
Lake Shore Model 325 Temperature Controller User’s Manual
8-16
Service
Thermocouple Input Ranges Calibration (Continued)
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: Thermo/25mV
CALREAD?
Reading: -00.0122
Calibration Command:
CALZ A,6,+0.0122
6. Connect input to standard and DMM with cable described in Section 8.12.1.
7. Set the voltage reference to provide the calibration voltage shown in Table 8-3. Using the DMM measure the voltage
to the tolerance shown in Table 8-3.
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: Thermo/25mV
Measured Value of Reference Voltage: +25.0032 mV DC
CALREAD?
Reading: +24.9867
Constant Calculation: +25.0032 / +24.9867 = 1.00066
Calibration Command:
CALG A,6,1.00066
10. Send the
CALSAVE
command to save the constants in the EEPROM.
11. Perform calibration on both thermocouple ranges.
12. Repeat for second input if thermocouple.
Table 8-3. Calibration Table for Thermocouple Ranges
Range
Voltage Reference
Output
Reference Voltage
Known to
Cal. Command
Type Number
Thermo/25mV
+25 mV DC
±0.0070 mV DC
6
Thermo/50mV
+50 mV DC
±0.0130 mV DC
7
8.12.5 Loop 2 Heater Calibration
Overview
The Model 325 has a second control loop output, which requires calibration. Zero offset and gain errors are calibrated
out by programming offset and gain constants to the instrument.
Calibration Process
8.12.5.1
Loop 2 Voltage Output Calibration
Purpose
To determine the Loop 2 output offset and gain errors and provide offset and gain calibration constants back to the
Model 325.
Process
1. Reset the calibration constants to their default values using the
CALZ
and
CALG
commands.
EXAMPLE:
Zero Offset Command:
CALZ V,1,0
Gain Command:
CALG V,1,1
2. Connect the 100 k
resistor to the loop 2 heater output. Connect the positive lead of the DMM to the Loop 2 heater
output positive terminal, the negative lead is connected to the Loop 2 output negative terminal.
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