Lake Shore Model 325 Temperature Controller User’s Manual
8-14 Service
8.12.2.4 Resistive Input Ranges Calibration
Purpose
To determine the input offset and gain errors when the input is configured for the resistive ranges and provide offset and
gain calibration constants back to the Model 325. This step will calibrate all resistive ranges with reversing both on and
off.
Process
1. Configure the input for the resistive range to be calibrated.
2. Reset the calibration constants to their default values using the CALZ and CALG commands.
Input: A
Range: 100 Plat/250, Reversal Off
Zero Offset Command: CALZ A,2,0
Gain Command: CALG A,2,1
3. Short all four terminals, (I+, I–, V+, V–), of the input together, do not tie the terminals to ground.
4. Via the interface obtain the input reading using the CALREAD? command and record this number.
5. Program the offset calibration by negating the value read in the previous step and providing it using the CALZ
command.
Input: A
Range: 100 Plat/250, Reversal Off
CALREAD? Reading: +000.003
Calibration Command: CALZ A,2,-0.003
6. From Table 8-2 select the calibration resistor for the range being calibrated and use the DMM in 4-lead resistance
measurement mode to measure the value of the resistor to the tolerance shown.
7. Attach the calibration resistor to the Model 325 sensor input. Be sure to connect the resistor using proper 4-lead
connection techniques.
8. Via the interface obtain the input reading using the CALREAD? command and record this number.
9. Program the gain calibration by dividing the actual resistance of the calibration resistor by the value read in the
previous step and provide the result using the CALG command. Note that the gain calibration constant will always
be within 5% of 1.00000.
Input: A
Range: 100 Plat/250, Reversal Off
Measured Value of Calibration Resistor: 100.0250
CALREAD? Reading: 100.145
Constant Calculation: 100.0250 / 100.145 = 0.99880
Calibration Command: CALG A,2,0.99880
10. Send the CALSAVE command to save the constants in the EEPROM.
11. Repeat the resistive input ranges calibration for all resistive ranges with reversal on and off.
12. Repeat all of Section 8.12.2 for second input if diode/resistor.
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