
Lake Shore Model 325 Temperature Controller User’s Manual
Service
8-13
8.12.2.3
Diode Input Ranges Calibration
Purpose
To determine the input offset and gain errors when the input is configured for the diode ranges and provide offset and
gain calibration constants back to the Model 325.
Process
1. Configure the input for the diode range to be calibrated.
2. Reset the calibration constants to their default values using the CALZ and CALG commands.
EXAMPLE:
Input: A
Range: GaAlAs Diode
Zero Offset Command:
CALZ A,1,0
Gain Command:
CALG A,1,1
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.
EXAMPLE:
Input: A
Range: GaAlAs Diode
CALREAD?
Reading: +0.00005
Calibration Command:
CALZ A,1,-0.00005
6. Disconnect the V+ terminal from the others and connect to the positive output of the voltage reference. Connect the
voltage reference negative output to the V–, I+, and I– terminals.
7. Set the voltage reference to provide the calibration voltage shown in Table 8-1. Using the DMM measure the voltage
to the tolerance shown in Table 8-1.
8. Via the interface obtain the input reading using the
CALREAD?
command and record this number.
9. Program the gain calibration by dividing the measured value of the reference voltage 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.
EXAMPLE:
Input: A
Range: GaAlAs Diode
Measured Value of Reference Voltage: 7.50002 VDC
CALREAD?
Reading: 7.49852
Constant Calculation: 7.50002 / 7.49852 = 1.00020
Calibration Command:
CALG A,1,1.00020
10. Send the
CALSAVE
command to save the constants in the EEPROM.
11. Perform calibration on both diode ranges.
Table 8-1. Calibration Table for Diode Ranges
Range
Voltage Reference Output
Reference Voltage Known To
Cal. Command Type Number
Silicon Diode
2.5 VDC
±0.00010 VDC
0
GaAlAs Diode
7.5 VDC
±0.00040 VDC
1
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