LI-610 Manual - LI
LI-610
Portable Dew Point Generator
Instruction
Manual
®
LI-610
Portable Dew Point Generator
Operating and
Service Manual
NOTICE
The information contained in this document is subject to change without notice.
LI-COR MAKES NO WARRANTY OF ANY KIND WITH REGARD TO THIS MATERIAL, INCLUDING, BUT
NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE. LI-COR shall not be liable for errors contained herein or for incidental or consequential
damages in connection with the furnishing, performance, or use of this material.
This document contains proprietary information which is protected by copyright. All rights are reserved. No part of
this document may be photocopied, reproduced, or translated to another language without prior written consent of
LI-COR, Inc.
© Copyright 1991, LI-COR, Inc.
Printing History
New editions of this manual will incorporate all material since the previous editions. Update packages may be used
between editions which contain replacement and additional pages to be merged into the manual by the user.
The manual printing date indicates its current edition. The printing date changes when a new edition is printed. (Minor
corrections and updates which are incorporated at reprint do not cause the date to change).
1st Printing - August, 1991
2nd Printing - November, 2004
Publication Number 984-06659
August, 1991
LI-COR, Inc. • 4421 Superior Street • Lincoln, Nebraska 68504 • 402-467-3576
FAX: 402-467-2819
Toll-free 1-800-447-3576 (U.S. & Canada)
E-mail: envsales@licor.com
www.licor.com
ii
TABLE OF CONTENTS
Section I. UNPACKING AND INITIAL INSPECTION
What's What ..................................................................................................................................................
Optional Accessories ....................................................................................................................................
1-1
1-2
Section II. PRE-OPERATION
Setup ..............................................................................................................................................................
Filling the Radiator ...............................................................................................................................
Filling the Condenser Block .................................................................................................................
Power On.......................................................................................................................................................
2-1
2-1
2-3
2-4
Section III. OPERATION
General Description ......................................................................................................................................
Air Flow Through the LI-610...............................................................................................................
Water Flow In the LI-610 .....................................................................................................................
Operation .......................................................................................................................................................
Command Input ............................................................................................................................................
Analog Output...............................................................................................................................................
Theory of Operation .....................................................................................................................................
Ideal Gas Laws ......................................................................................................................................
Pure Water Vapor..................................................................................................................................
Moist Air................................................................................................................................................
Pressure Effects .....................................................................................................................................
Temperature Effects ..............................................................................................................................
Relative Humidity .................................................................................................................................
Sample Calculations..............................................................................................................................
Additional Relationships.......................................................................................................................
3-1
3-1
3-2
3-3
3-4
3-4
3-5
3-5
3-6
3-7
3-8
3-10
3-10
3-11
3-13
iii
Water Sorption ......................................................................................................................................
Maximum Flow Rates...........................................................................................................................
References .....................................................................................................................................................
3-13
3-13
3-16
Section IV. CALIBRATING LI-COR INSTRUMENTS
General Information .....................................................................................................................................
Calibrating the LI-6400 H2O Analyzer .......................................................................................................
Setting the H2O Span ............................................................................................................................
Calibrating the LI-7000 CO2/H2O Infrared Gas Analyzer ........................................................................
Preliminary ............................................................................................................................................
Calibration Instructions.........................................................................................................................
I. Reference (Cell A) is Known and Constant....................................................................................
II. Reference (Cell A) is Known, but not Constant............................................................................
III. Calibrating for REM Operations...................................................................................................
User Calibration Example.....................................................................................................................
Calibrating the LI-7500 CO2/H2O Infrared Gas Analyzer ........................................................................
Preliminary ............................................................................................................................................
Zero CO2 ................................................................................................................................................
Zero H2O ...............................................................................................................................................
Span CO2 ...............................................................................................................................................
Span H2O ...............................................................................................................................................
Calibrating the LI-840/A CO2/H2O Infrared Gas Analyzer ......................................................................
Calibrating the LI-COR LI-6262 CO2/H2O Infrared Gas Analyzer .........................................................
Preliminary ............................................................................................................................................
Absolute Mode H2O Zero Calibration.................................................................................................
Absolute Mode H2O Span Calibration ................................................................................................
Differential Mode H2O Zero Calibration ............................................................................................
Precautions.............................................................................................................................................
Calibrating the LI-COR LI-1600 Steady State Porometer RH Sensor......................................................
Initial Setup............................................................................................................................................
Calibration: Setting the Zero ................................................................................................................
Calibration: Setting the Span................................................................................................................
Check Intermediate Values...................................................................................................................
Calibrating the LI-COR LI-6200 or LI-6000 Portable Photosynthesis System RH Sensor ....................
Precalibration.........................................................................................................................................
Calibration: Setting the Zero ................................................................................................................
Calibration: Setting the Span................................................................................................................
Check Intermediate Values...................................................................................................................
iv
4-1
4-1
4-1
4-4
4-4
4-6
4-7
4-7
4-8
4-10
4-12
4-12
4-14
4-14
4-14
4-15
4-16
4-17
4-17
4-18
4-18
4-19
4-19
4-20
4-20
4-21
4-22
4-23
4-24
4-24
4-26
4-27
4-28
Calibrating Relative Humidity Sensors (General) ......................................................................................
Calibrating Dew Point Hygrometers (General) ..........................................................................................
References .....................................................................................................................................................
4-29
4-29
4-29
Section V. MAINTENANCE
Draining the LI-610 ......................................................................................................................................
Condenser Block ...................................................................................................................................
Radiator Assembly ................................................................................................................................
Internal Air Filter ..........................................................................................................................................
Internal Water Filter Screen .........................................................................................................................
External Fan Filter ........................................................................................................................................
Cleaning the Condenser Block.....................................................................................................................
Fuses ..............................................................................................................................................................
Replacing the Air Pump Diaphragm ...........................................................................................................
Recharging the 6200B Battery.....................................................................................................................
5-1
5-1
5-2
5-2
5-3
5-4
5-4
5-5
5-5
5-7
Section VI. TROUBLESHOOTING
Appendix A.
Appendix B.
Appendix C.
Appendix D.
Specifications
Saturation Vapor Pressure Table
Psychrometric Charts
LI-610 Calibration Traceability
Warranty
v
Section I.
Unpacking & Initial Inspection
What's What
Check the packing list included with your LI-610 to verify that you have
received everything that was ordered, and that you have also received the
following items:
Spare Parts Kit
This bag contains replacement parts for your LI-610. As you become
familiar with the Dew Point Generator you will learn which items to
keep close at hand, and which items can be stored away.
Squeeze Bottle
A 250 ml plastic squeeze bottle is included to aid in filling the radiator
assembly.
Syringe
A plastic syringe is included to facilitate filling and draining of the
condenser block in the LI-610. Refer to Sections 2 and 5, respectively,
for complete filling and draining instructions.
Algicide
A small bottle of liquid algicide is included, to prevent the formation of
algae in the radiator assembly of the LI-610. Refer to Section 2 for
complete instructions.
610-04 BNC millivolt
Leads
One set of millivolt leads terminated with a BNC connector is included
for connection to either the "Analog Output" or "Command Input"
fittings on the LI-610 front panel. See Section 3 for a complete
description of the function of these connectors.
610-01 AC Module
108-126/216-252 VAC, 48-66 Hz, for AC operation.
Unpacking & Initial Inspection
1-1
Section 1
Optional Accessories
Several optional accessories are available for use with the LI-610,
including:
610-02 Relative Humidity Calibration Accessories - for calibrating the
LI-6200 or LI-6000 Portable Photosynthesis System relative humidity
sensors, and the LI-1600 Steady State Porometer relative humidity sensor.
610-04 BNC mV Leads - for connecting to either the "Analog Output" or
"Command Input" fittings on the LI-610 front panel (one set included
with the LI-610). One set is included; a second set is required if you wish
to use the Analog Output and Command Input functions simultaneously.
6200B Rechargeable Battery (10.5 - 16 VDC). The 6200B Rechargeable Battery is tested and fully charged before it leaves the factory, but
may discharge during shipping. It is a good idea to test your battery to
make sure that it is charged. If the battery is below 12 volts, it should be
charged before use. Refer to Section 5 for charging instructions. The
6200B requires the LI-6020 Battery Charger for recharging.
Never store batteries in a discharged state.
every three months.
Charge stored batteries
LI-6020 Battery Charger (92-138/184-276 VAC, 47 to 63 Hz).
Battery Leads - for connection to a user-supplied battery (10.5-16VDC)
or other DC power supply.
1-2
Unpacking & Initial Inspection
Section II.
Pre-Operation
Setup
Two distinct systems must be filled with distilled (or deionized) water
before operating; the radiator assembly, located within the LI-610 case,
and the condenser block assembly, located externally.
Filling the Radiator
To fill the radiator assembly, remove the black radiator fill cap on the top
of the LI-610 instrument case (Figure 2-1). The cap is not threaded, and
can be pulled straight up.
• Use the plastic squeeze bottle included with the LI-610 to add distilled
or deionized water to the radiator reservoir, until the water level is
visible in the fill tube.
• Connect the LI-610 to your power source (AC or battery).
• Turn the power switch ON. Turn the COOLER switch ON momentarily to flow water through the water pump and radiator assemblies.
Shut the LI-610 off and continue to fill the reservoir in this manner
until the water level remains visible in the fill tube. The radiator
assembly requires approximately 200 ml of water to completely fill to
this level.
TO PREVENT PERSONAL INJURY, DISCONNECT THE LI-610
FROM AC POWER WHEN FILLING THE RADIATOR
ASSEMBLY.
At this time, add 15-20 drops (2 ml) of algicide (included with the
LI-610) to the radiator reservoir. Replace the radiator fill cap.
If you plan to store the LI-610 in freezing conditions, drain the radiator
and condenser block assemblies completely. To operate the LI-610 in
freezing conditions, fill the radiator assembly (not the condenser) with a
mixture of ethylene glycol (one formulation of which is commonly called
“antifreeze”). A 50/50 mixture of ethylene glycol/water will protect the
radiator from freezing to approximately -40 °C.
Pre-Operation
2-1
Section 2
Ethylene glycol is the recommended antifreeze; do not use propylene
glycol or other antifreeze mixtures.
Radiator
Fill
Figure 2-1. LI-610 top view, showing location of radiator fill cap.
2-2
Pre-Operation
Section 2
Filling the Condenser
Block
The gold-plated condenser block assembly requires approximately 20 to
25 ml of distilled water to function normally. Follow these steps when
filling the condenser block assembly:
• Remove the plastic capnut located at the front left corner of the
condenser block assembly (see Figure 2-2). The condenser block can
now be filled using the 30 ml syringe included in your spare parts kit.
• Thread a female Luer lock (included in the spare parts kit) into the
syringe, and draw 20-25 ml of water into the syringe. Attach a male
Luer lock to the fill/drain port on the LI-610. Connect the two Luer
locks with a short section of 1/8” ID Bev-a-line tubing, as shown at left.
30cc
25
Syringe
20
15
10
5
Female
Luer
Lock
Fill/drain
port
Bev-a-line
Tubing
Condenser
block
Male
Luer
Lock
Figure 2-2. Location of the condenser block fill/drain port.
• Slowly add water to the condenser block; if the block is properly filled
the water level in the fill/drain tube will read midway between the
“Max” and “Min” marks on the condenser block ruler. Fill or drain to
Pre-Operation
2-3
Section 2
this level, as needed. If the condenser block is overfilled, simply use
the syringe to draw some water out of the fill/drain tube.
• Fill the syringe with air after filling the condenser block with water,
and syringe the air into the fill tube to remove any water which may
adhere to the side of the tube. This adhesion can cause a false water
level reading in the fill tube if it is not purged. Check the water level
reading in the fill/drain tube, and repeat, if necessary.
• After filling to the proper level, replace the threaded capnut.
It is recommended that the distilled water in the condenser block
assembly be changed every 2 days with continuous use.
The water level in the condenser should be monitored closely, particularly
if the temperature and water vapor content of the input air stream is
significantly different than the LI-610 set dew point. In this case, water
vapor will either condense out of the input air stream, thereby raising the
water level in the condenser, or evaporate out of the condenser into the
output air stream, lowering the condenser water level.
The condenser water may need to be changed more frequently if the
input air stream contains CO2 at levels higher than 500 ppm. LI-COR
has found that high CO2 levels cause the formation of precipitates within
the condenser block, which can cause the water to foam, leading to
unstable flow rates. If the rotameter gauge(s) fluctuates erratically, it
may be an indication that the condenser water needs to be changed.
Power On
2-4
Pre-Operation
1.
The 6200B Rechargeable Battery and the 610-01 AC Module both fit
into the compartment on the back of the LI-610. Loosen the two
thumbnuts, and lift the right side of the retaining strap to access the
compartment. Place the 6200B in the compartment, and replace the
retaining strap. See Table 2-1 for the approximate battery life of the
6000B and 6200B batteries when used with the LI-610.
2.
If you are installing the 610-01, remove the retaining strap. Install
the AC Module and replace the retaining strap. Tighten the thumb-
Section 2
nuts securely. Connect the power cord to one of the connectors
labeled 10.5-16 VDC on the rear panel.
Table 2-1. Hours of Battery Life for 6000B and 6200B Batteries
(@ 25 °C ambient).
Hours of Battery Life (approximate)
Set Dew Point
20 °C
6000B
6200B
2.5-2.75
5.0-5.5
10 °C
0 °C
2.0-2.25
1.50-1.75
4.0-4.5
3.0-3.5
When the battery voltage reaches approximately 10.3 - 10.4 volts, the
LOW BATT light on the instrument front panel (Figure 2-3) will
illuminate, indicating that a system shutdown will occur if a charged
battery is not connected. Connect a fresh battery to continue
operation; the LOW BATT light will shut off. Instructions for
recharging the 6000B and 6200B batteries are given in Section 5.
The LI-610 will shut down when the battery voltage reaches
approximately 10 volts. The Peltier coolers, liquid pump, air pump,
fan, and display will turn off to conserve power. The LI-610 should
be turned OFF to prevent further battery discharge. Connect a fresh
battery, and if you haven't already done so, turn the LI-610 OFF and
back ON to reset the shutdown circuit. The LOW BATT light will
shut off, and normal operation will resume.
If AC line voltage is being used (with the 610-01 AC Module), make
sure the AC VOLTAGE selector on the AC module is set correctly
(choose the 115 setting for 108-126VAC, or the 220 setting for 216252 VAC), and plug the line cord into the AC receptacle.
WARNING!
To prevent personal injury, never operate the LI-610 AC module if it
is not installed in the Dew Point Generator.
3.
Turn the POWER switch on the front panel ON. The display will
show the temperature setpoint (TEMP SET), the actual temperature
(TEMP °C) of the condenser, or the battery voltage (BATTERY),
Pre-Operation
2-5
Section 2
depending upon the position of the function switch on the right side
of the display.
Turn the COOLER switch ON. The liquid pump will start circulating
water through the Peltier coolers and the radiator assembly. When
the AIR PUMP is switched ON and the FLOW ADJUST VALVE is
opened, the LI-610 will begin to generate an airstream with a dew
point temperature equal to the condenser temperature established
with the TEMP SET knobs.
Radiator
Fill Cap
Temperature
Set Knobs
ON/OFF Switch
Flow Adjust
Valve
Display
Analog Output
Low Battery LED
Rotameters
Temperature
Set Switch
Air Output
Ports
Command Input
Figure 2-3. LI-610 front panel.
2-6
Pre-Operation
Section III.
Operation
General Description
The LI-610 Portable Dew Point Generator is a completely self-contained
instrument that is used to generate a moist air stream with a known dew
point.
A source of dry or ambient air is bubbled through a condenser block
assembly containing a water bath, whose temperature is precisely
controlled by a series of Peltier thermoelectric coolers. The internal
radiator and fan assembly dissipates the heat generated by the coolers,
providing a self-contained cooling system.
Water and air flow through two distinct paths within the LI-610 to
produce a moist air stream with a known dew point.
Air Flow Through
the LI-610
Air is drawn into the LI-610 through the AIR IN fitting on the instrument
back panel. Any impurities are removed from this air stream by a filter
before it reaches the air pump. Air leaving the pump passes through a
flow adjust valve on the instrument front panel, where the rate of air flow
through the LI-610 is controlled (see Figure 3-1).
The air stream then enters the two copper condenser blocks via the TO
CONDENSER fitting, where a bubbler stone is used to maximize the airto-water surface area, which ensures that air leaving the condenser blocks
is completely saturated with water vapor. Water vapor leaving the
condenser blocks through the FROM CONDENSER fitting is split into
two separate air streams, which are supplied to OUTPUT 1 and OUTPUT
2 on the front of the instrument. The rate of flow through these outputs is
indicated by two rotameters on the front panel. Flow is divided between
the outputs using the flow control valve on output port #2.
Operation 3-1
Section 3
Air Inlet
Filter
Air Output
Port #2
Pump
Air Flow Path
Rotameter
Valve
Rotameter
Air Output
Port #1
Two-Stage
Condenser
Peltier Cooler
Cooling Water Path
Radiator
Pump
Reservoir
Figure 3-1. Path of air and water flow through the LI-610.
Water Flow In
the LI-610
An internal radiator assembly is used in the LI-610 to provide a means
of dissipating the heat generated by the two Peltier coolers attached to
the condenser block (Figure 3-1).
The Peltier coolers are thermoelectric devices which absorb or liberate
heat, depending upon the direction of electrical current flow through the
junction of dissimilar metals.
When the coolers are switched ON, current flows in a direction which
causes heat to be absorbed or generated, based on the position of the
TEMPERATURE SET controls on the front panel, thereby lowering or
raising the temperature of the water present in the block. The condenser
blocks are copper, which is an excellent conductor of thermal energy. A
continuous flow of water between the coolers and the radiator allows
excess heat to be dissipated.
A precision platinum ResistanceTemperature-Detector (RTD) is used to monitor the temperature of the
condenser block (the condenser temperature is limited to +50 °C).
3-2
Operation
Section 3
If the temperature on the hot side of a Peltier cooler exceeds +65 °C, the
coolers will automatically shut down to prevent overheating. The
coolers will subsequently turn back on when the temperature drops
below this threshold.
Operation
After filling the LI-610 with distilled water (Section 2), the instrument is
ready to begin generating a water vapor stream.
1.
Turn the POWER switch ON. The display shows the temperature
setpoint (TEMPERATURE SET), the actual condenser block temperature (TEMP °C), or the battery voltage (BATTERY), depending
upon the position of the function switch adjacent to the display.
2.
Set the function switch to the TEMP SET position. Use the COARSE
and FINE TEMP SET knobs to set the desired dew point temperature
of the output air stream. The COARSE adjustment knob changes the
temperature set by large increments, and allows you to get close to
the desired set point very quickly. The FINE temperature adjustment
knob is then used to set the dew point precisely.
3.
Set the function switch to the TEMP °C position, and turn the
COOLER switch ON. The Peltier coolers, liquid pump, and radiator
fan will turn on.
4.
Turn the AIR PUMP switch ON. The air pump will turn on, starting
the flow of moist air out of OUTPUT 1 and OUTPUT 2. Use the
FLOW ADJUST knob to control the rate of air flow through the
LI-610. If you wish to shut off OUTPUT 2, simply turn the knob on
the rotameter above OUTPUT 2 clockwise until the flow is shut off,
and the rotameter shows zero flow.
Allow the LI-610 time to reach the desired dew point. The time required
will depend on the difference between the desired dew point
temperature, and the temperature of the cooling water used to remove
heat dissipated by the Peltier coolers. As an example, at 20 °C ambient
air temperature, the LI-610 will take approximately 10 minutes to reach a
dew point of 0 °C, assuming that the cooling water temperature is also at
or just above 20 °C.
Operation 3-3
Section 3
Command Input
The Command Input connector is used to provide a means of controlling
the temperature setting of the LI-610 from an external device (i.e., a
computer with an analog output board). One BNC connector with
attached millivolt leads is included for connection to this device.
The Command Input requires a 0 to 5 volt input; the corresponding
temperature set is linear, and is equivalent to 1 °C per 100 mV. For
example, an input signal of 3250 mV would produce a dew point
temperature output of 32.50 °C. The display will show the actual
temperature set point for the Command Input when the selector switch is
in the “Temp Set” position, regardless of what the knob setting is.
Connect the red lead from the BNC connector to the positive terminal of
the output device, and the black lead to the signal ground. The output
device must be able to supply 1 mA drive current. A source impedance
10 is required for an error 0.1%.
NOTE: The LI-COR LI-6400/XT Portable Photosynthesis System can be
configured to provide an analog output channel that controls the dew
point temperature of the LI-610. If both instruments are powered by AC
power, a "ground loop" can develop, in which there is more than one
ground connection path between the two pieces of equipment. Ground
loop-induced voltages cause unwanted signal noise that can affect the
operation of the LI-610. If you are using the LI-6400/XT and LI-610 in
this manner, we recommend that you isolate the two circuits by operating
one or both of the instruments with battery power.
Analog Output
The Analog Output connector is similar to the Command Input
connector, in that BNC millivolt leads are used to provide an analog
signal from the LI-610 to an external recording device. Analog output is
also linear (± 5 volts), and is equivalent to 1 °C per 100 mV.
Connect the red lead to the positive terminal of the readout device, and
the black lead to the signal ground. The readout device should have an
input impedance 100k for an error 0.1% (the Analog Output
impedance is 100).
3-4
Operation
Section 3
Theory of Operation
Ideal Gas Laws
When a gas stream passes through the LI-610 condenser, water vapor is
added or removed so that the exiting gas stream is saturated at the
condenser temperature. In most cases, that gas stream will be air, so we
shall consider a description of moist air.
Atmospheric gases at pressures near ambient conform closely to the ideal
gas law. The partial pressure of an ideal gas is given by
piV = niRT,
3-1
where pi is the partial pressure of gas component i {kPa}, V is volume
{m3}, ni is the number of moles of gas component i, R is the universal gas
constant {0.008314 m3 kPa mol-1 K-1}, and T is absolute temperature
{°K}. Dalton's Law of partial pressures states that the total pressure, P,
of an ideal gas mixture equals the sum of the component partial pressures.
For moist air,
P = p N 2 + p O 2 + ... + e
or,
P = pi + e
3-2
where pi is the sum of partial pressures of dry air components, also
expressed as Pa, and e is the partial pressure of water vapor. Therefore,
P = Pa + e.
The partial pressure of water vapor may also be expressed as a mole
fraction. The mole fraction, X, of a component j in a mixture or solution
is defined as, Xj = nj/ni. Combining equations (1) and (2) with the
definition of mole fraction, it can be shown that for an ideal gas mixture,
Xj = pj/P. Specifically, let w be the mole fraction for water vapor {mmol
mol-1}, then
w = 1000
e
P
3-3
Operation 3-5
Section 3
Pure Water Vapor
The amount of water that can remain in the gaseous state at equilibrium
is limited. When pure water vapor is in stable equilibrium with a plane
surface of pure water or ice, with constant temperature and pressure at
the interface, it is said to be saturated. The partial pressure of pure water
vapor at saturation is a function of temperature alone, and is called the
saturation vapor pressure. Tabulated values of the saturation vapor
pressure of pure water vapor as a function of temperature based upon the
formulation of Goff and Gratch (1946) are given in the Smithsonian
Meteorological Tables (List, 1984).
Equations relating saturation vapor pressure to temperature based upon
those data are given by Lowe (1976) and LI-COR (1990). Lowe's
equation is a 6th order polynomial that gives accurate results (Table 3-1,
equation 3-11) and can be rapidly calculated on a digital computer.
However, it has the major disadvantage that it is easily applied in only
one direction, i.e., to compute vapor pressure from temperature. Given a
vapor pressure, it is difficult to solve Lowe’s equation for temperature.
Lowe's equation is used in the LI-6252 CO2 Analyzer to compute vapor
pressure from a dew point provided by an external dew point hygrometer.
Equation 5-12 (LI-6262 CO2/H2O Analyzer Instruction Manual) of
LI-COR (1990) can be converted to the form: saturation vapor pressure at
This equation (Table 3-1,
temperature T, e(T) = a 10[bT/(c+T)].
equation 3-12) gives good accuracy from -50 °C to +50 °C, and can be
solved for either saturation vapor pressure, e(T) or temperature, T. It is
used in the LI-6262 to compute the dew point temperature from vapor
pressure.
3-6
Operation
Section 3
Moist Air
The saturation vapor pressure of water vapor in air is slightly different
from that of pure water vapor. It is a function of temperature as well as a
weak function of total pressure. Buck (1981) presents several equations
with varying degrees of complexity and accuracy that are fit to recent
data relating saturation vapor pressure of moist air over water and ice to
temperature and pressure (Wexler, 1976, 1977; Hyland, 1975).
Generally, these equations have the form
e(T,P) = a f(T,P) eg(T).
The pressure dependence is described by a multiplier called the
enhancement factor, f(T,P). The enhancement factor is defined as the
ratio of the vapor pressure of moist air to that of pure water vapor (Buck,
1981), both at the same temperature. It is primarily a function of
pressure, but the most detailed formulations also include a weak
temperature dependence (Buck, 1981). Adequate accuracy results if the
enhancement factor is given a constant value of 1.004 (Table 3-1) for
barometric pressures above 80 kPa and temperatures from 0 °C to 50 °C.
A more accurate formulation is given in equation 3-5 and Table 3-1,
although it is evident from Table 3-1 that this is hardly necessary in
practical calculations. Therefore, we shall consider e(T,P) = e(T) for
pressures above 80 kPa.
The recommended equation for routine calculations of moist air
saturation vapor pressure, e(T), at a given temperature {°C}, and total
pressure above 80 kPa is
17.502T
e(T) = (0.61121)(1.004)e 240.97 + T
or,
3-4
17.502T
e(T) = 0.61365e 240.97 + T {kPa}
The dew point is the temperature at which moist air will be saturated with
water vapor if it is cooled at constant pressure and mole fraction. The
LI-610 generates an air stream that is saturated at the temperature of the
condenser block, hence the name Dew Point Generator.
Operation 3-7
Section 3
Pressure Effects
When the air stream leaves the LI-610 it will be subject to changes in
temperature and total pressure. The LI-610 pump lies upstream from the
condenser, and flow resistance due to the LI-610 plumbing and
downstream equipment causes a small over-pressure to develop in the
condenser, usually in the range of 0 - 6 kPa. At atmospheric pressures
above 80 kPa, the saturation vapor pressure in the condenser is virtually
independent of these small variations in total pressure, and, in any case,
they are taken into account by the enhancement factor.
The extent of this pressure dependence can be illustrated with the
following example. One way to express the enhancement factor is
f(T,P) = 1.00072 + 3.2 10-5P + 5.9 10-9 PT {dimensionless} 3-5
(Buck, 1981). Five kPa is a typical condenser over-pressure that might
occur if a high flow rate (1.5 liters min-1 ) is supplied to a gas exchange
system downstream from the LI-610. At 20 °C and P = 100 kPa, f(T,P) =
1.0039; at 20 °C and P = 105 kPa, f(T,P) = 1.0041, a negligible
difference. It is apparent from equation 3-5 that the enhancement factor
temperature and pressure dependence causes only small deviations from
the nominal value of 1.004 under normal conditions. f(T,P) varies from
1.0033 to 1.0043 over a pressure range of 80 kPa to 110 kPa, and a
temperature range of 0 °C to 50 °C.
However, a 5 kPa over-pressure in the condenser will have a much larger
effect on the vapor pressure measured downstream if the measuring
instrument is at atmospheric pressure. To demonstrate this, assume that
the downstream vapor pressure is measured in the LI-6262 CO2/H2O
Analyzer at 100 kPa total pressure, while the water vapor mole fraction
was established in the LI-610 at 105 kPa. The water vapor mole fraction
that was established in the LI-610 will be constant throughout the system
if there are no sources or sinks between the LI-610 and the measuring
instrument. Let the subscript "610" denote variables established in the
LI-610, and the subscript "meas" denote variables measured in whatever
instrument is used (e.g. LI-6262, etc.). Then, by definition, w610 =
e610/(P+P), and wmeas = emeas/P; but, w610 = wmeas, so
e meas =
3-8
Operation
P
e 610
P + DP
3-6
Section 3
Equation 3-6 shows that the same 5 kPa over-pressure now causes nearly
a 5% reduction in vapor pressure when measured in the LI-6262 (or other
instrument) at atmospheric pressure.
Errors due to condenser over-pressure can be minimized in two ways.
First, condenser pressure can be measured and an appropriate correction
can be applied using equation 3-6. This should be done when the LI-610
is used as part of a photosynthesis system, because high flow rates are
sometimes required, and the gas exchange system may have extensive
plumbing, both leading to significant condenser over-pressures.
A second method for minimizing condenser over-pressure is to use low
flow rates and a short flow path between the LI-610 and the watermeasuring instrument. This would be the normal configuration when
using the LI-610 to calibrate another instrument. The device to be
calibrated should be attached to the LI-610 with a short piece of tubing
with relatively large bore diameter [1/8 inch (3.2 mm) or larger], and the
flow rate should be kept low when the measurement is actually made
(0.25 liters per minute or less). A small condenser over-pressure may
still develop, but the condenser fill tube can be used to measure water
column height with sufficient accuracy to estimate the condenser
pressure. One centimeter of water is equivalent to 0.097 kPa, or about
0.1 kPa, at ordinary temperatures. See Section 4 for further information
about calibration protocols.
Operation 3-9
Section 3
Temperature Effects
It is not necessary to correct vapor pressure for temperature differences
that may occur between the LI-610 and the measuring instrument. Small
pressure differences may develop at points along the flow path due to
flow rate-dependent pressure drops, but pressure is constant at a given
point. Equation 3-1 can be rearranged to give P = RT, where = n/V =
mole density {mol m3}. If total pressure and composition are constant,
then the partial pressures of individual components, including water
vapor, are also constant. It follows that an increase in temperature will
cause a reduction in total gas density and the densities of individual
components, but no change in total pressure or vapor pressure.
Therefore, no vapor pressure corrections are necessary for temperature
differences that might occur in the system.
Relative Humidity
Calibration of relative humidity sensors is a principal use of the LI-610.
Relative Humidity {%} is defined as
RH =
e
× 100%
e(T)
3-7
where e is the prevailing vapor pressure of a parcel of moist air at
temperature T, and e(T) is the saturation vapor pressure at the same
pressure. Relative humidity is the ratio of the actual vapor pressure to the
maximum vapor pressure that can exist at equilibrium at a given
temperature.
It is often necessary to establish a known relative humidity at a known
temperature in some device. For example, one may want to calibrate a
relative humidity sensor, or establish a known RH in an airstream
entering a leaf photosynthesis chamber. This can be done using equations
3-4, 3-6 and 3-7, or done approximately using the psychrometric chart
given in Figure 3-2.
3-10
Operation
Section 3
Sample Calculations
Example 1. Assume you wish to calibrate a relative humidity sensor in
a leaf chamber where the air temperature is 23.0 °C. The LI-610 dew
point temperature is to be set so that the chamber relative humidity will
be 40%. We shall neglect flow-dependent pressure changes, for the
moment. The steps to solution are: (1) compute the saturation vapor
pressure at 23.0 °C using equation 3-4; (2) solve equation 3-7 for the
required chamber vapor pressure; and (3), solve equation 3-4 for the
required dew point temperature setpoint for the LI-610.
1. The saturation vapor pressure at 23 °C is
17.502 × 23
e(23°) = 0.61365e 240.97 + 23 = 2.820 kPa
2. The chamber vapor pressure must be
40% =
e
×100
2.82 kPa
e = 1.128 kPa
3. The LI-610 setpoint temperature necessary to give a vapor pressure of
1.128 kPa is equivalent to the dew point temperature corresponding to
a vapor pressure of 1.128 kPa. Solving equation 3-4 for T,
T=
240.97z
e
,where z = ln
17.502 − z
0.61365
Z = ln
1.128
= 0.6088
0.61365
T = 8.7 °C, the LI-610 setpoint.
The psychrometric chart in Figure 3-2 can also be used to find an
approximate solution. This is especially valuable when trying to quickly
find the LI-610 dew point temperature necessary to give a desired
incoming humidity while making photosynthesis measurements in the
field. With reference to Figure 3-2, find the chamber or device
temperature on the x-axis, read up to the desired humidity line and note
the vapor pressure on the y-axis. Then, at constant vapor pressure, read
across the chart to the left until the 100% RH curve is reached. Finally,
Operation 3-11
Section 3
read down to the corresponding temperature on the x-axis. This will be
the LI-610 setpoint temperature.
Example 2. Now, suppose we have a problem similar to Example 1, but
working at a flow rate of 1 liter per minute leads to a condenser overpressure of 2 kPa at a total barometric pressure of 97 kPa in the leaf
chamber. Assume the chamber temperature is 23.0 °C, and the desired
relative humidity is 40%, as before. The first two steps to solution are the
same as before; however, the pressure correction from equation 3-6 must
be inserted at step 3 before proceeding.
1. e(23°) = 2.820 kPa
2. The required chamber vapor pressure, e = 1.128 kPa.
3. The LI-610 vapor pressure required to give a chamber vapor pressure
of 1.128 kPa is computed by rearranging equation 3-6.
e meas =
P
e 610.
P + DP
So,
e 610 =
97 + 2
1.128 kPa = 1.151 kPa.
97
4. Finally, compute the LI-610 dew point temperature, as before, using
the vapor pressure from step 3.
T=
240.97z
e
, where z = ln
17.502 - z
0.61365
z = ln
1.151
= 0.6290
0.61365
T = 9.0 °C.
To achieve the desired RH in the leaf chamber, the LI-610 setpoint
temperature must be a little higher than before to correct for expansion of
the gas stream.
3-12
Operation
Section 3
Additional
Relationships
1. Combining equations 3-4, 3-6 and 3-7
17.502Td
P
e 240.97 + Td
RH = P + ΔP17.502T
× 100%
3-8
e 240.97 + T
where P = barometric pressure, P = condenser over-pressure, Td =
LI-610 dew point temperature, and T = measuring device
temperature. RH is the relative humidity that will hold in the
measuring device at T and P when the LI-610 is set to Td with overpressure P.
2. It is sometimes necessary to know the pressure-corrected dew point in
a measuring device given the LI-610 dew point temperature,
condenser pressure and barometric pressure. This can be found by
combining equations 3-4 and 3-6 and solving for device temperature.
T=
240.97[ln R + f(Td )]
17.502 − [ln R + f(Td )]
3-9
where T = the pressure-corrected dew point temperature in the
measuring device given the LI-610 dew point temperature setpoint,
Td; R = P/(P + P); and
f(Td ) =
17.502Td
240.97 + Td
Water Sorption
Water vapor adsorbs to the surface of all materials. Therefore, be sure to
allow ample equilibration times when calibrating humidity measuring
instruments, especially when large humidity changes are made.
Equilibration times on the order of an hour are not excessive when
performing careful calibrations.
Maximum Flow Rates
Our tests suggest that 2 liters per minute is about the maximum flow rate
that can be used with the LI-610 and still obtain complete saturation at
ordinary laboratory temperatures.
Operation 3-13
Section 3
Relative Humidity (%)
100 %
12
12.365
90
10
80
40%
Saturation
Vapor
Pressure
at TDP
9
Vapor Pressure (kPa)
100%
11
8
0
0
•
•
•
•
Vapor
Pressure
at Tair &
40% RH
70
0%
60
50
7
Dewpoint
Air Temp.
Temp., TDP T air
50
6
5
40
4
30
3
20
2
10
1
0
0
0
5
10
15
20
25
30
35
40
45
50
Temperature (°C)
Figure 3-2. Psychrometric Chart showing temperature, vapor pressure, and relative humidity.
3-14
Operation
Section 3
Table 3-1
Reference vapor
pressure (kPa)
Temp.
(°C)
pure
water
List
-40.00
-30.00
-20.00
-10.00
0.00
10.00
20.00
30.00
40.00
50.00
0.019
0.051
0.125
0.286
0.611
1.227
2.337
4.243
7.378
12.340
moist
air
Wexler
0.019
0.051
0.126
0.288
0.614
1.233
2.348
4.263
7.416
12.409
Vapor pressure (kPa)
computed from temperature (°C)
Temperature (°C) computed
from vapor pressure (kPa)
moist
air
Buck
Eq. 3-4
moist
air
Buck
Eq. 3-10
pure
water
Lowe
Eq. 3-11
pure
water
LI-COR
Eq. 3-12
Buck
Eq. 3-4
Buck
Eq. 3-10
LI-COR
Eq. 3-12
0.019
0.051
0.126
0.288
0.614
1.233
2.347
4.260
7.414
12.419
0.019
0.051
0.126
0.288
0.614
1.233
2.347
4.262
7.412
12.399
0.019
0.051
0.125
0.286
0.611
1.227
2.337
4.243
7.377
12.339
0.019
0.051
0.126
0.287
0.611
1.226
2.334
4.238
7.378
12.365
-39.85
-29.93
-19.97
-10.00
-0.00
10.00
20.01
30.01
40.01
49.98
-39.96
-29.98
-19.99
-10.00
-0.00
10.00
20.00
30.01
40.01
50.02
-39.88
-29.93
-19.95
-9.95
0.06
10.08
20.10
30.10
40.10
50.07
From Wexler's data using
17.502T
Buck (1981) : e(T) = 0.61365 e 240.97+T {kPa}
⎛ 18.729- T ⎞
⎝
227.3 ⎠
Buck (1981) : e(T) = 0.61121 [1.00072 + 3.2 × 10 -5 (P) + 5.9 × 10 -9 (PT)]e
T + 257.87
Lowe (1977): e(T) = a0 + T (a1 + T(a2 + T(a3 + T(a4 + T(a5 + a6T)))))
a0 = 0.61078
a1 = 0.044365
a2 = 1.4289 10-3
a3 = 2.6506 10-5
a4 = 3.0312 10-7
a5 = 2.0341 10-9
a6 = 6.1368 10-12
7.6448T
LI − COR(1990) : e(T) = 0.61083 × 10 242.62 + T
Operation 3-15
Section 3
References
Buck, A.L. 1981. New equations for computing vapor pressure and
enhancement factor. J. Appl. Meteor. 20: 1527-1532.
Goff, J.A., and S. Gratch. 1946. Trans. Amer. Soc. Heat. and Vent. Eng.,
Vol. 52, p. 95.
Hyland, R.W. 1975. A correlation for the second interaction virial
coefficients and enhancement factors for moist air. J. Natl. Bur. Stand.,
79A, 551-560.
LI-COR, inc. 1990. LI-6262 CO2/H2O Analyzer: Instruction Manual.
Publication No. 9003-59. LI-COR, inc.
List, R.J. 1966. Smithsonian Meteorological Tables, 6th rev. ed. The
Smithsonian Institution, 527 pp.
Lowe, P.R. 1977. An approximating polynomial for the computation of
saturation vapor pressure. J. Appl. Meteorol. 16:100-103.
McDermitt, D.K., 1990. Sources of error in the estimation of stomatal
conductance and transpiration from porometer data. HortScience 25(12):
1538-1548.
Wexler, A. 1976. Vapor pressure formulation for water in the range 0°
to 100° C. J. Res. Natl. Bur. Stand., 80A, pp. 775 ff.
3-16
Operation
Section IV.
Calibrating LI-COR Instruments
General Information
The LI-610 can be used to calibrate water vapor gas analyzers such as the
LI-COR LI-6262, LI-7000, LI-7500, and LI-840 CO2/H2O Gas
Analyzers, the gas analyzer in the LI-6400 Portable Photosynthesis
System, and instruments that use relative humidity sensors, including the
LI-COR LI-1600 Steady State Porometer, and the LI-6000 and LI-6200
Portable Photosynthesis Systems, among others. The LI-610 can also be
used to verify the calibration of dew point hygrometers.
An article written by LI-COR Applications Scientist Dayle McDermitt
(HortScience, Dec. 1990) discusses a variety of topics concerning
stomatal control of leaf conductance, including the effects of sensor or
calibration errors on the accuracy of conductance measurements, the
relationship between molar conductance units presently used and
velocity units used in older literature, as well as other considerations.
Reprints of this article are available on request from LI-COR.
Calibrating the LI-6400 H2O Analyzer
Setting the H2O Span
To check the span of the H2O analyzer, you’ll need a known
concentration of H2O, provided by the LI-610. The H2O IRGA gain
adjustment is a process by which the user can manually (using the arrow
keys ) adjust the values of Gwr and Gws (see Equations (14-5) and (146) on page 14-5 of LI-6400 Book 3).
Calibration
4-1
Section 4
To set the H2O Span
1.
Set up the LI-610 for an appropriate dew point
Subtract about 5 °C from room temperature,and use that for the target
dew point temperature. Wait until the condensor’s temperature (as
monitored on the LI-610) reaches this target. The reason for this 5
°C “buffer” is to avoid condensation in the line between the LI-610’s
condensor and the IRGA. If condensation happens, you will have
large errors.
2.
Set the flow rate
Use a flow rate of about 0.5 l min-1 from the LI-610.
3.
Attach to the IRGA
You have two choices, as shown in Figure 4-1. We recommend
option B: splitting the flow and connecting both the reference and
sample, with Match Off. The reason for this is that you will be able
to drastically reduce the equilibrium time, waiting for the sample
cell.
A
If you connect only to the sample port,
then Match must be ON for the air to
get to the reference analyzer as well.
PORTABLE
PHOTOSYNTHESIS SYSTEM
MODEL
LI-6400
SR. NO.
PSH-0001
B
If you split the flow, Match can be Off.
(By turning Match ON and Off while
watching the reference concentration,
you can see the influence of the sample cell and chamber on the air stream)
PORTABLE
PHOTOSYNTHESIS SYSTEM
MODEL
LI-6400
SR. NO.
PSH-0001
Figure 4-1. Flow from the LI-610 can be connected only to the sample port
of the LI-6400 sensor head (A), or can be split to both sample and reference
ports (B).
4-2
Calibration
Section 4
4.
View water channels
Press F3 or F4 to make the water IRGAs the active ones.
5.
Wait for equilibrium
Watch the rates of change (slopes). If you are using Option A
(connected to sample, Match On), then be prepared to wait about 20
minutes, until the rise in sample and reference concentration is
negligible. If you are plumbed for Option B (sample and reference
connected), ignore the sample, and only wait for the reference to
equilibrate. 3 to 5 minutes should be adequate.
6.
Adjust the reference gain as needed
When Td_R_°C is highlighted, press and to adjust the H2O
reference IRGA’s span factor until Td_R_°C reads correctly (Figure
4-6).
’
’
Adjusting H2O_R (use
)
CO2Sμml CO2Sμml Td_R_°C Td_S_°C
318.6
319.8
18.75
19.90 Mean
2.4E+0 4.5E+0 4.8E-2 3.1E-2 Slope
Fan:Fst
1.009
1.007
.997
.981 Mch:ON
CO2_R
CO2_S
H2O_R
H2O_S
Done
Figure 4-6. Adjusting the H2O span. Adjust until the displayed dewpoint
value (18.75 in the example above) matches the LI-610 set point.
7.
Select the sample IRGA
Press (or f4 )to highlight Td_S_°C.
If you are plumbed for Option B, continue with Step 8.
If you ’re plumbed for Option A, press and to adjust Td_S_°C
until it reads correctly. You are done.
8.
Match mode ON
Press M to make the Mch:indicator read ON.
Calibration
4-3
Section 4
9.
Note the reference dew point value
Watch the left hand (reference) Td_C value. It will likely drop a bit,
as the still unequilibrated air from the sample cell enters the
reference cell. When it stabilizes (30 seconds), set the sample IRGA
to read that value.
10. Quit and Save, if done
Press escape, and select "View, Store Zeros & Spans" now, if you
are done calibrating.
Calibrating the LI-7000 CO2/H2O Infrared Gas Analyzer
Preliminary
To avoid condensation problems choose a dew point temperature that is
about 3 to 5 °C below the ambient temperature. Also, since water vapor
sorbs and desorbs from surfaces, allow plenty of time for the reading to
stabilize, and minimize the surface area it has to absorb on (minimize
tubing lengths). It is important not to rush through water vapor
calibrations; give the surfaces plenty of time to equilibrate to large
changes.
The LI-7000 provides two convenient user interfaces for doing user
calibrations (Figures 4-2 and 4-3).
User Calibration
CO2Bμm/m
CO2Aμm/m
13.1
5.23
CO2 Action: [ <Do Nothing>
H2O Action: [ <Do Nothing>
1 Edit...
H2OAmm/m
2.234
More...
H2OBmm/m
4.387
]
]
Done
Figure 4-2. LI-7000 calibration function on instrument display.
4-4
Calibration
Section 4
Figure 4-3. Calibration dialog box in PC communications software.
The calibration dialog box allows you to define a calibration action to be
performed for CO2 and/or H2O. You then flow the appropriate gas(es)
through the appropriate cell(s), wait for the readings to stabilize, and then
press DoCO2 (f2) or DoH2O (f3) to execute the calibration action. For
the next 4 or 5 seconds, the LI-7000 will average the readings it is taking,
then perform the requested action.
There are three major choices for calibration actions:
1. Make cell A read...
2. Make cell B match cell A
3. Make cell B read...
The “Make cell A read...” option is designed to correct the drift with time
that occurs while in Reference Estimation Mode (REM). (This action is
not available from the front panel unless you are in REM.) You perform
this procedure while temporarily flowing a known concentration through
cell A. Any concentration will work, even 0.
Calibration
4-5
Section 4
The “Make cell B match cell A” option is the most common procedure.
You flow the same air through both cells and execute this procedure to
remove the effects of dirt and other sources of error. You don’t need to
know the actual concentration of this gas, but it should be stable. There is
a subtlety here: if you match the cells at one concentration, you may find
that the cells are no longer matched at a different concentration. The
LI-7000 can adjust for this common mode drift: match first with a (near)
zero concentration, then match again at the higher concentration, and the
IRGA should then be reasonably well matched between those two
concentrations.
The “Make cell B read...” adjusts the span parameter for the calibration
polynomial, and should only be used when the cell A concentration is
known (that is, don’t do this while in REM). NOTE: You can use any
concentration in the B cell to do this - even 0; just make sure that there is
a significant difference between the cell A and B concentrations.
Calibration
Instructions
The type of user calibrations that are appropriate depend on what
operating mode you are using, and there are basically three:
I. Reference (Cell A) Is Known and Constant
A constant, known concentration is continually flowing through cell A.
The source may be scrubbed air, or air from a tank, or air from a dew
point generator.
II. Reference (Cell A) Is Known, but not Constant
The cell A air stream is being measured by an external analyzer, which is
communicating the concentration to the LI-7000 through an auxiliary
input. The concentration changes with time, but it is always being
measured.
III. Reference (Cell A) is Estimated
This is Reference Estimation Mode (REM). The LI-7000 is continually
providing its best estimate of the cell A concentration. The cell B
concentration will have the same error as the cell A concentration, so the
differential value will be more accurate than either individual cell’s
accuracy.
4-6
Calibration
Section 4
The calibration instructions for these three operating modes are described
next.
I. Reference (Cell A) Is
Known and Constant
If you will be flowing a known, constant concentration gas though the A
cell, there are two user calibrations that you may want to do.
1 Point Match (periodically)
Put the cell A gas through cell B to match the cells (Box 1, below). This
counteracts drift and dirt effects.
Span (optional)
Put a known concentration (and different from cell A) in cell B, and
calibrate (Box 3, below).
II. Reference (Cell A)
Is Known, but not
Constant
If during operation, cell A will have a range of known concentrations, a
potential problem with common mode drift arises. This can be
minimized by adding a 2 Point Match to the list of calibrations. (Note
that during any calibration, the cell A and B concentrations must be
stable.)
2 Point Match (initially)
Match first with scrubbed air in both cells, then again with a typical cell
A concentration in both cells (Box 2, below). This will characterize the
common mode drift in order to minimize the effect on matching of a
changing reference concentration.
1 Point Match (periodically)
Put the current cell A gas through cell B to match the IRGA (Box 1,
below). This counteracts drift and dirt effects.
Span (optional)
Put a known concentration (different from cell A) in cell B, and calibrate
(Box 3, below).
Calibration
4-7
Section 4
III. Calibrating for
REM Operations
If you are going to be operating with an unknown concentration of gas
flowing though the A cell, there are two calibrations that you will need to
do periodically.
Calibrate Cell A (initially, and periodically thereafter)
The cell A calibration (Box 4, below) is critical to how REM works.
After that, experience will tell you how often it needs to be redone; the
period might range from hours to days, depending on conditions, such as
temperature.
1 Point Match (periodically)
Put the cell A gas through cell B to match the cells (Box 1, below). This
counteracts drift and dirt effects.
4-8
Calibration
Section 4
Box 1
Box 2
One Point Match
This procedure will match the cells at a single
concentration.
1.
Flow the target gas through cells A and
B simultaneously.
Pressures, temperatures, and water
concentrations should be the same.
2.
Set both H2O and CO2 actions to
"Make cell B match cell A.
3.
When stable, press "DoH2O".
After about 5 seconds, the H2O readings
for A and B should match. (Always do
H2O first, since the CO2 calculations
depend on H2O being correct).
4.
Press "DoCO2".
After about 5 seconds, the CO2 readings
for A and B should match.
Two Point Match
The two point match will match the cells at a
low and a high concentration. The low
concentration should be <20 μmol/mol for
CO2 (<3 mmol/mol for H2O); the high
concentration should be near the upper end of
where you are planning to operate cell A.
1.
Set reference to 0.
Temporarily set the operating mode to 0
(or dry) air in the reference cell. (If
reference is being measured externally,
you won't have to do this).
2.
Do a "1 Point Match" with 0 (dry) air.
This matches the cells at a low
concentration.
3.
Change reference to the high
concentration.
If reference is being measured externally,
you won't have to do this.
4.
Do a "1 Point Match" at the high
concentration.
This matches the cells at a high
concentration. The match should be
reasonably good between the two.
Calibration
4-9
Section 4
Box 3
Box 4
Setting the Span
Calibrate Cell A
Make sure you have done a one or two point
match first.
1.
Flow reference gas through A, and the
span gas through B.
The concentrations must be different.
This procedure is necessary periodically while
in REM (Reference Estimation Mode)
operations.
1.
Flow a known gas through cell A.
Any concentration (including 0) is fine.
2.
Set CO2 (or H2O) action to "Make cell
B read..."
You'll be prompted for the cell B target
value.
2.
Pick "Make cell A read..." for CO2 (or
H2O).
You will be prompted for the
concentration.
3.
Wait for stability, then press "DoCO2"
(or "DoH2O").
After about 5 seconds, the cell B reading
should be on target.
3.
Press "DoCO2" (or "DoH2O").
After 5 or 6 seconds, cell A should be
reading the target value.
User Calibration
Example
4-10
Calibration
Example 1. Reference Estimation Mode (REM) for both CO2 and H2O.
REM is used when precise differential concentrations are required and
where absolute accuracies are less important. In this example a tank of
gas of 370 μmol/mol CO2 in dry air is used for the CO2 calibration. The
LI-610 is used to provide an airstream with known dew point to Cell A
for the H2O calibration. A periodic user calibration procedure for
operating the LI-7000 in REM is given below.
1.
Flow the calibration gas through both cells of the LI-7000 optical
bench.
2.
Press Shift + 1 to display the calibration group labels.
3.
Press the SetRef key (f1). The Reference Cell Options are
displayed. Press Edit (f1) to edit the CO2 options. Choose
Estimated . Press OK . Repeat for H2O, and edit the H2O units box
to display the desired units (°C).
Section 4
4.
Press the Calib key (f4). In the H2O Actions box, highlight 'Make
cell A read...' and press OK.
5.
Highlight 'Exact value' and press OK (f5). Enter the dew point of
the airstream provided by the LI-610, and press OK (f5).
6.
Press the DoH2O key (f3) and wait for about 5 seconds. Cell A will
now read the H2O value entered above.
7.
Press the Calib key (f4). In the H2O Actions box, highlight 'Make
cell B match cell A' and press OK .
8.
Press the DoH2O key (f3) and wait for about 5 seconds. The cell B
reading will be matched to the H2O value of cell A.
9.
Press the Calib key (f4). In the CO2 Actions box, highlight 'Make
cell A read...' and press OK.
10. Highlight 'Exact value' and press OK . Enter a target value of 370
and press OK.
11. Press the DoCO2 key (f2) and wait for about 5 seconds. Cell A will
now read 370 μmol/mol.
12. Press the Calib key (f4). In the CO2 Actions box, highlight 'Make
cell B match cell A' and press OK .
11. Press the DoCO2 key (f2) and wait for about 5 seconds. Cells A and
B will now read 370 μmol/mol.
12. Press Done (f5).
Calibration
4-11
Section 4
Calibrating the LI-7500/A CO2/H2O Infrared Gas Analyzer
Preliminary
To avoid condensation problems choose a dew point temperature that is
about 3 to 5 °C below the ambient temperature. Also, since water vapor
sorbs and desorbs from surfaces, allow plenty of time for the reading to
stabilize. It is important not to rush through the water vapor calibration.
If it is more convenient, CO2 and water vapor zero and span calibrations
can be done separately. In general, if reliable calibration standards are
not available or if there is not enough time to do the job properly, it is
better to leave the zero and span settings alone than to rush through the
procedure and make incorrect settings.
1.
Run the LI7500 software program. Select the Calibration tab in the
Main Window of the 7500-50 Communications software.
2.
Place the calibration tube into the sensor head as shown in Figure 4-4
and connect the temperature sensor cable to the LI-7500 control box.
Calibration Tube
(insert this end first)
Thermistor
Air Out
Pressure
(optional)
Air In
Figure 4-4. Flow calibration gas at the Air In port shown.
4-12
Calibration
Section 4
Insert the top of the fixture first, and slide the bottom into place. It
is very important that the fixture is centered between the windows
covering the source and detector modules. It can be helpful to
click on the Diagnostics tab in the 7500-50 software, and view the
AGC value while centering the fixture; if the AGC value increases
when the fixture is in place, it indicates that one or both of the
windows are partially or totally obscured. Move the fixture back
and forth until the AGC value reads the same value as before the
fixture was inserted. The fixture is very easy to center; if it looks
centered, it probably is.
NOTE: The three ports on the calibration tube are entirely
interchangeable.
3.
Click on the Calibration tab, and verify that temperature and
pressure sensors are working properly. (If you are using an
alternate source for temperature and pressure values, click on the
Inputs tab and set that up).
IMPORTANT NOTE: Always zero the instrument before
spanning (don’t span, then zero).
4.
Flow CO2-free air through the calibration fixture at a rate of about
0.5 to 1.0 LPM. Attach the zero gas to the calibration fixture at
one of the ports shown in Figure 4-4.
Calibration
4-13
Section 4
Zero CO2
5.
Observe the CO2 concentration and wait for it to stabilize
(typically 1 minute). Also, note the present value of Zco (Figure 45).
Note this value
Figure 4-5. Note value of Zco, shown as Current Value.
6.
When the reading has stabilized, click Zero to set the CO 2 zero.
After a brief delay, the displayed CO2 value should be fluctuating
around zero. Check the resultant value of Zco shown on the Zero
CO2 page (Figure 4-5). It should be near 1 (typically between 0.85
and 1.1). This value will steadily increase as the internal
chemicals lose effectiveness.
7.
Now is a good time to check or set the H2O zero, if you have been
flowing dry, CO2-free air through the optical path. Click the H2O
tab, and note the present value of Zwo .
8.
Wait for the H2O reading to stabilize (3 or 4 minutes).
9.
Click Zero. Note the new value of Zwo (typically between 0.65
and 0.85).
Zero H2O
Span CO2
10. Flow a CO2 span gas through the calibration tube at 0.5 to 1
liter/minute.
4-14
Calibration
Section 4
11. Click on the CO2 Cal tab. Enter the mole fraction in the target
entry.
12. When stable (1-2 minutes) click Span.
Check the value of Sc
(typically 0.9-1.1).
Span H2O
13. To set the H2O span, flow air of known dew point through the
calibration tube at about 0.5 to 1.0 LPM. To avoid condensation,
use a dew point temperature several degrees below the ambient
temperature.
14. Click the H2O tab, and note the present value of Sw. Enter the
span gas dew point temperature in the target entry.
15. Observe the H2O dew point and wait for it to stabilize. This may
take up to 15 or 20 minutes.
16. When the reading has stabilized, click Span . Note the value of Sw
(typically 0.9-1.1).
Calibration
4-15
Section 4
Calibrating the LI-840/A CO2/H2O Infrared Gas Analyzer
Run the 840-500 Windows software program, and select Calibration
from the View menu. The Calibration window is the area in which you
set the zero and span of the LI-840.
It is recommended that you perform the zero calibrations first, followed
by the span calibrations. To zero, flow a dry, CO2-free gas through the
LI-840/A, and make sure the optical cell is completely purged. Press the
Zero CO 2 button.
The display will show ZERO, and the text in the Calibration window is
greyed out. The zero will be set electronically, and the current date will
be entered in the "Last zeroed on" field when completed. Repeat for the
H2O channel.
To span, connect a span gas of known concentration to the input air
stream. Make sure the cell is purged, enter the value of the span gas, and
click on Span CO2.
4-16
Calibration
Section 4
The display will show SPAN, and the text in the Calibration window is
greyed out. The span will be set electronically, and the current date will
be entered in the "Last spanned on" field when completed. Repeat for the
H2O channel using the LI-610 to provide the airstream with known dew
point.
Calibrating the LI-6262 CO2/H2O Infrared Gas Analyzer
Preliminary
If present, remove the blue Balston filters from inside the LI-6262 and
replace them with the Gelman disc filters supplied in the spare parts kit.
The Gelman filters will not fit inside the LI-6262 case; they must be
placed in the airstream just before it enters the analyzer. Under no
circumstances should the LI-6262 be operated without filtering the air
before it enters the analyzer.
The protocols suggested here for setting zero and span assume that high
accuracy is desired, so they have long equilibration times. Experience
with CO2 analyzers causes one to expect rapid and stable responses to
changes in gas concentration; however, this will not be the case with
water vapor.
Working with water vapor presents difficulties due to water vapor
sorption that are not encountered with CO2. These problems will cause
the LI-6262 to appear to drift or respond slowly to changes in humidity.
The resolution of the LI-6262 is beyond that obtainable with most other
humidity measuring instruments, even dew point hygrometers; so very
small humidity changes can now be seen, which in the past were largely
unobservable. High sensitivity coupled with water sorption, temperature
variations, pressure effects, etc. may cause complete stability to be
elusive.
We suggest, therefore, that you determine in advance the accuracy that is
required, and then establish the equilibration time necessary to meet your
requirements. The equilibration times given in these protocols are meant
only as starting points.
Calibration
4-17
Section 4
Absolute Mode H2O
Zero Calibration
Absolute Mode H20
Span Calibration
4-18
Calibration
The protocols for setting zero and span in Absolute Mode and
Differential Mode are quite similar.
1.
Turn on the LI-6262. Change the chopper desiccant and soda lime if
necessary.
2.
Pass dry air from a compressed air source or from anhydrous
magnesium perchlorate into the analyzer sample and reference cells.
You may find that air from a tank of compressed gas contains a very
small amount of water vapor, especially if tank pressure is low. Use
anhydrous magnesium perchlorate after the tank, if necessary.
3.
If the LI-6262 is not equipped with a pressure transducer (check at
FCT 43), enter the current barometric pressure into Function 77, and
also enter WREF = 0 (Function 02 or 68).
4.
The analyzer and flow path will dry down faster at higher flow rates.
We suggest you use 1 liter min-1 dry air for 20 to 30 minutes through
both sample and reference cells; then reduce the flow rate in both
cells to 0.25 liters min-1 for 10 to 20 minutes prior to setting zero.
Set zero.
1.
Set the LI-610 to a dew point corresponding to about 80% RH at
ambient temperature. This typically means that the dew point
temperature should be set 3 to 5 °C below the ambient room
temperature. This will prevent local temperature fluctuations in the
gas exchange system from causing condensation.
2.
Set the LI-610 flow rate to about 1 liter min-1. and allow moist air to
pass through the analyzer for about 20 minutes. Reduce the flow rate
to about 0.25 liters min-1 for an additional 20 minutes, or until the
signal is adequately stable.
3.
Read the pressure differential between the condenser and
atmosphere. Compute the condenser vapor pressure using equation
3-4, and then correct it for condenser over-pressure using equation
3-6. Set the LI-6262 span to read the vapor pressure computed from
equation 3-6.
Section 4
You may now wish to check an intermediate vapor pressure. You
will find that the system will equilibrate more quickly with smaller
water vapor changes.
No further span adjustments will be necessary for either absolute or
differential operation. However, if you wish to operate in differential
mode it will be necessary to reset the zero each time a new reference
gas is passed through the LI-6262 reference cell.
Differential Mode H2O
Zero Calibration
It is only necessary to set zero in differential mode. The analyzer gain is
set with a span adjustment in Absolute Mode. No further span
adjustments are necessary for operation in Differential Mode because the
calculations automatically correct for analyzer sensitivity changes due to
different reference cell humidities.
1.
Set zero and span in Absolute Mode, as described above.
2.
Flow a reference gas through both the reference cell and sample cell
for 20 min at about 1 liter min-1. Reduce the flow to 0.25 liters min-1
for an additional 20 minutes, or until the displayed water vapor
differential is sufficiently stable.
3.
Enter the reference cell water vapor mole fraction WREF in units of
mmol/mol. WREF is computed from the dew point temperature T as
WREF = 1000
4.
Precautions
e(T)
P + DP
Adjust the displayed water vapor differential (channels 33, 35 or 37)
to read zero.
Pressure influences CO2 and water vapor infrared absorptance by
altering gas density, and by changing the absorption per mole of gas.
Therefore, careful attention must be paid to pressures in the analyzer.
The barometric pressure should be accurately measured and entered into
the instrument. All LI-COR CO2 and H2O analyzers are calibrated in
terms of mole fraction because this has been found to give the best
results, as theory predicts.
Calibration
4-19
Section 4
Span adjustments can be used to correct the CO2 or H2O mole fractions if
pressure is entered incorrectly, or if a nominal value is used; however,
subsequent conversions to partial pressure will be incorrect if they are
computed from an incorrect barometric pressure.
The span of all LI-COR infrared gas analyzers will vary with barometric
pressure changes because infrared absorptance varies with pressure.
Therefore, an electronic barometer should be used to provide accurate
barometric pressure data to the LI-6262 (or other analyzer) if continuous
recordings of CO2 and/or H2O vapor concentrations over long periods of
time are required. Note also, that some zero shift can be expected with
changes in analyzer temperature.
Pressure in the analyzer optical bench varies with gas flow rate. It
follows that span settings should be made at the same flow rate as
measurements, whenever possible. Further, the calculations in the
LI-6262 use the same pressure for both sample and reference cells.
Therefore, flow rates and total pressures should be the same in the two
cells.
In practice, flow dependent over-pressures in the sample and reference
cells will be small when flows are low (about 1 liter min-1, or less) and
the analyzer is vented directly to the atmosphere. However, large
pressure differences between the two cells that could occur with high
flow rates (> 5 liters min-1) cannot be accommodated by span adjustments
or on-board calculations. Presumably, large pressure differentials
between sample and reference cells could be included in calculations
outside the LI-6262, but this has not been tested.
Calibrating the LI-1600 Steady State Porometer RH Sensor
Initial Setup
4-20
Calibration
1.
Set the LI-610 dew point to 0.05 °C.
2.
Remove the LI-1600 console from the case as described in Section 5
of the LI-1600 instruction manual. For your safety, do not operate
the LI-1600 from AC power while performing this procedure.
Section 4
Calibration: Setting
the Zero
3.
Locate the zero and span potentiometers on the bottom console
circuit board. See the LI-1600 instruction manual (p. 5-10, Rev. 6)
for the location of these potentiometers.
4.
Remove the silica gel from the sensor head silica gel desiccant pack.
Leave the cap from the desiccant pack off to minimize back pressure.
5.
Connect a 3" (7.5 cm) length of 1/16" (1.59 mm) ID teflon tubing to
the small hose barb on the cuvette exit port. The tip of this barb is
recessed, and can be seen through the hole in the front of the LI-1600
sensor head shroud. The LI-610 will be connected to the sensor head
by inserting the teflon tube into the 1/8" (3.17 mm) ID Bev-a-line
tubing connected to the LI-610.
6.
Turn the LI-1600 ON, but do not press the "HUM SET" button.
7.
Replace the chamber aperture cap with the solid calibration cap
included with the 610-02 RH Calibration Accessories kit.
Alternatively, a sheet of non-porous, non-water-absorbing material
can be clamped over the aperture. Closed cell polyethylene foam is a
good material to use for this procedure, in the absence of the 610-02.
1.
Set the LI-610 flow rate to about 0.2 to 0.3 liters per minute. This
low flow rate is necessary to minimize the flow-related
pressurization of the LI-610 condenser.
2.
Check for condenser pressure changes:
• Turn off the flow and open the condenser fill/drain tube port. Note
the location of the fill tube water meniscus.
• Turn on the flow, regulate the flow to the recommended level, and
measure the change in meniscus height. CAUTION: Water will
squirt out of the fill tube if the LI-610 pumps against a lot of back
pressure at high flow rates. It may be necessary to put a vertical
extension tube on the fill/drain port, and/or reduce the flow rate
accordingly.
Calibration
4-21
Section 4
• Calculate the flow-dependent condenser pressure as P = 0.0979
kPa cm-1 (water column height, in cm). This pressure factor will
be used later.
Calibration: Setting
the Span
4-22
Calibration
3.
The LI-610 should be generating a dew point of 0.05 °C. The air
stream water vapor pressure will be about 0.61 kPa. Any remaining
water vapor can be removed by placing a tube of freshly dried silica
gel (oven dry at 175 °C for 1 hour) or anhydrous Mg(ClO4)2 between
the LI-610 and the LI-1600 sensor head. Alternatively, one could
use a tank of compressed air or nitrogen as the source of dry air.
4.
Allow this dry air to flow through the LI-1600 cuvette chamber for
about 60 minutes. Adjust the zero potentiometer so the display reads
2% RH if silica gel is used, or 0% if Mg(ClO4)2, compressed air, or
nitrogen is used.
The LI-1600 will not display negative values. If you are using a
compressed air tank and the display reads zero, adjust the potentiometer
until the display shows a small positive number, and then turn the
potentiometer down until the display reads zero, and the null meter is
centered.
1.
Remove the Mg(ClO4)2 or silica gel tube from the air line
connecting the LI-610 to the LI-1600.
2.
Note the LI-1600 cuvette temperature, Tc on the LI-1600 console
display.
3.
Find the dew point temperature Td that corresponds to 80% RH at
the cuvette temperature Tc using the psychrometric graph provided.
For example, to obtain 80% RH at Tc = 25 °C, set Td = 21.3 °C.
4.
Flow the air from the LI-610 through the cuvette for about 60
minutes. At the end of this time period, note the cuvette temperature
Tc, and the LI-610 dew point temperature Td.
5.
Compute the exact RH to which the span should be set. If the vapor
pressure is generated at an elevated pressure, as occurs in the dew
point generator condenser, a pressure correction must be applied
when vapor pressure is measured at atmospheric pressure. The
Section 4
relative humidity in the LI-1600 cuvette at temperature Tc and
pressure P (assumed atmospheric) when supplied with air generated
at dew point Td and pressure P + P is given by
17.502Td
4-1
P
e 240.97 + Td
P
+
DP
RH c =
× 100%
17.502T
c
e
6.
240.97 + Tc
Adjust the LI-1600 span potentiometer (see Section 5 of the LI-1600
Manual for location of the span potentiometer) until the display reads
RHc within 0.4% RH. The display resolution is 0.4%, so don’t be
concerned if you cannot match the sensor display with the incoming
RH beyond this level of precision.
EXAMPLE: If the cuvette temperature Tc is 24 °C, the dew point
temperature Td is 21 °C, and the change in condenser pressure
between no flow and the actual flow is 3 cm of water at a barometric
pressure of 100 kPa, then equation 4-1 becomes
RH c =
Check Intermediate
Values
0.997e1.403
× 100% = 83.1%
e1.5853
Conduct the following procedures without further adjustment to the span
potentiometer.
1.
Find the dew point temperature that corresponds to about 50% RH at
ambient temperature using the psychrometric charts in Appendix C.
2.
Set the LI-610 to the dew point temperature and allow 60 minutes to
elapse after Td is reached.
3.
Calculate the exact cuvette RH using equation 4-1 and compare the
result to the displayed RH. They should agree to within ± 3% RH.
4.
Reset the LI-610 to a dew point corresponding to about 20% RH.
Repeat steps 2 and 3.
Calibration
4-23
Section 4
5.
Repeat the calibration procedure if there is a deviation of greater than
3% RH. If you find that intermediate RH values read consistently
low, set the span RH 1% higher than the calculated value. For
example, if the span RH is actually 80%, set the span to 81%, and
repeat steps 1 through 4.
Calibrating the LI-6200 or LI-6000 Portable Photosynthesis
System Humidity Sensor
Precalibration
1.
Set the LI-610 dew point to 0.05 °C.
2.
Mount the LI-6200 or LI-6000 sensor housing in a vise, if possible.
Unhook the leaf temperature thermocouple from the monofilament
support lines, and then remove the chamber from the sensor
housing.
BE VERY CAREFUL NOT TO TOUCH, SCRATCH, OR SMOKE
NEAR THE EXPOSED HUMIDITY SENSOR.
4-24
Calibration
3.
Check to be sure that the sensors and the exposed parts of the sensor
housing are clean and free of debris.
4.
Attach the nickel-plated aluminum block (included in the 610-02 RH
Calibration Accessory Kit) to the sensor housing (Figure 4-6) and
tighten it down. Allow the leaf temperature thermocouple to hang
free outside the aluminum block. The sensor head O-ring will seal
around the thermocouple wires sufficiently well to prevent serious
leaks.
Section 4
610-02
Sensor Housing
Hose Barbs
Figure 4-6. Nickel-plated aluminum block attached
to LI-6200 or LI-6000 sensor housing.
5.
Remove the top plate from the sensor housing by removing the four
corner screws. Locate the zero and span potentiometers in the
LI-6200 or LI-6000 sensor housing, as shown in Figure 4-7 below.
RH ZERO
RH GAIN
Figure 4-7. Location of the zero and span potentiometers in the LI-6200
or LI-6000 sensor housing.
6.
Disconnect the two Bev-a-line hoses from the barbs protruding from
the sensor housing, and connect one end of a 12” (300 mm) length of
1/8” (3.17 mm) ID Bev-a-line tubing to one of the hose barbs (either
barb will work), and the other end to one of the LI-610 output ports.
Calibration
4-25
Section 4
Calibration: Setting
the Zero
7.
Make sure that the sensor housing cable is connected to the console
(the cable from the LI-6200 console to the LI-6250 IRGA need not
be connected), and turn on the console.
1.
Set the LI-610 flow rate to approximately 0.2 to 0.3 liters per
minute. This low flow rate minimizes flow-related pressurization
within the LI-610 condenser. To check for condenser pressure
changes:
• Turn off the flow and open the condenser fill/drain tube port. Note
the location of the fill/drain tube water meniscus.
• Turn on the flow, regulate the flow to the recommended level, and
measure the change in meniscus height.
• Calculate the flow-dependent condenser pressure as P = 0.0979
kPa cm-1 water column height (in cm). This pressure factor will
be used later.
2.
For the LI-6200, the humidity lookup table (FCT 47) should match
the values given on the factory calibration sheet. The multiplier
value (FCT C7) should also read 0.024414. For the LI-6000, set the
system parameters for use with a desiccant as follows:
WINT = 0
W SLP = 0
FLOW = 0
RH IN = 0
CORR RH = Y
3.
4-26
Calibration
The LI-610 should be generating a dew point of 0.05 °C. The air
stream water vapor pressure will be about 0.61 kPa. Remove the
remaining water vapor from the air by connecting a tube of fresh
anhydrous Mg(ClO4)2 between the LI-610 and the sensor housing.
Alternatively, one could use a tank of compressed air as the source of
dry air; however, it may still be desirable to use a desiccant between
the tank and the sensor housing, especially if the tank pressure is low.
Section 4
Calibration: Setting
the Span
4.
Allow dry air to flow through the sensor housing for about 60
minutes. Identify the zero potentiometer again, and adjust so that the
display reads -0.7% RH.
1.
Remove the Mg(ClO4)2 from the air line connecting the LI-610 to
the sensor housing.
2.
Note the sensor chamber temperature Tc (from the console key
TCHAM).
3.
Find the dew point temperature Td that corresponds to 80% at the
cuvette temperature Tc using the psychrometric graph provided. For
example, to obtain 80% R.H. at Tc = 25 °C, set Td = 21.3 °C.
4.
Flow air from the LI-610 through the sensor chamber for about 60
minutes. At the end of this time period, note the chamber
temperature Tc, and the LI-610 dew point temperature Td.
5.
Compute the exact RH to which the span should be set. This can be
done using equation 4-1.
A pressure correction must be applied when the vapor pressure is
established in the dew point generator condenser at an elevated
pressure, and measured in the calibration block at atmospheric
pressure. Equation 4-1 gives the relative humidity in the calibration
block at temperature Tc and pressure P (assumed atmospheric), when
it is supplied with air having dew point Td established at pressure
P + P.
6.
After 60 minutes, adjust the sensor housing span potentiometer so
that the display reads RHc. Be sure that the cuvette temperature Tc is
used in equation 4-1.
EXAMPLE: If the cuvette temperature Tc is 24 °C, the dew point
temperature Td is 21 °C, and the change in condenser pressure
between no flow and the actual flow is 3 cm of water at a barometric
pressure of 100 kPa, then equation 4-1 becomes
Calibration
4-27
Section 4
RH c =
Check Intermediate
Values
0.997e1.403
× 100% = 83.1%
e1.5853
Conduct the following procedures without further adjustment to the span
potentiometer.
1.
Find the dew point temperature that corresponds to about 50% RH at
ambient temperature using the psychrometric graph supplied.
2.
Set the LI-610 to the dew point temperature and allow 60 minutes to
elapse after Td is reached.
3.
Calculate the exact cuvette RH using equation 4-1 and compare the
result to the displayed RH. They should agree to within ± 3% RH.
4.
Reset the LI-610 to a dew point corresponding to about 20% RH.
Repeat steps 2 and 3.
5.
Recheck the zero and span if there is a deviation of greater than ± 3%
RH. If the intermediate RH deviations are too large when the zero
and span are set correctly, you may wish to make adjustments to the
LI-6200 RH Calibration Table (FCT 47) to correct for sensor nonlinearity (see p. 7-14 of the LI-6200 Technical Reference Manual).
No such table exists for the LI-6000. If you encounter this problem
with the LI-6000, it may be desirable to adjust the span to read a little
high, if intermediate values are consistently low. It is unlikely that
intermediate values will be consistently high. For example, if an
intermediate value corresponding to an actual RH of 56% reads 52%,
try setting the span to 81%, etc. However, keep in mind that RH
errors at high humidities have larger effects on conductance
measurements than those at intermediate humidities.
4-28
Calibration
Section 4
Calibrating Relative Humidity Sensors (General)
The LI-610 can be used to calibrate a wide variety of relative humidity
sensors, in much the same manner as described earlier for calibrating the
humidity sensors in the LI-1600 and LI-6200. There are many types of
relative humidity sensors; in principle, they can be calibrated with the
LI-610 if certain basic procedures are followed.
First, the sensor should be enclosed in a chamber so that the LI-610 can
provide a constant source of water vapor to the sensor. Secondly, the
temperature of the chamber which houses the sensor must be monitored,
to accurately gauge the relative humidity present.
See Sample
Calculation #1, page 3-10 for an example of how to perform a calibration
for a relative humidity sensor.
Follow the manufacturer’s recommendations for making any adjustments
(i.e., potentiometers) necessary for calibrating your particular humidity
sensor.
Calibrating Dew Point Hygrometers (General)
As with relative humidity sensors, the configuration of dew point
hygrometers is widely variable. We hesitate to recommend specific
calibration procedures for dew point hygrometer heads with which we are
unfamiliar. In principle, however, the LI-610 can be used to provide
moist air with a known dew point (± 0.2 °C) that can be used as a
benchmark to test a dew point hygrometer. Follow all manufacturer’s
recommendations for further calibration procedures.
References
Buck, A.L. 1981. New equations for computing vapor pressure and
enhancement factor. J. Appl. Meteor. 20: 1527-1532.
McDermitt, D.K., 1990. Sources of error in the estimation of stomatal
conductance and transpiration from porometer data. HortScience 25(12):
1538-1548.
Calibration
4-29
Section V.
Maintenance
Draining the LI-610
The LI-610 should be completely drained before being shipped, or stored
for long periods of time. This will prevent the possibility of freezing,
algal growth, chemical corrosion, etc.
Condenser Block
To drain the condenser block:
•
Remove the threaded capnut attached to the fill/drain tube on the top
of the condenser block assembly.
•
Attach a male Luer lock to the fill/drain fitting on the condenser
block.
•
Connect a short section of Bev-a-line tubing with a female Luer lock
(included) to the male Luer lock on the condenser block housing.
•
Thread the female Luer lock into the 30 ml syringe.
•
Use the syringe to draw the water out of the condenser block. The
block holds approximately 20-25 ml of water when full.
Alternatively, the condenser block can be drained by plugging the two
output ports on the instrument front panel. Attach the section of Bev-aline tubing to the fill/drain fitting as described above. Close the flow
adjust valve completely. Turn the power switch and the air pump ON,
and open the flow adjust valve slightly to force the water out through the
fill/drain tube. Leave the air pump on until all of the water has drained
out of the condenser block.
Maintenance
5-1
Section 5
Radiator Assembly
Follow these steps to drain the radiator/cooler assembly; it is not
necessary to remove the LI-610 cover to drain the radiator.
•
Disconnect the tubing attached to the FROM COOLER and TO
CONDENSER fittings.
•
Attach a short piece of tubing between these same two fittings.
•
Turn the air pump ON and open the flow adjust valve. This will
force air through the radiator assembly, causing the water to flow
out of the tube which was previously attached to the FROM
COOLER fitting.
•
Leave the air pump ON until all of the water has been purged from
the system.
Internal Air Filter
The frequency with which the Balston air filter needs to be replaced will
depend upon the operating environment; it will generally need
replacement after 6 months to 1 year. The filter is located inside the LI610, on the hose leading from the AIR IN fitting, as shown in Figure 5-1.
Grade
BALSTON
DFU®
Before installing a new filter, blow clean dry air through it to remove any
fibers or other debris that may be loose inside.
The old filter can be easily removed by pressing the red ring toward the
center of the connector and pulling it off of the filter. Leave the connector
attached to the hose, as repeated removal from the hoses may result in a
leak. The filters may also be removed by inserting a pair of long-nose
pliers between the coupling and the filter; gently pry the two apart.
Install the new filter with the white directional arrow facing away from
the AIR IN fitting (Figure 5-1).
Spare filters can be ordered from LI-COR under part number 300-01961
(1 each).
5-2
Maintenance
Condenser
Fill/Drain
Port
Air Input
Internal Water
Filter Screen
Radiator
Fill
Internal Air
Filter
Figure 5-1. LI-610 interior.
Internal Water Filter Screen
A wire mesh filter screen is present on the internal side of the TO
COOLER fitting (Figure 5-1). This screen should be checked monthly, as
a clogged screen can severely limit the flow of cooling water through the
system.
To clean the internal water filter screen:
• Remove the cover of the LI-610 to gain access to the filter screen.
The radiator does not need to be drained to clean the filter screen.
• Place a towel under the large hose internal to the TO COOLER fitting
to absorb the small amount of water which will run out of the tubing.
Maintenance
5-3
Section 5
• Remove the hose, wipe the contaminants off the screen, and
reassemble.
External Fan Filter
The external fan filter should be cleaned (rinsed out) or replaced as
needed. The filter is located behind the black filter cover on the
instrument side panel; pull the cover straight off to expose the filter.
Cleaning the Condenser Block
The condenser block and/or bubbler stone may become contaminated
with mineral or other deposits, resulting in a loss of air flow through the
LI-610. A severe loss of air flow may also indicate that the air pump
diaphragm has failed. A pump that is functioning normally will generally
output a pressure of 450 to 600 mb, when measured at the TO
CONDENSER port.
If the pump appears to be functioning normally, you may need to clean
the condenser block with a solution of 1N acetic acid.
To clean the condenser block:
• Drain the condenser block assembly; it is not necessary to drain the
radiator assembly.
• Connect a new section of Bev-a-line tubing with attached female
Luer lock to the fill/drain fitting on the condenser block housing.
• Turn the air pump on and open the flow adjust valve very slightly;
just enough to prevent any acetic acid from backing up into the hose
attached to the bottom of the condenser block.
• Fill the condenser with 1N acetic acid using the syringe or small
squeeze bottle (included). Fill until the acetic acid rises in the
fill/drain tube and is approximately 1 cm below the top of the
condenser housing. Rinse the syringe and/or squeeze bottle with
5-4
Maintenance
distilled water thoroughly 4-5 times to remove any residual acetic
acid.
• Allow the acetic acid to soak in the block for about 10-15 minutes.
To drain the block, plug the output ports on the instrument front
panel, or use the syringe to draw the acid out. Turn the air pump ON,
and open the flow adjust valve slightly; the acid will drain through
the hose attached to the fill/drain fitting. CAUTION: Be sure that
the hose attached to the fill/drain fitting is directed away from your
face. Acid will squirt for a considerable distance if the air pump is
turned on with the flow adjust valve substantially open. Fill with
distilled water, drain, and repeat 4-5 times to thoroughly clean the
condenser block.
Fuses
The 6 amp fuse in the holder on the back panel protects the 10.5-16 VDC
battery circuit. The 1 amp slow-blow fuse protects the 610-01 AC
Module that is used with 100-130/200-260 VAC line voltage.
If the LI-610 fails to turn on, check the fuse for the power source you are
using (battery or AC). If the Dew Point Generator continually blows
fuses it is in need of repair.
Replacing the Air Pump Diaphragm
The air pump diaphragm may fail from pressure surges or from prolonged
operation. If the pump motor appears to be functioning normally, but the
rate of air flow is greatly reduced, it may be an indication that the
diaphragm has failed. A replacement Brailsford air pump diaphragm is
included in your spare parts kit. A pump that is functioning normally will
generally output a pressure of 450 to 600 mb, when measured directly at
the TO CONDENSER port.
Spare diaphragms can be ordered from LI-COR under part number 24703536 (1 each).
Maintenance
5-5
Section 5
To replace the diaphragm:
• Remove the LI-610 top cover.
• It is generally not necessary to remove the air hoses from the inlet
In
Out
Slotted Screws
Pump Head
and outlet ports on the pump head.
• Unscrew the four slotted screws and remove the pump head.
• Hold the connecting rod, unscrew the single flat head screw, and
remove the old diaphragm.
Dust Cover
• Place a small amount of the grease provided along the edge of the
new diaphragm.
• Move the connecting rod to the bottom of its stroke and hold it
Diaphragm
while installing the new diaphragm. The diaphragm must be
properly centered by the plastic retaining washer. Screw the flat
head screw down snug.
• Reinstall the dust cover.
Connecting
Rod
• Reinstall the pump head. Make sure that the rim of the new
diaphragm is correctly seated in the matching groove on the
underside of the pump head before tightening the four screws.
• Turn the air pump on and block the outlet port on the pump head
momentarily to form the new diaphragm.
• Reinstall the air hoses, and reassemble the LI-610 case.
5-6
Maintenance
Recharging the 6200B Battery
Make sure that the voltage selector slide switch on the back of the battery
charger is set to appropriate line voltage (115 or 230 VAC).
Plug the charger into mains power.
illuminate.
The AC indicator light will
The CHARGE indicator will illuminate if any of the batteries connected
to the charger are being charged. One method for testing a battery’s
charge is to connect it by itself into the charger. If it is charged, the
CHARGE light will come on for only a few seconds. If the CHARGE
light illuminates with no batteries connected, the AC voltage selector
switch on the back is in the wrong position.
A fully discharged 6200B battery will require about 4 hours to recharge.
Four discharged batteries connected simultaneously would require 16
hours to recharge.
Maintenance
5-7
Section VI.
Troubleshooting
This section summarizes some things that might go wrong, and suggests
what to do about these problems should they occur.
Instrument Can't
Maintain Dew Point
A dirty water filter screen can cause the LI-610 to produce a squeaking
noise every few seconds, condensation in the radiator housing, and an
inability for the instrument to maintain the chosen dew point.
See Section 5, Internal Water Filter Screen, for instructions on how to
clean the water filter screen.
Instrument Can't
Achieve Setpoint
Below Ambient
Temperature
In some cases the LI-610 may be able to achieve a temperature setpoint
above the ambient temperature, but is not able to achieve a setpoint
below ambient. This problem can be caused by a variety of problems:
1.
2.
3.
4.
Radiator and coolant reservoir are empty.
Coolant pump is off or not functioning properly.
Blockage in cooling water path.
Peltier coolers not receiving proper voltage.
First, make sure the radiator contains coolant - water should be visible in
the radiator fill tube.
Check to make sure that the coolant pump is working properly.
Disconnect the "To Cooler" line, power on the LI-610, and briefly toggle
the "COOLER" switch to the ON position. If the pump is working
properly, water will discharge from the "To Cooler" port. If water does
not discharge, contact LI-COR.
Check for a blockage in the cooling water path. Without coolant
circulating through the Peltier coolers to dissipate heat, they cannot
achieve a temperature target below ambient. There are two Peltier
coolers, one on each side of the condenser block. There are water lines
that connect the two coolers, and also run to and from the radiator. A
blockage can occur in any of the hose fittings that connect to the Peltier
coolers. To remove the blockage, disconnect either the "From Cooler" or
Troubleshooting
6-1
Section 6
"To Cooler" hoses from the back of the LI-610. Use the syringe supplied
with the LI-610 and seal it to the hose fitting as best you can. Then use
the syringe to push and pull water through the system until the water
flows freely. This should dislodge any blockage that might inhibit
coolant circulation. If a blockage is detected, flush it out of the lines.
The precipitates that cause these blockages are generally formed during
storage by a reaction between water, air, and the brass hose fittings.
These precipitates can be prevented by keeping the radiator reservoir full
of deionized water during storage (if stored in temperatures above
freezing).
If the above measures do not solve the problem, the Peltier coolers may
not be powered properly and you should contact LI-COR.
Precipitates Have
Formed and are
Blocking the Water
Lines
As mentioned above, precipitates can form within the LI-610 by a
reaction between water, air, and the brass hose fittings used to connect
the water hoses to the Peltier coolers and the condenser block. If the
cooler tubes are blocked, the condenser block can overheat in a very
short time, causing the coolers to shut down. In most cases these
precipitates form when the LI-610 is stored without water in the radiator
and condenser block assemblies, as when it is stored in freezing
conditions. When the radiator and condenser block assemblies are
drained, water droplets can adhere to the brass hose barbs on the cooling
blocks; these droplets generally can't be forced out, even under pressure
from the LI-610's air pump. Because of this, we recommend that if the
LI-610 is to be stored, and won't be exposed to freezing temperatures, it
is best to leave the system full of water.
If precipitates have formed at the bottom of the condenser block, it is
possible to thread a thin piece of wire down through the fill/drain port
and try to dislodge the deposits. If the blockage is near the Peltier
coolers, use the syringe included with the LI-610 to try to dislodge the
blockage, as described above at "Instrument Can't Achieve Setpoint
Below Ambient Temperature".
Power On Problems
6-2
Troubleshooting
Try a different battery, or if using AC power, check the AC voltage
select switch on the AC Module to make sure that it is set properly.
Check the fuses to see if one has blown.
If the voltage select switch is set improperly, the instrument may turn on,
even though the voltage is too low to activate the LO BATT circuit. The
instrument pumps will also operate, but at a greatly reduced rate.
Reduced Air Flow
Rate
If the output air flow rate diminishes over time, check the internal air
filter, and replace if necessary.
Reduced air flow rate may also be an indication that the bubbler stone in
the condenser block is corroded, or clogged with precipitates. Clean the
condenser block as described in Section 5.
A severe loss of air flow may indicate that the air pump diaphragm has
failed. See Section 5 for instructions on replacing the pump diaphragm.
A pump that is functioning normally will generally output a pressure of
450 to 600 mb, when measured at the TO CONDENSER port.
LI-610 Output "Spits"
During Operation
If the air flow rate from the LI-610 is erratic, or if water droplets appear
in the FROM CONDENSER tube during operation (i.e., the condenser
“spits”), it may be due to precipitates forming in the condenser block
water. Replace with distilled water and resume operation.
NOTE: Operation of the LI-610 in environments with high CO2
concentrations (>500 ppm) may accelerate precipitate formation with
attendant problems. Change condenser water more often under those
circumstances. It may be necessary to change water daily in extreme
cases (CO2 concentrations >1000 ppm), See Section 2 for complete
details.
Water Pump and/or
Fan Do Not Run
It is important that the output air stream is free of water drops, as the dew
point will be incorrect if this phenomenon occurs. Check the FROM
CONDENSER tube to see if water drops are present.
If the water pump and/or air fan do not operate, it may indicate that
cooler switch has failed. Contact LI-COR for service information.
Troubleshooting
6-3
Appendix A. Specifications
Dew Point Range:
Accuracy:
Stability:
Repeatability:
Response Time:
Temperature Sensor:
Display:
Display Resolution:
Noise Level:
Flow Rate:
Flow Meter Type:
Flow Meter Accuracy:
Flow Outputs:
Maximum Input Flow Rate:
Maximum Pressure Differential:
(between input & output ports)
Maximum Pressure Surge:
Analog Output:
Command Input:
Low Battery Detection:
Operating Range:
Storage Conditions:
Power Requirements:
Weight:
Size:
0 to 50 °C (limited to 35 °C below the cooling water temperature).
± 0.2 °C (0 to 50 °C).
< 0.02 °C per day at 25 °C typical; < 0.04 °C per day at 25 °C
maximum.
± 0.01 °C.
Typically 15 seconds per °C when changing from ambient to a
higher dew point; 30 seconds per °C for dew points below
ambient.
Platinum resistance-temperature-detector (RTD).
4 1/2 digit LCD for displaying Temp Set, Temp °C, or Battery
voltage.
0.01 °C.
0.01 °C (peak-to-peak).
Adjustable, to 1.7 liters per minute maximum (internal pump
capability 1.5 liters per minute).
Dwyer series RMA. 2.5 liters min-1 full scale.
± 4% of full scale reading.
Two rapid connect hose fittings for 1/8" ID by 1/4" OD plastic
tubing (adjustable at Output 2).
2 liters min-1.
140 kPa (20 psi).
35 kPa (5 psi).
0 to 5 Volts (100 output impedance), 100 mV/°C.
0 to 5 Volts, 100 mV/°C.
LED display at ~10.4 Volts (automatic shutdown at 10V).
0 to 50 °C, 0 to 95% RH (non-condensing).
0 to 55 °C (-20 to +55 °C when drained).
10.5 to 16 VDC, 5.5 amps maximum current draw; or 108126/216-252 VAC with 610-01 AC module.
8 kg (17.7 lbs.) with 6200B Rechargeable Battery; 7.86 kg (17.4
lbs.) with 610-01 AC Module.
23.5 21 28.5 cm (H W D). 9" 8.1" 11".
Specifications
A-1
Appendix B.
Saturation Vapor Pressure Table
Temp.°C
.0
.1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
0.614
0.660
0.709
0.761
0.817
0.876
0.939
1.006
1.077
1.152
1.233
1.318
1.408
1.503
1.605
1.712
1.825
1.945
2.072
2.206
2.347
2.497
2.654
2.821
2.996
3.181
0.618
0.664
0.714
0.766
0.822
0.882
0.945
1.013
1.084
1.160
1.241
1.326
1.417
1.513
1.615
1.723
1.837
1.957
2.085
2.220
2.362
2.512
2.671
2.838
3.014
3.200
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
3.376
3.580
3.796
4.023
4.262
4.513
4.776
5.053
5.344
5.649
5.969
6.305
6.657
7.025
7.412
7.816
8.239
8.683
9.146
9.631
10.137
10.666
11.219
11.796
12.399
3.396
3.602
3.818
4.046
4.286
4.538
4.803
5.082
5.374
5.680
6.002
6.339
6.693
7.063
7.451
7.858
8.283
8.728
9.193
9.680
10.189
10.720
11.276
11.855
12.461
.2
.3
.4
.5
.6
.7
.8
.9
0.623
0.669
0.719
0.772
0.828
0.888
0.952
1.020
1.092
1.168
1.249
1.335
1.427
1.523
1.626
1.734
1.849
1.970
2.098
2.234
2.377
2.528
2.687
2.855
3.032
3.219
0.627
0.674
0.724
0.777
0.834
0.894
0.958
1.027
1.099
1.176
1.258
1.344
1.436
1.533
1.636
1.745
1.860
1.982
2.111
2.248
2.391
2.543
2.703
2.872
3.051
3.238
0.632
0.679
0.729
0.783
0.840
0.901
0.965
1.034
1.107
1.184
1.266
1.353
1.445
1.543
1.647
1.756
1.872
1.995
2.125
2.262
2.406
2.559
2.720
2.890
3.069
3.258
0.636
0.684
0.734
0.788
0.846
0.907
0.972
1.041
1.114
1.192
1.275
1.362
1.455
1.553
1.657
1.768
1.884
2.008
2.138
2.276
2.421
2.575
2.737
2.907
3.087
3.277
0.641
0.689
0.740
0.794
0.852
0.913
0.979
1.048
1.122
1.200
1.283
1.371
1.465
1.563
1.668
1.779
1.896
2.020
2.151
2.290
2.436
2.590
2.753
2.925
3.106
3.296
0.646
0.694
0.745
0.800
0.858
0.920
0.985
1.055
1.129
1.208
1.292
1.380
1.474
1.574
1.679
1.790
1.908
2.033
2.165
2.304
2.451
2.606
2.770
2.943
3.124
3.316
0.650
0.699
0.750
0.805
0.864
0.926
0.992
1.062
1.137
1.216
1.300
1.389
1.484
1.584
1.690
1.802
1.921
2.046
2.179
2.318
2.466
2.622
2.787
2.960
3.143
3.336
0.655
0.704
0.756
0.811
0.870
0.932
0.999
1.070
1.145
1.224
1.309
1.399
1.494
1.594
1.701
1.814
1.933
2.059
2.192
2.333
2.482
2.638
2.804
2.978
3.162
3.356
3.416
3.623
3.841
4.070
4.311
4.564
4.831
5.110
5.404
5.712
6.035
6.374
6.729
7.101
7.491
7.899
8.327
8.774
9.241
9.730
10.241
10.775
11.333
11.915
12.523
3.436
3.644
3.863
4.093
4.336
4.590
4.858
5.139
5.434
5.743
6.068
6.409
6.765
7.139
7.531
7.941
8.370
8.819
9.289
9.780
10.293
10.830
11.390
11.974
12.585
3.456
3.665
3.886
4.117
4.361
4.617
4.885
5.168
5.464
5.775
6.101
6.443
6.802
7.178
7.571
7.983
8.414
8.865
9.337
9.830
10.346
10.885
11.447
12.034
12.647
3.477
3.687
3.908
4.141
4.386
4.643
4.913
5.197
5.495
5.807
6.135
6.479
6.839
7.216
7.612
8.025
8.459
8.912
9.386
9.881
10.399
10.940
11.505
12.094
12.710
3.497
3.709
3.931
4.165
4.411
4.669
4.941
5.226
5.525
5.839
6.168
6.514
6.876
7.255
7.652
8.068
8.503
8.958
9.434
9.932
10.452
10.995
11.562
12.155
12.773
3.518
3.730
3.954
4.189
4.436
4.696
4.969
5.255
5.556
5.871
6.202
6.549
6.913
7.294
7.693
8.110
8.548
9.005
9.483
9.983
10.505
11.051
11.621
12.215
12.836
3.539
3.752
3.977
4.213
4.461
4.722
4.997
5.285
5.587
5.904
6.236
6.585
6.950
7.333
7.734
8.153
8.592
9.052
9.532
10.034
10.559
11.107
11.679
12.276
12.900
3.559
3.774
4.000
4.237
4.487
4.749
5.025
5.314
5.618
5.936
6.270
6.621
6.988
7.372
7.775
8.196
8.637
9.099
9.581
10.085
10.612
11.163
11.737
12.337
12.964
This table gives the saturation vapor pressure of moist air in kPa, computed according to equation 3-10 (Table 3-1), at
100 kPa total pressure.
Saturation Vapor Pressure Table
B-1
Appendix C. Psychrometric Charts
Relative Humidity (%)
100 %
12
12.365
90
10
80
40%
Saturation
Vapor
Pressure
at TDP
9
Vapor Pressure (kPa)
100%
11
8
0
0
7
•
•
•
•
Vapor
Pressure
at Tair &
40% RH
70
0%
60
50
Dewpoint
Air Temp.
Temp., TDP T air
50
6
5
40
4
30
3
20
2
10
1
0
0
0
5
10
15
20
25
30
35
40
45
50
Temperature (°C)
Psychrometric Chart showing temperature, vapor pressure, and relative humidity (0 to 50 °C).
Psychrometric Charts
C-1
Appendix C
Relative Humidity (%)
100 %
5.62
90
5
80
Vapor Pressure (kPa)
4
70
60
3
50
40
2
30
20
1
10
0
0
0
5
10
15
20
25
30
35
Temperature (°C)
Psychrometric Chart showing temperature, vapor pressure, and relative humidity (0 to 35 °C).
C-2
Psychrometric Charts
Appendix D. LI-610 Calibration Traceability
The following discussion is intended for those users interested in the
traceability of the procedures used when calibrating the LI-610.
Condenser Block
The copper condenser block temperature is used to calibrate the LI-610.
The temperature of the condenser block can be measured with greater
accuracy and resolution than the dew point of the output air stream as
measured by a dew point hygrometer.
The water temperature inside the condenser block is established by the
block temperature, and air brought to saturation at the water temperature
will have a dew point equal to the water temperature. Testing has
confirmed that air leaving the LI-610 is saturated at flow rates up to 2
liters min-1, with a dew point equal to the block and water temperature.
The platinum Resistance-Temperature-Detector (RTD) mounted on the
copper condenser block is calibrated at two temperatures: 0 °C and 49.90
°C. Any slight non-linearity of the RTD is corrected electronically. A
precision thermistor is used to calibrate the condenser block at 0 °C and
49.90 °C, as it offers much greater sensitivity than the RTD.
Thermistor
The precision thermistor used to calibrate the RTD must first be
calibrated so that its resistance is known at 0 °C and 49.90 °C. An ice
bath made according to NIST procedures is used to calibrate the
thermistor at 0 °C.
With the condenser block full of water, and air flowing through it at
approximately 2 liters per minute, the LI-610 temperature display is set to
0.00 °C. The thermistor is inserted into the condenser block, and the zero
potentiometer in the LI-610 is adjusted until the resistance of the
thermistor is the same as that recorded when it was in the ice bath.
A solid copper, temperature-controlled calibration fixture, in conjunction
with a NIST-traceable 100 precision platinum RTD probe, is used to
calibrate the thermistor at 49.90 °C. A NIST-traceable 100 standard
resistance is first provided to calibrate the ohmmeter which is used to
measure the RTD probe. The probe is then checked at 0 °C, using the ice
bath described earlier. Since the output of the probe is nearly linear and
the ratio of the probe resistance at 49.90 and 0 °C is inherently very
stable, any offset in the output of the probe noted at 0 °C can be used to
correct the measurement at 49.90 °C. The calibration fixture is then set to
49.90 °C with the probe, and the resistance of the thermistor is measured
at 49.90 °C.
The thermistor is inserted into the condenser block again (filled with
water, and air flowing), and the LI-610 temperature display is set to
49.90 °C. The span potentiometer in the LI-610 is adjusted until the
thermistor resistance is the same as it was when inserted in the calibration
fixture.
Specifications
Zero Set Point
Ice Bath:
Resolution: 0.0006 °C using thermistor.
Accuracy: ± 0.02 °C.
Noise: < ± 0.0015 °C.
Repeatability: < ± 0.002 °C.
Condenser:
Resolution: 0.0006 °C using thermistor.
Accuracy: ± 0.03 °C.
Noise: < ± 0.002 °C.
Repeatability: < ± 0.003 °C.
Stability: < ± 0.01 °C.
Span Set Point
Calibration Fixture:
Resolution: 0.0007 °C using thermistor.
Accuracy: ± 0.03 °C.
Repeatability: < ± 0.01 °C.
Condenser:
Resolution: 0.0007 °C using thermistor.
Accuracy: ± 0.05 °C.
Noise: < ± 0.002 °C.
Repeatability: < ± 0.003 °C.
Stability: < ± 0.01 °C.
Warranty
Each LI-COR, inc. instrument is warranted by LI-COR, inc. to be free from defects in material and
workmanship; however, LI-COR, inc.'s sole obligation under this warranty shall be to repair or replace any
part of the instrument which LI-COR, inc.'s examination discloses to have been defective in material or
workmanship without charge and only under the following conditions, which are:
1.
2.
3.
4.
5.
6.
The defects are called to the attention of LI-COR, inc. in Lincoln, Nebraska, in writing within one year
after the shipping date of the instrument.
The instrument has not been maintained, repaired, or altered by anyone who was not approved by
LI-COR, inc.
The instrument was used in the normal, proper, and ordinary manner and has not been abused, altered,
misused, neglected, involved in and accident or damaged by act of God or other casualty.
The purchaser, whether it is a DISTRIBUTOR or direct customer of LI-COR or a DISTRIBUTOR'S
customer, packs and ships or delivers the instrument to LI-COR, inc. at LI-COR inc.'s factory in
Lincoln, Nebraska, U.S.A. within 30 days after LI-COR, inc. has received written notice of the defect.
Unless other arrangements have been made in writing, transportation to LI-COR, inc. (by air unless
otherwise authorized by LI-COR, inc.) is at customer expense.
No-charge repair parts may be sent at LI-COR, inc.'s sole discretion to the purchaser for installation by
purchaser.
LI-COR, inc.'s liability is limited to repair or replace any part of the instrument without charge if
LI-COR, inc.'s examination disclosed that part to have been defective in material or workmanship.
There are no warranties, express or implied, including but not limited to any implied warranty of
merchantability of fitness for a particular purpose on underwater cables or on expendables such as
batteries, lamps, thermocouples, and calibrations.
Other than the obligation of LI-COR, inc. expressly set forth herein, LI-COR, inc. disclaims all
warranties of merchantability or fitness for a particular purpose. The foregoing constitutes LI-COR,
inc.'s sole obligation and liability with respect to damages resulting from the use or performance of
the instrument and in no event shall LI-COR, inc. or its representatives be liable for damages beyond
the price paid for the instrument, or for direct, incidental or consequential damages.
The laws of some locations may not allow the exclusion or limitation on implied warranties or on incidental
or consequential damages, so the limitations herein may not apply directly. This warranty gives you specific
legal rights, and you may already have other rights which vary from state to state. All warranties that apply,
whether included by this contract or by law, are limited to the time period of this warranty which is a
twelve-month period commencing from the date the instrument is shipped to a user who is a customer or
eighteen months from the date of shipment to LI-COR, inc.'s authorized distributor, whichever is earlier.
This warranty supersedes all warranties for products purchased prior to June 1, 1984, unless this warranty is
later superseded.
DISTRIBUTOR or the DISTRIBUTOR'S customers may ship the instruments directly to LI-COR if they are
unable to repair the instrument themselves even though the DISTRIBUTOR has been approved for making
such repairs and has agreed with the customer to make such repairs as covered by this limited warranty.
Further information concerning this warranty may be obtained by writing or telephoning Warranty manager
at LI-COR, inc.
IMPORTANT: Please return the User Registration Card enclosed with your shipment so that we have an
accurate record of your address. Thank you.
®
LI-COR, inc. ● 4421 Superior Street ● P.O. Box 4425 ● Lincoln, Nebraska 68504 USA
Phone: 402-467-3576 ● FAX: 402-467-2819
Toll-free 1-800-447-3576 (U.S. & Canada)
envsales@licor.com
www.licor.com
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