < 1% demands that Rin must be greater than 109 ohms. PC board
leakage, relay leakage, and measurement device characteristics lower Rin below the desired value of
infinity.
8-3
Chapter 8 -- Measurement of Small Signals--Measurement System Model and Physical Limitations
A similar problem is the finite input leakage current Iin into the voltage measuring circuit. It can be leakage
directly into the input of the voltage meter, or leakage from a voltage source (such as a power supply)
through an insulation resistance into the input. If an insulator connected to the input has a 1012 ohm
resistance between +15 volts and the input, the leakage current is 15 pA. Fortunately, most sources of
leakage current are DC and can be tuned out in impedance measurements. As a rule of thumb, the DC
leakage should not exceed the measured AC signal by more than a factor of 10.
The Reference 600 uses an input amplifier with an input current of around 1 pA. Other circuit
components may also contribute leakage currents. You therefore cannot make absolute current
measurements of very low pA currents with the Reference 600. In practice, the input current is
approximately constant, so current differences or AC current levels of less than one pA can often be
measured.
Voltage Noise and DC Measurements
Often the current signal measured by a potentiostat shows noise that is not the fault of the current
measurement circuits. This is especially true when you are making DC measurements. The cause of the
current noise is noise in the voltage applied to the cell.
Assume that you have a working electrode with a capacitance of 40 µF. This could represent a 1 cm2
polished bare metal immersed in an electrolyte solution. You can roughly estimate the capacitance of the
electrical double layer formed by a metal/electrolyte interface as 20 µF/cm2. The area is the microscopic
area of the surface, which is larger than the geometric area, because even a polished surface is rough. The
impedance of this 40 µF electrode, assuming ideal capacitive behavior, is given by:
Z = 1/jωC
At sixty Hertz, the impedance magnitude is about 66 Ω.
Apply an ideal DC potential across this ideal capacitor and you get no DC current.
Unfortunately, all potentiostats have noise in the applied voltage. This noise comes from the instrument
itself and from external sources. In many cases, the predominant noise frequency is the AC power line
frequency.
Assume a realistic noise voltage, Vn, of 10 µV (this is lower than the noise level of most commercial
potentiostats). Further, assume that this noise voltage is at the US power line frequency of 60 Hz. It will
create a current across the cell capacitance:
I = Vn/Z ≈ 10 x 10-6/ 66 ≈ 150 nA
This rather large noise current will prevent accurate DC current measurement in the low nA or pA ranges.
In an EIS measurement, you apply an AC excitation voltage that is much bigger than the typical noise
voltage, so this is not a factor.
8-4
Chapter 8 -- Measurement of Small Signals--Hints for System and Cell Design
Shunt Resistance and Capacitance
Non-ideal shunt resistance and capacitance arise in both the cell and the potentiostat. Both can cause
significant measurement errors.
Parallel metal surfaces form a capacitor. The capacitance rises as either metal area increases and as the
separation distance between the metals decreases.
Wire and electrode placement have a large effect on shunt capacitance. If the clip leads connecting to the
working and reference electrodes are close together, they can form a significant shunt capacitor. Values of
1 to 10 pF are common. This shunt capacitance cannot be distinguished from "real" capacitance in the cell.
If you are measuring a paint film with a 100 pF capacitance, 5 pF of shunt capacitance is a very significant
error.
Shunt resistance in the cell arises because of imperfect insulators. No material is a perfect insulator (one
with infinite resistance). Even Teflon, which is one of the best insulators known, has a bulk resistivity of
about 1012 ohms•m. Worse yet, surface contamination often lowers the effective resistivity of good
insulators. Water films can be a real problem, especially on glass.
Shunt capacitance and resistance also occur in the potentiostat itself. The Reference 600 Potentiostat
Mode specifications in Appendix A contain equivalent values for the potentiostat's Rshunt and Cshunt. These
values can be measured by an impedance measurement with no cell.
In most cases, the cell's shunt resistance and capacitance errors are larger than those from the potentiostat.
Hints for System and Cell Design
The following hints may prove helpful.
Faraday Shield
A Faraday shield surrounding your cell is mandatory for very low-level measurements. It reduces both
current noise picked up directly on the working electrode and voltage noise picked up by the reference
electrode.
A Faraday shield is a conductive enclosure that surrounds the cell. The shield can be constructed from
sheet metal, fine mesh wire screen, or even conductive paint on plastic. It must be continuous and
completely surround the cell. Don't forget the areas above and below the cell. All parts of the shield must
be electrically connected. You will need an opening in the shield large enough to allow a cell cable to
enter the shield.
The shield must be electrically connected to the Reference 600's floating ground terminal.
An additional connection of both the shield and the Reference 600 floating ground to an earth ground may
also prove helpful.
NOTE
Only connect the Reference 600 ground to earth ground if all conductive cell
components are well isolated from earth ground. A glass cell is usually well isolated.
An autoclave is generally not well isolated.
8-5
Chapter 8 -- Measurement of Small Signals--Hints for System and Cell Design
Avoid External Noise Sources
Try to keep your system away from electrical noise sources. Some of the worst are:
•
Fluorescent lights
•
Motors
•
Radio transmitters
•
Computers and computer monitors
Try to avoid AC powered or computerized apparatus within your Faraday shield.
Cell Cable Length and Construction
The Reference 600 is shipped with a 60 cm shielded cell cable. We also offer extended length cables and
unshielded cables as extra cost options.
Cell cables longer than 1 meter will result in degraded instrument performance. Increased noise and
decreased stability both can occur. However, with most cells, the instrument will work acceptably with an
extended cell cable, so our advice is go-ahead and try it. As a rule, you should not attempt to use current
interrupt IR compensation with cell cables longer than 5 meters.
We do not recommend that you use the Reference 600 with any cables not supplied by Gamry
Instruments. The Reference 600 cable is not a simple cable like a typical computer cable. The Reference
600 cable includes a number of individually shielded wires contained within an overall shield. We pay
careful attention to issues such as shield isolation, isolation resistance, and capacitance.
If you do need a special cable, contact us with your requirements.
Lead Placement
Many experiments with the Reference 600 involve cells with small capacitances, the value of which may be
important.
In these cases, the capacitance between the Reference 600's cell leads can result in an error. The
Reference 600 alligator clips can have 10 pF or more of mutual capacitance if they are run alongside each
other.
If you wish to avoid excessive capacitance:
•
Place the leads as far apart as possible. Pay special attention to physical separation between
the working electrode/ working sense leads and the counter/ counter sense/ reference
electrode leads.
•
Have the leads approach the cell from different directions.
•
Remove the alligator clips from the leads. In extreme cases you can replace the banana plugs
and pin jack with smaller connectors. If you do so, be careful not to compromise the isolation
between the center conductor and the shield.
The cell leads must not be moved during an experiment measuring small currents. Both microphonic and
triboelectric effects can create spurious results when the cell cables are moved.
8-6
Chapter 8 -- Measurement of Small Signals--Hints for System and Cell Design
Cell Construction
If you need to measure small currents or high impedances, make sure that your cell construction does not
limit your response.
A cell where the resistance between the electrodes is only 1010 ohms cannot be used to measure 1013
ohm impedances. In general, glass and Teflon are the preferred cell construction materials. Even glass may
be a problem when it is wet.
You also must worry about Cshunt. Make the "inactive" portion of your electrodes as small as possible.
Avoid placing electrodes close together or parallel with each other if you are measuring high impedances.
Reference Electrode
Keep your reference electrode impedance as low as possible. High impedance reference electrodes can
cause potentiostat instability and excessive voltage noise pickup.
Try to avoid:
•
Narrow bore or Vycor tipped Luggin capillaries.
•
Poorly conductive solutions - especially in Luggin capillaries.
•
Asbestos thread and double junction reference electrodes.
Reference electrodes often develop high impedances as they see use. Anything that can clog the isolation
frit can raise the electrode impedance. Avoid using saturated KCl based references in perchlorate ion
solutions
Instrument Settings
There are several things to remember in setting up a very sensitive experiment.
•
In EIS, use the largest practical excitation. Don't use a 10 mV excitation on a coated specimen
that can handle 100 mV without damage.
•
Avoid potentials where large DC currents flow. You cannot measure 1pA of AC current on top
of 1 mA of DC current.
EIS Speed
In EIS, do not expect the Reference 600 to measure 1010 ohm impedances at 1 kHz. Many of the factors
listed above limit the performance.
As a rule of thumb, the product of Impedance, Z, times frequency, f, should be less than 109 ΩHz for good
EIS measurements with a Reference 600.
Z · f < 109 ΩHz
Ancillary Apparatus
Do not use the Reference 600 with ancillary apparatus connected directly to any of the cell leads.
Ammeters and voltmeters, regardless of their specifications, almost always create problems when connected
to the Reference 600 cell leads.
8-7
Chapter 8 -- Measurement of Small Signals--Floating Operation
Floating Operation
The Reference 600 is capable of operation with cells where one of the electrodes or a cell surface is at
earth ground. Examples of earth grounded cells include: autoclaves, stress apparatus, pipelines, storage
tanks and battleships. The Reference 600's internal ground is allowed to float with respect to earth ground
when it works with these cells, hence the name floating operation.
Instrument performance can be substantially degraded when the Reference 600 is operated in a floating
mode. The instrument specifications only apply on isolated cells with the Reference 600 earth ground
referenced (not floating).
Special precautions must be taken with the cell connections when the Reference 600 must float. Make
sure that all the cell connections are isolated from earth ground. In this case, you must disconnect the
chassis ground terminal of the Reference 600 from earth ground.
Finally, ancillary apparatus connected to the Reference 600 must be isolated. External voltmeters,
ammeters, FRA's etc. must be isolated. This includes devices connected to the monitor connectors located
on the Reference 600 rear panel.
8-8
Appendix A -- Reference 600 Specifications--
Appendix A -- Reference 600 Specifications
All specifications are at an ambient temperature of 25 °C, with the Reference 600 powered using the
external power supply shipped with the unit, a standard shielded 60 cm cell cable, and the cell enclosed in
a Faraday shield. All specifications are after software calibration.
A numbered note qualifies many of the specifications. Many of these notes describe the method used to
measure a specification. The notes are found at the end of this appendix.
All specifications are subject to change without notice.
Control Amplifier
Compliance Voltage
Min
± 22
volts
Note 1
Output Current
Min
± 600
mA
Note 2
Unity Gain Bandwidth
Typ
980, 260, 40, 4.0, 0.4
kHz
Notes 3, 4
Slew Rate
Typ
10, 4.5, 0.6, 0.06, 0.006
V/µsec
Notes 3, 4
Max Input Voltage
Min
±9
volts
Note 5
Input Current
Max
10
pA
Notes 5, 6
Input Resistance
Differential (between inputs)
Common Mode (input to ground)
Input Capacitance
Differential (between inputs)
Common Mode (input to ground)
Bandwidth (-3 dB)
Typ
TΩ
Note 7
pf
Note 7
MHz
Note 7
Differential Electrometer
CMMR
DC to 100 kHz
100 kHz to 1 MHz
100
1
Typ
Min
0.2
12
15
Min
Note 8
80
60
Voltage Measurement
A/D Full Scale Ranges
Typ
±12.0, ± 3.0
Volts
Resolution
Typ
400, 100
µV/bit
Zero Offset Error
Max
1
mV
Note 10
Gain Error
Max
0.2
%
Note 10
Offset Range
Typ
± 10
Volts
Post- Offset Gain
Typ
1x, 10x, 100x
9-1
Note 9
Appendix A -- Reference 600 Specifications--
Current to Voltage Converter
Maximum Full Scale Range
600
mA
Note 11
Minimum Full Scale Range
pA
fA
mV at
full scale
Volts
full scale
pA
Note 11
Voltage across Rm
Typ
60
600 (after x100 gain)
120
Output Voltage (at BNC and ADC in)
Typ
3.0
Input Offset Current
Max
10
Range Zero Offset
Max
0.05
Gain Tolerance
600 mA to 6 nA ranges
600 pA range
60 pA
Zero drift
Max
Bandwidth
600 mA to 600 µA ranges
60 µA range
6 µA range
Typ
Typ
0.2
0.75
1.5
0.03
% of
range
% of
reading
MHz
Current Measurement
Typ
0.00333…
Offset Range
Typ
± 100
Post- Offset Gain
Typ
1x, 10x, 100x
Accuracy
Typ
Dominated by current to voltage error
(see above)
9-2
Note 13
Note 13
Note 13
% FS /°C Note 14
> 10
> 1.5
> 0.15
Resolution
Note 12
% FS
/bit
% of
range
Note 15
Appendix A -- Reference 600 Specifications--
Potentiostatic Mode
Applied Voltage Range
Min
± 11
volts
Accuracy
DC zero offset
Gain
DC Bias
Max
Notes 5, 6
Typ
1
0.2
±8
mV
% setting
volts
Scan DAC ranges
Typ
± 6.4, ± 1.6, ± 0.4
volts
Drift
Max
< 20
µV/°C
Note 17
Noise and Ripple
1 Hz to 1 kHz
1 Hz to 200 kHz
Typ
µV rms
Note 18
Note 16
10
20
Galvanostatic Mode
Maximum Full Scale Current
± 600
mA
Note 11
Minimum Full Scale Current
60
pA
Note 11
Accuracy
Dominated by current to voltage
converter accuracy shown above
± 3.0 volts
Sig Gen Voltage for Full Scale Current
Auxiliary A/D Input (see Appendix D)
Range (differential)
Typ
±3
volts
Input voltage range
(either input)
Gain Error
Max
± 3.6
volts
Max
0.2
%
100
10
kΩ
GΩ
Input Impedance
a) as shipped
b) re-jumpered for high Z input
Typ
Note 19
Auxiliary D/A Output
Range
Typ
0 to 4.096
volts
Resolution
Typ
1
mV
0 to 45
°C
90 (non-condensing)
%
Storage and Shipping Temperature
-25 to 75
°C
Maximum Shipping acceleration
30
G
Environmental
Operating Temperature Range
Relative Humidity
Max
9-3
Appendix A -- Reference 600 Specifications--
General
Power Input Voltage
Range 22 to 26
volts
Power
Max
W
50
Leakage Current
(floating, earthed Working Electrode)
Dimensions
Note 20
Max
10 x 20 x 30
cm
Note 21
Weight
Max
2.5
kg
Note 21
Dimensions of External Power Adapter
Max
7.5 x 3.5 x 15
cm
Note 22
Weight of External Power Adapter
Max
400
grams
Note 22
± 1 nA
NOTES:
1. Measured in galvanostatic mode with a high wattage 200 Ω load connected from counter electrode
lead to the working electrode lead. The compliance voltage is measured using an external voltmeter
across the 200 Ω load. Under these conditions, the output current is approximately 115 mA.
2. Measured with a precision 4-terminal 2 Ω load, in potentiostatic mode.
3. Unity gain bandwidth and slew rate are correlated. Each has five settings, with the highest slew-rate
occurring at the highest bandwidth, down to the lowest slew-rate occurring at lowest bandwidth. Both
are measured with 20 kΩ between counter and reference and 100 Ω between the reference and the
working and working sense leads
4. Measured with an external function generator connected to the Ext Sig In BNC.
5. The Differential Electrometer Amps are Analog Devices AD8065 Op amps specially selected for low
Vos drift versus temperature. These amps have a dual input stage, with a JFET input over most of their
input range and a bipolar transistor input at input voltages greater than + 9.5 volts. They are only a
high impedance buffer from –12 volts to +9.5 volts, though they are a unity gain buffer over their
whole input voltage range.
6. The input current of the JFET inputs on the AD8065s is less than 6 pA. When the Bipolar input is
operative, the input current can be in the microamps. The specified current is only applicable at
voltages of 2 volts or less.
7. The differential impedance is measured between the Reference and Work Sense inputs. This is the
impedance you measure when you record the EIS spectrum of an infinite impedance cell.
There is also a common mode resistance and capacitance associated with the differential electrometer
inputs. These values tell you how much the electrometer response is modified by a resistance in series
with the source.
8. The bandwidth is for a sine-wave source with a 50 Ω output impedance driving either input. The
bandwidth is well in excess of this specification, which is limited by the measurement equipment used
in testing the Reference 600.
9. CMRR is common mode rejection ratio. It specifies the ability of the differential electrometer to reject
signals connected to both inputs. The CMRR is measured driving both inputs with a sine-wave source
with a 50 Ω output impedance, and measuring the error as a function of frequency. Resistance in
either input will cause a loss of CMRR.
10. Voltage measurement is actually performed with a ±3 volt signal input to the ADC signal chain. A ÷4
attenuator divides down higher voltage electrometer outputs so they fit into a ±3 volt input, thus
making a ±12 volt full scale range.
9-4
Appendix A -- Reference 600 Specifications--
11. The total error in a voltage measurement is:
Error = Zero Offset Error + Gain Error * Voltage
For a 1 volt signal the error can be as high as 3 mV.
12. There are 11 hardware current ranges, separated in sensitivity by decades. The ranges are 60 pA, 600
pA, 6 nA, … 60 mA, 600 mA full scale. The x10 and x100 gains add two virtual ranges of 6 pA and
600 fA full scale.
13. The voltage across the current measurement resistor, Rm, is as shown. Slightly higher voltages may be
seen at the working electrode terminal on the cell cable, since the cable has both resistive and
inductive impedance.
14. The total error in a current measurement is:
Error = Input Current Offset + Range Zero Offset * FS Current + Gain Tolerance * Measured Current
For small currents (pA) the first term is usually dominant.
For large currents (uA), the first term can usually be ignored.
The units for the error are amps.
15. Drift can be approximated by simple drift in the Range Zero Error. In reality all three terms in the
equation above can have drift.
16. The Current to Voltage converter bandwidth is a function of the current range, the cell cable, and the
IEStability setting.. The bandwidth can be very low on very sensitive ranges. Longer cell cables add
capacitance and slow the current measurement.
17. The total error in a voltage setting is:
Error = DC Zero Offset + Gain * Voltage Setting
For a 1 volt signal the error can be as high as 3 mV.
18. This specification is guaranteed by design. It is not tested.
19. This specification is measured by applying zero voltage across a 1 Ω resistor and measuring current
noise on the 600 µA scale. 1 µV of voltage noise will create a current of 1 µA. The filters in the ADC
Chain for the I Signal are used to limit the bandwidths as shown in the spec.
20.
21.
22.
23.
Signal averaging via Gamry’s DSP mode will further reduce the measured noise.
See Appendix D.
Isolation quality has both DC factors and AC factors (predominately at the 300 kHz power supply
frequency). Only the DC leakage current is shown here. Consult Gamry’s technical support for
additional information.
Excluding external power adapter and any cables supplied with unit.
Excluding removable line cord.
9-5
Appendix B -- Reference 600 Cell Connector--
Appendix B -- Reference 600 Cell Connector
Chapter 5 describes the connections between a cell cable and an electrochemical cell. This appendix
describes the other end of the cell cable.
Multiple pins assigned to the same signal are connected together on the Reference 600’s Potentiostat
board. If you need to connect this signal outside the Reference 600, you need a wire connected to any
one of the D connector pins.
Table B-1
Cell Connector
Pin(s)
1
Signal Name
Working
Sense
2, 14
WS Shield
3, 4, 15, 17
Reference
Shield
Ground
5, 7, 10, 11,
18, 19, 22,
24
6
Counter
Sense
8
CBL_ID1
9
CBL_ID2
12, 25
Work
Shield
Working
Electrode
Reference
Electrode
13
16
20
CBL_ID0
21
CBL_ID3
23
Counter
Electrode
Use
Connected to the working electrode in most cases (see Chapter 5). This lead
has a 261 Ohm resistor in the cell end of the cable. Custom cell cables are
likely to require a similar resistor.
The shield for the working sense input. Driven to the same potential as Pin
1. Left open at the cell end of the cell cable.
The shield for the reference electrode input. Driven to the same potential as
Pin 16. Left open at the cell end of the cell cable.
The potentiostat's floating ground. Can be used to shield the cell if very low
currents need to be measured. Also used as a shield for the counter
electrode cable.
With a Reference 600, used to sense the potential of the counter electrode.
Allows accurate ZRA mode even with significant cell current through counter
lead’s resistance.
One of 4 cable ID bits. Used to identify the type of cell cable attached to the
unit. Pull to a logic High through a resistor. Ground to set the bit low.
One of 4 cable ID bits. Used to identify the type of cell cable attached to the
unit. Pull to a logic High through a resistor. Ground to set the bit low.
The shield for the working electrode input. Connected to Floating Ground .
Left open at the cell end of the cell cable.
Connected to the working electrode. The cell current flows through this pin.
Connected to the reference electrode in most cases (see Chapter 5). This
lead has a 261 Ohm resistor in the cell end of the cable. Custom cell cables
are likely to require a similar resistor.
One of 4 cable ID bits. Used to identify the type of cell cable attached to the
unit. Pull to a logic High through a resistor. Ground to set the bit low.
One of 4 cable ID bits. Used to identify the type of cell cable attached to the
unit. Pull to a logic High through a resistor. Ground to set the bit low.
Connected to the cell's counter electrode. The cell current flows through this
connection.
Caution
Designing cell cabling for a 1 MHz potentiostat is not a trivial task. Gamry Instruments does not
recommend user designed cables (except as a last resort). In many cases we can build a custom cable to
meet your specific needs. We’ll also be happy to discuss your cabling requirements and give you assistance
if you must you design and build your own cell cable.
10 - 1
Appendix C -- Misc I/O Connector--
Appendix C -- Misc I/O Connector
This connector contains a number of signals, used to interface the Reference 600 to external apparatus. It
is the miniature 15 pin female D shaped connector on the rear panel of the Reference 600. Be careful, the
ground on this connector is not the Reference 600 floating ground.
The auxiliary analog output, derived from a D/A converter, is on this connector. The scaling is normally 1
mV per bit, for a 0 to 4.096 volt full-scale range.
The pin out of this connector is shown in Table C-1.
Table C-1
Miscellaneous I/O Connector
Pin
1
2
3
Name
Analog Output High
Analog Output Low
Sync In
4
Sync Out
5
6
7
8
9
10
11
12
13
14
15
no connection
Ground
Digital Out 0
Digital Out 1
Digital Out 2
Digital Out 3
Digital In 0
Digital In 1
Digital In 2
Digital In 3
+5 Volts
Use
The auxiliary output signal (DAC output).
The auxiliary output ground connection (ground)
Used in slave mode – starts data acquisition
2.2 kΩ input impedance
A TTL pulse output before the start of a data point
330 Ω output impedance
Digital ground
A TTL compatible digital output- 330 Ω output impedance
A TTL compatible digital output- 330Ω output impedance
A TTL compatible digital output- 330Ω output impedance
A TTL compatible digital output- 330Ω output impedance
A TTL compatible digital input- 2.2 kΩ input impedance
A TTL compatible digital input- 2.2 kΩ input impedance
A TTL compatible digital input- 2.2 kΩ input impedance
A TTL compatible digital input- 2.2 kΩ input impedance
Power- 50 mA maximum current
11 - 1
Appendix D -- Auxiliary A/D Input Characteristics--Jumper Identification
Appendix D -- Auxiliary A/D Input Characteristics
The Controller board used in the Gamry Instruments Reference 600 Potentiostat has jumpers or switches
that configure the input circuitry used for the Aux A/D function. Early units have jumpers and later units
have CMOS switches set using software. The changeover occurred in 2009.
We usually ask that you return your Reference 600 to Gamry Instruments if you need to change the
hardware jumpers. This information is provided so a qualified service technician can change the Aux A/D
input jumpers in the field.
The CMOS switches are set using a function call in an Explain script. Once the CMOS switches are set,
they remain in the selected position until another script resets them. Note that the settings will return to
their default values on reset or Power Up of the Reference 600.
Call or Email your local Gamry representative if you need to change your Auxiliary A/D input characteristics
and you are uncertain which type of control board you have.
Jumper Identification
The three jumpers that configure the Aux A/D input are in a cluster located at the upper right side of the
Controller Card. See the figure below for jumper locations.
12 - 1
Appendix D -- Auxiliary A/D Input Characteristics--
Figure D-1
Auxiliary A/D Input Configuration Jumpers
View of Reference600 Controller Board
Filter Jumper
Input Z Jumpers
Input Impedance Selection
Two jumpers are associated with the input impedance – J902 and J903. With J902 and J903 installed, the
Aux A/D input has 100 kΩ input impedance. This is the default setting. With the jumpers installed, the
potentiostat can be calibrated without a cable on the input BNC connector.
With both J902 and J903 removed, the Aux A/D input impedance is 10 GΩ (typically). This setting is
suitable for use with a high impedance source such as a reference electrode. If you have removed these
jumpers, do not calibrate the potentiostat unless you have a cable connecting both Aux A/D inputs to
floating ground.
The CMOS switch shorts the circuit nodes connected by these jumpers. As with the jumpers, in the Low
Impedance setting, the input impedance is set to 100 kΩ. In the high impedance setting, the CMOS
switches are opened increasing the input impedance to about 10 GΩ.
12 - 2
Appendix D -- Auxiliary A/D Input Characteristics--Bandwidth Selection
Bandwidth Selection
J900 (or on some boards J901) controls the bandwidth of the Aux A/D input. With J900 (or J901) removed,
there is no filtering on this input and the –3 dB bandwidth is greater than 300 kHz.
With J900 (or J901) in place (the default setting), a single pole RC filter is used to limit noise into the A/D.
The nominal cutoff frequency of this filter is 20 Hz.
Note that source impedances greater than 1 kΩ will appreciably lower this cutoff frequency. When the
Aux A/D input is driven by a source with an output impedance of 1 MΩ, the frequency cutoff will be less
than 0.25 Hz.
The CMOS switch performs the same function as the jumper.
Aux A/D Specifications
Range
Input Impedance
±3.276 volts
100 kΩ (approx)
or
Low Impedance Selected
10 GΩ (typical)
High Impedance Selected
Input Bias Current
< 10 nA
High Impedance selected
Filter Cutoff
20 Hz ± 20%
With Low Bandwidth selected
Function Call to Set the Aux A/D BNC Characteristics
The CMOS switch is set using an Explain function call. The syntax of this call is:
Pstat.SetAuxBNCSettings (Impedance, Bandwidth)
Both variables passed to the function are Booleans (with a value of TRUE or FALSE).
The following definitions can be used to make a script that calls this function more readable.
#define SETAUXBNCSETTINGS_IMPEDANCE_HIGH TRUE
#define SETAUXBNCSETTINGS_IMPEDANCE_LOW FALSE
#define SETAUXBNCSETTINGS_BANDWIDTH_HIGH TRUE
#define SETAUXBNCSETTINGS_BANDWIDTH_LOW FALSE
A TRUE in the Impedance variable opens the switches across J902 and J903, selecting high input
impedance. A FALSE selects 100 kΩ input impedance.
A TRUE in the Bandwidth variable opens the switch across J901, selecting high bandwidth. A FALSE selects
a low pass filter at nominally 20 Hz.
12 - 3
Appendix E – CE Certificate--Declaration of Conformity
Appendix E – CE Certificate
Redefining
Redefining Electrochemical Measurement
Declaration of Conformity
According to ISO/IEC Guide 22 and CEN/CENELEC EN 45014
Manufacturer's Name and Location:
Gamry Instruments
734 Louis Drive
Warminster, PA 18974
USA
This declaration is for the Gamry Instruments product models: Reference 600
Potentiostat/Galvanostat/ZRA.
The declaration is based upon compliance with the following directives:
EMC Directive 89/336/EEC as amended by 92/31/EEC and 93/68/EEC
Low Voltage Safety Directive 73/23/EEC as amended by 93/68/EEC
The declaration is based upon product compliance with the following standards as defined in report
number R0295-000 from Ergonomics, Inc. for safety analysis and report number RSI-2772L from
Radiation Sciences, Inc. for EMC test and analysis.
EMC Standards
EN 61000-4-2
EN 61326:2002-2
Title
EMC – Electrostatic discharge, Immunity
EMC – Radiated Emissions
Low Voltage Directive
Safety Standards
EN 61010-1:2001
EN 61010-2-081: 6/2003
Class/ Criteria
B
A
Title
Safety requirements for electrical equipment for measurement, control and laboratory
use, Part 1: General requirements.
Safety requirements for electrical equipment for measurement, control and laboratory
use, Part 2 Particular requirements for automatic and semiautomatic laboratory
equipment for analysis and other purposes
__
__
September 29, 2005_
Date
Signature
Dr. Gregory A. Martinchek, PhD
Title: President
Formal signed declaration is on file at Gamry, Inc.
13 - 1
Appendix E – CE Certificate--Certificate of Conformance
Certificate of Conformance
13 - 2
Comprehensive Index--
EIS speed, 8-7
electrical noise, 8-6
electrical transients, 1-5
electrons per second, 8-1
enclosed space, 1-3
environmental limits, 1-4
environmental stress, 1-3
External Signal, 6-6
Comprehensive Index
25 pin D, 4-9
AC adapter, 1-1
ADC channels, 3-5
air-cooling, 1-3
alligator clip, 5-2
ancillary apparatus, 8-8
application package, 4-13
Aux A/D, 12-1
Aux In BNC, 6-7
auxiliary electrode, 5-1
fans, 1-3
Faraday shield, 5-2, 8-5
filters, 3-5
firmware download, 6-2
floating ground, 5-1
Floating Ground, 6-3
floating ground binding post, 1-2
floating operation, 8-8
fluorescent lights, 8-6
black banana, 5-1
blue cell lead, 5-1
calibration, 4-13
calibration data, 3-7
capacitive cells, 7-1
CE Compliance, 1-5
cell cable, 5-1
replacements and specials, 5-2
ZRA connections, 5-2
cell connector, 4-9
Cell Connector, 6-1, 10-1
cell construction materials, 8-7
Cell LED, 6-2
Chassis Ground, 6-3
cleaning, 1-4
computer, 2-2
computer requirements, 4-2
computers - noise, 8-6
contract engineering, i
Control Overload, 6-2
conventions
notational, 2-2
counter electrode, 5-1
Counter Electrode, 10-1
Counter Sense, 10-1
Gamry Framework, 2-1
green cell lead, 5-1
ground, 10-1
Help system, 2-1
high frequency shunt, 7-3
high speed USB, 6-4
hints – cell design, 8-5
I Monitor BNC, 6-5
I Overload, 6-2
I/O connector, 6-5
input capacitance, 8-1
input current, 8-1
input impedance, 8-1
input leakage current, 8-4
inspection, 1-1
installation, 4-1
Johnson noise, 8-2
lead capacitance, 8-6
lead placement, 8-6
low I range dc calibration, 4-14
Luggin capillaries, 8-7
Luggin capillary, 7-2
data storage, 3-7
DC voltage, 3-8
DDS, 3-4
double insulation, 1-1, 4-2
materials, 8-7
measurement system model, 8-1
membrane cell connections, 5-3
Misc I/O connector, 6-5
Misc I/O Connector, 11-1
miscellaneous I/O connector, 11-1
E Monitor BNC, 6-6
E Overload, 6-2
earth ground, 1-2, 8-5, 8-8
EasyUSB, 3-7
14 - 1
Comprehensive Index--
motors, 8-6
Multiple Potentiostat Systems, 4-9
telephone assistance, i
temperature, 1-3
thermocouple, 6-4
noise, 8-4
operation, 1-4
orange lead, 5-1
oscillation, 7-1
Overload LED, 6-2
Universal Dummy Cell, 4-13
USB cable, 4-5
USB firmware, 3-7
USB LED, 4-6, 6-1
USB port, 6-4
Plug & Play, 4-3
power brick, 1-1
Power Connection, 4-4
Power Cord, 4-4
Power In, 6-3
power LED, 4-5
Power LED, 6-1
power line transient, 1-5
Power PC, 3-7
Power PC firmware, 3-7
Power switch, 4-5
Power Switch, 6-3
power-up self-test, 4-5
Problems, i
ventilation, 1-3, 4-2
Visual Inspection, 4-2
voltage noise, 8-4
Warranty, ii
WE Shield, 10-1
white cell lead, 5-1
Windows Update, 4-7
working electrode, 5-1
Working Electrode, 10-1
Working Sense, 10-1
WS Shield, 10-1
ZRA
cell connections, 5-2
radio frequency, 1-4
radio transmitters, 8-6
red cell lead, 5-1
Reference 600 – manual overview, 2-1
reference electrode, 5-1
Reference Electrode, 10-1
reference electrode impedance, 8-7
reference electrodes, 8-7
Refernce 600 - about, 2-1
RFI, 1-4
ringing, 7-1
safety, 1-1
schematic, 3-1
service, 1-4
service contract, i
shielding against noise, 1-2
shipping, 1-4
Sign Gen Out, 6-6
small signals, 8-1
software calibration, 9-1
specifications, 9-1
stability, 7-1
state-machine, 3-5
static electricity, 1-5
storage, 1-4
support, i
14 - 2
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