Fixed Frequency Impedance Course vs. Potential, Current, Time

Fixed Frequency Impedance Course vs. Potential, Current, Time
Fixed Frequency Impedance Course
vs. Potential, Current, Time, Temperature, …
© Zahner 08/2013
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C/E
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Introduction _________________________________ 4
1. C/E Main Page _____________________________ 6
1.1 File Operations ..............................................................................6
1.1.1 Open .......................................................................................................... 6
1.1.2 Save ........................................................................................................... 7
1.2 Display Impedance vs. Parameter ...............................................7
1.3 Scan Mode .....................................................................................8
1.3.1 Linear Scan ............................................................................................... 8
1.3.1.1 Linear Scan over Time ................................................................................................. 8
1.3.1.2 Linear Scan over Potential/Current ............................................................................ 9
1.3.1.3 Linear Scans Controlled by Analogue I/O-Channels ................................................ 9
1.3.2 Setpoint List.............................................................................................. 9
1.4 Scan Variable or Device..............................................................10
1.4.1 Internal Signals....................................................................................... 10
1.4.2 External Signals ..................................................................................... 10
2. Control Potentiostat _______________________ 12
3. Start Recording ___________________________ 13
4. Display Diagram __________________________ 14
4.1 Save Measurement......................................................................15
4.2 Create Data List ...........................................................................16
4.3 Export Drawing............................................................................17
4.4 Hardcopy......................................................................................17
4.5 Import Data List ...........................................................................17
4.6 Select Diagram ............................................................................18
4.7 Enter Crosshair Mode .................................................................18
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Introduction
The frequency response curve of the impedance of a physical object may always be described by a
set of impedance elements being interconnected in a characteristic way by parallel and serial links.
Rising pretensions to the concurrence between model and transfer functions increases the number of
impedance elements being needed. The model becomes more complicated.
C/E Recording
Often only several selected impedance elements of a model are scientifically relevant, e.g. the
components of an impedance describing the electrolytical conductivity or the double layer
capacitance. In this case the response curve of selected parameters may be found by an analysis of a
series of frequency response curves.
Recording the capacitance as a function of the potential may be done by measuring complete
impedance spectra being fitted with the same model. The numerical value of the relevant impedance
element (e.g. the double layer capacitance) may then be plotted as a function of the ordinal parameter
(e.g. the potential). This way is named as way “A”.
Under certain circumstances it is possible to find the parameter by measuring the impedance at a
constant frequency instead of recording complete impedance spectra. This may be done in a
frequency range where the real part or the imaginary part of the impedance is dominated by the
investigated parameter within a given measuring accuracy. C/E curves are now recorded by
measuring the impedance at varying potential and calculating the capacity either from the impedance
or from the admittance. This way is named “B”. Model “B” is fixed on either a parallel or a serial link of
one resistor and one capacitor.
In comparison to way “B” way “A” may always be gone but takes a lot more time. In a third way “C”
complete impedance spectra are needed as in way “A”. “C” takes the same measuring time like “A”
but saves time as fitting of a spectra series is not necessary. Instead of fitting the impedance is found
by cutting the impedance at a certain frequency and calculating the capacity like in way “B”. In
contrary to “B” way “C” allows to check the significance of the found numerical value by additional cuts
at other frequencies.
“A” and “C” result in files of data doublets of impedance and an additional parameter. Data coming
from “A” and “C” or directly from “B” contain the potential as second parameter. To analyse a series of
single spectra the program “SIM” offers the possibility to edit the second parameter and put in other
quantities as ordinal parameter.
C/E files are the base of further reports supported by the program C/E, e.g. several different graphical
representations. To analyse potential parameter curves to a chosen capacity (being put in either as an
absolute capacity in F or as a relative capacity in %) the potential will be calculated via the C/E curve
and forms a data doublet with the corresponding parameter. The generated potential parameter
curves are subject of putting in the reference capacity the corresponding parameter (e.g. temperature,
pH-value, concentration) may be put in, if not done while recording C/E curves via way “C”.
Further information
C/E files as well as potential parameter files will be automatically smoothed while being loaded from a
storage device. Manual smoothing is supported by functions in the different display subroutines. In
addition to smoothing C/E allows to spline a curve. Smoothing is a equivalent to a filter with a limited
bandwidth and makes sense in the case of spikes or noise being superimposed on a curve. By
smoothing a data reduction will take place and the smoothed curve will not exactly fit to the measured
points. Getting interpolated points in addition to the measured ones is an useful effect of smoothing
but makes only sense if there is a minimum number of 15 to 20 points.
In contrast to smoothing there is no data reduction when splining. Splining will be used to get
interpolations if there is only a small number of measured points. Splining is possible at a minimum
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number of three measured points and exactly fits to these points. The default setting of smoothing
operations is splining.
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1. C/E Main Page
Click on the
icons on the Main Menu page to open the C/E main page.
select diagram type
display resident C/E data as graphics
load/save C/E
data files
select scan mode
set U and I
parameters
scanning variable
or device
start recording
1.1 File Operations
1.1.1 Open
This function allows you to load/save C/E data from/to the hard disk
of your PC. Click on the icon and decide in the sub-menu, whether
you want to open previously stored C/E data or save actual C/E
data.
If there are no data in memory, this sub-menu is skipped.
After your decide to Open, a file browser will open displaying only
C/E data files (file extension .isp).
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Select a path and a file and click on the LOAD button to load the file
to the Thales software. Click on the Display Spectrum icon on the
C/E main page to display the data in a graphical form.
The next box shows the measurement parameters of the loaded
data. Click on it if you want to close it.
NOTE: Opening a file will switch off the potentiostat and
configures the potentiostat according to the loaded
measurement-settings automatically. Loading a measurement
file is an easy way to perform a new measurement with
previously used settings.
1.1.2 Save
If there are data in memory, usually after an EIS spectrum
measurement, you may want for Save them on hard disk for
storage.
A description box opens where you may input your measurement
parameters and comments. Some lines will be filled automatically
by the software (e.g. potential, current and measuring time) others
are free for the user to fill and are not used for any calculation.
button in the upper right
Accept the inputs by clicking on the
button. Click on the
corner or reject the inputs by clicking on the
button to call the calculator.
In the following browser navigate to the desired path,
Input a file name and
Click on the
button to save the data.
Click on the
button to cancel the saving.
1.2 Display Impedance vs. Parameter
Click on this icon to display the diagram resident in memory. This may be
measured or loaded data. The functions available in the display diagram
page are described later in this chapter.
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Click on this icon if you want to change the type of the diagram.
Select the type of the diagram type to be displayed here.
|Z|, Φ
Impedance modulus value
Phase angle between AC voltage and AC current
Ω
°
Z’, Z’’
Real part of the impedance
Imaginary part of the impedance
Ω
Ω
Y’, Y’’
Real part of the admittance
Imaginary part of the admittance
Ω-1
Ω-1
Complex
Modulo
complex modulo
Complex ε complex dielectric constant
parallel
Resistor
mathematical calculated curve
Ω
Resistor
serial
mathematical calculated curve
Ω
parallel
Capacity
mathematical calculated curve
F
Capacity
serial
mathematical calculated curve
F
parallel
M.-S.
mathematical calculated curve
F-2
M.-S.
serial
mathematical calculated curve
F-2
1.3 Scan Mode
1.3.1 Linear Scan
In Linear Scan Mode you scan through a range of the defined
quantity in equidistant steps (linear).
Start value
End value
Step width
Delay / s
: Value where the scan has to start
: Value where the scan is finished
: Interval in which the measurements have to be
carried out
: Delay between reaching a scan-point and
starting the measurement (settling time)
1.3.1.1 Linear Scan over Time
start time
Absolute time of the computer clock. The start time is set in units of hours,
minutes and seconds. During definition of the time parameters the actual time is
displayed in the input box.
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duration
Starting at the start time the program will start impedance measurements until
the total measurement time of duration has expired. The duration is set in units
of hours, minutes and seconds.
delay
Delay time defines the time difference of the starting times of two successive
impedance measurements.
!
Set the delay time higher than the estimated measurement time shown on the
Recording Parameters page. If measurements take longer than the delay time the
equidistance of the spectra can not be guaranteed or less spectra will be measured.
1.3.1.2 Linear Scan over Potential/Current
start value
Sets the potential or current at which the series measurement has to start.
Potential and current will be given in units of V and A, respectively.
end value
Destination potential or current at which the series measurement is stopped.
step width
Step width of potential or current between two successive measurements.
Setting the start value higher than the end value will require the input of a
negative step width.
delay
After the new value of potential or current is reached the program waits for this
number of seconds to ensure steady state conditions at the object.
!
The delay time should not been defined too short because changes in potential and
current may cause distortions of equilibrium. Allow the system to settle before
continuing with measurements.
The effect of the series control by DC-set-voltage or DC-set-current is related to the
actual working mode of the potentiostat:
Use DC-voltage only in potentiostatic mode.
Use DC-current only in galvanostatic- or pseudo-galvanostatic mode.
1.3.1.3 Linear Scans Controlled by Analogue I/O-Channels
Linear scans using additional analogue i/o-channels are working in a similar way as linear scans over
potential or current do. The range parameters and the step width are given in the physical units
defined for the corresponding channel on the Data Acquisition Setup page. The physical unit set
there is displayed at the top of the appearing input box.
start value
Sets the value at which the series measurement has to start. Potential and current
will be given in units of V and A, respectively.
end value
Destination value at which the series measurement is stopped.
step width
Step width between two successive measurements. Setting the start value higher
than the end value will require the input of a negative step width.
delay
After the new value is reached the program waits for this number of seconds to
ensure steady state conditions at the object.
!
The delay time should be defined sufficiently high to offer the system some time to
get settled.
1.3.2 Setpoint List
Setpoint List mode lets you define a list of points at which the system
has to measure. The list has not to be linear or steady.
In the first input box you define a delay time valid between the individual
impedance measurements for settling. After reaching a set point, the
software waits for the duration of the delay time before the
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software waits for the duration of the delay time before the
measurement is started.
In the second box you may input the set points in the quality of the scan
parameter set in the Variable Parameters box.
Up to 99 set points can be defined but only 12 points are displayed in
the box. You can scroll through the list using the cursor keys or the
RETURN key of your keyboard. The transition between two points
always is a linear ramp.
1.4 Scan Variable or Device
In this section you set the parameters of the scan variable. This may be an internal signal (time,
potential, current) or an external signal (analog input, analog output, interface control channel). For
using external signals you may need an optional hardware such as TEMP/U, FE42, DA4, etc.
1.4.1 Internal Signals
Impedance will be recorded at a fixed frequency over a certain interval of
time, allowing studies of time dependent processes.
Impedance will be recorded at a fixed frequency in dependence of the DC
potential, allowing studies of potential dependent processes.
Impedance will be recorded at a fixed frequency in dependence of the DC
current, allowing studies of processes dependent on the current density.
1.4.2 External Signals
Four analogue outputs are provided by an optional DA4 DA-converter
module. The channels can be calibrated and correlated to any quantity to be
controlled in the Signal Acquisition Setup page:
Additional analogue input channels are provided by the optional modules
FE42 and TEMP/U. In the Signal Acquisition Setup page the inputs can be
calibrated and linked to one of the 'digital instrument displays' of the Signal
Acquisition & Output Control page:
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Generally, Thales is able to communicate via TCP/IP with external
measurement and control units (NET-VIs) connected to any computer in the
network. Besides this, an Eurotherm 2404CG, which is able to control the
temperature of an oven, may be connected directly to the COM port of the PC
controlling the IM instrument. This opens a cheap way to perform series
measurements over controlled temperature.
C/E
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2. Control Potentiostat
The Control Potentiostat page is very useful for testing your external measurement setup,
such as cabling, cell, electrodes, connections to the object, etc. Here you may apply different
combinations of AC and DC voltages and currents at frequencies of interest. You may have a (first)
look at the measurement values and signals at the selected frequency. Furthermore, the AC- and DCparameters DC voltage/current, AC amplitude and potentiostat mode (potentiostatic or galvanostatic)
are to be defined here for an C/E measurement to follow. And – very important – the potentiostat is
switched on and off here. Please note, that the potentiostat is switched off automatically, when the
potentiostat mode is changed.
Also the final condition of the potentiostat can be selected here. If a C/E measurement is started with
the potentiostat switched on, the potentiostat will remain operational after the C/E measurement has
been completed. If the potentiostat has been switched off before starting a C/E measurement it will be
switched off at the end of the measurement.
POT switch
set POT mode
select POT device
close button
set DC voltage
or DC current
global measuring
settings
DC voltage
display
go to
page
Calibration
DC current
display
set AC display type
set frequency
go to Check Cell
Connections
set AC amplitude
AC voltage display
set average
count
voltage spectrum
AC current display
current spectrum
AC display 1
AC display 2
The potentiostat can be set to the C/E starting potential and switched on manually, what will avoid the
automatic insertion of a start ramp between the actual potential and the C/E starting potential. The
ramp speed may be altered in the general measurement setup under the point “DC-more”.
C/E
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3. Start Recording
After all parameters have been set properly, a new measurement can be started by
activating the button <GO>. If a new measurement is started, the program will prompt the recording
window shown below.
realtime displays
time domain
frequency domain
voltage
current
voltage
current
numerical displays:
realtime
data display
ramp to next
potential step
and delay time
impedance modulus
phase angle
frequency
DC voltage
DC current
break button
The measured impedance data is plotted online in the data window. At the top of the recording window
four realtime displays shows the voltage and current signals in time and frequency domain. Five
'digital' instruments on the right side indicate the numeric values of the actually measured data. A
running measurement can be terminated by using the <ESCAPE> function or by pressing the stopbutton.
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4. Display Diagram
The 'display diagram' function will be entered automatically after completion of a C/E
measurement, and it may be recalled from the C/E main page if a the measurement is present. That
C/E measurement will be displayed on the screen. Data can be exported to other programs by the
standard i/o functions.
The C/E curve measured (or loaded by file) last is displayed as shown above after the 'display
diagram' has been entered. The data window is situated in the middle of the screen. On the right, five
i/o standard interfaces offer transfer functions of this data.
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4.1 Save Measurement
Save the
recorded data + the measurement parameters + the comments to the
hard disk and return to the C/E page.
When clicking on either of the buttons a description box opens where
you may input your measurement parameters and comments. Some lines
will be filled automatically by the software (e.g. potential, current and
measuring time) others are free for the user to fill. User parameters are
not used by the software for any calculation. They are for the user’s
information only.
Accept the inputs by clicking on the
button in the upper right corner or
reject the inputs by clicking on the
button. Click on the
button to
call the calculator.
In the following browser navigate to the desired path,
input a file name and
button to save the data or
click on the
click on the
button to cancel the saving.
Note: It is recommended to use one of the save-functions in order to
store (and recall later) the ECW state corresponding with that
measurement.
C/E
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4.2 Create Data List
Creates an ASCII list of the data:
and copies it to the Windows® clipboard
or saves it as plain text-file
or copies it to ZEdit
Example of an ASCII list of a C/E measurement
File.........:
test_exp - SEP,01.2009
System.......:
Temperature..:
Time.........:
Freq./Samples:
Comment......:
ZENNIUM#42001
1KHz / n=1
09:34:12-09:39:46
Testbox EXP
-4V...4V
100mV step
Impedance vs parameter
Lines:
81
Columns: 5
Number
1
2
3
4
5
6
7
8
9
10
...
...
...
76
77
78
79
80
81
Potential
-4.000e+00
-3.900e+00
-3.800e+00
-3.700e+00
-3.600e+00
-3.500e+00
-3.400e+00
-3.300e+00
-3.200e+00
-3.100e+00
...
...
...
3.500e+00
3.600e+00
3.700e+00
3.800e+00
3.900e+00
4.000e+00
Impedance/Ohm
2.118e+01
2.106e+01
2.090e+01
2.074e+01
2.058e+01
2.042e+01
2.026e+01
2.010e+01
1.994e+01
1.978e+01
...
...
...
1.927e+01
1.946e+01
1.967e+01
1.985e+01
2.005e+01
2.027e+01
Phase/deg
-52.6
-52.4
-52.0
-51.7
-51.4
-51.1
-50.7
-50.4
-50.0
-49.6
...
...
...
-48.4
-48.8
-49.3
-49.7
-50.2
-50.7
Signific.
0.998
0.999
0.999
0.999
0.999
0.999
0.999
0.999
0.999
0.999
...
...
...
0.999
0.999
0.999
0.999
0.999
0.999
Time/s
0.0
5.5
10.2
15.0
19.8
25.3
30.1
34.8
39.6
44.4
...
...
...
306.5
311.3
317.0
321.8
326.5
331.31
Note: Unlike to the save-functions the ECW state corresponding with the measurement is not
content of the export data.
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4.3 Export Drawing
Passes the actual graph as high quality vector
graphic to the Windows clipboard
saves the graph as an EMF graphic file
Transfers the graph to the CAD graphic
editor section of Thales.
Edit the graph manually in the CAD section of
Thales for later clipboard or EMF export.
4.4 Hardcopy
Create a bitmap copy of the screen for export or printing:
Perform the selected output operation
Do a form feed
Select the output properties:
landscape = big format (DIN-A4) to printer
upright = small format (DIN-A5) to printer
to clipboard = sends screen to the Windows clipboard
save as file = saves the screen content as a bitmap file
4.5 Import Data List
- inactive within C/E -
C/E
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4.6 Select Diagram
Select the type of the diagram type to be displayed here.
|Z|, Φ
Impedance modulus value
Ω
Phase angle between AC voltage and AC current °
Z’, Z’’
Real part of the impedance
Imaginary part of the impedance
Ω
Ω
Y’, Y’’
Real part of the admittance
Imaginary part of the admittance
Ω-1
Ω-1
Complex
complex modulo
Modulo
Complex
complex dielectric constant
ε
parallel
mathematical calculated curve
Resistor
Ω
Resistor
mathematical calculated curve
serial
Ω
parallel
mathematical calculated curve
Capacity
F
Capacity
mathematical calculated curve
serial
F
parallel
M.-S.
mathematical calculated curve
F-2
M.-S.
serial
mathematical calculated curve
F-2
4.7 Enter Crosshair Mode
Move cursors through the curves with the
mouse. The course leads through the history
of the data source: moving from left to right
means moving from the first samples
recorded to later ones.
Use the cursor-left/right keys for fine steps.
You leave the crosshair mode by clicking the
middle mouse key or the <ESCAPE> button.
If more than one data set is displayed, use
the cursor-up/down keys to change from one
curve to the next.
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