Technical data

76 34980A Service Guide
3 Calibration Procedures
Thermocouple Reference Junction 34921A (Optional)
To make a thermocouple measurement a known reference junction
temperature measurement must be made. The reference junction
temperature is measured by two solid state temperature sensors in the
input connection area on the module. The adjustments store calibration
constants used to correct the measurements from the temperature sensors.
Thermocouple measurements using an internal reference are only
supported by the 34921A module using the optional 34921T terminal
block. The isothermal block is located on, and is an integral part of,

the terminal block.
There are no adjustments for the reference junction.
Thermocouple Reference Junction Verification
1 Read “Plug- in Module Test Considerations" on page 65.
2 Connect a calibrated thermocouple to channel 21.
3 Install the module in slot 1.
4 Place the J Type calibrated thermocouple at a known temperature 
(ice bath or calibrator).
5 Select Channel 21. Configure the channel as follows: 
TEMPERATURE 
THERMOCOUPLE 
J TYPE 
INTEG 10 PLC 
INTERNAL REF 

SENS:TEMP:TRAN:TYPE TC,(@1021)
SENS:TEMP:TRAN:TC:TYPE J,(@1021)
SENS:TEMP:NPLC 10,(@1021)
SENS:TEMP:TRANS:TC:RJUN:TYPE INT,(@1021)
6
Subtract the thermocouple error from the measured temperature. 
Verify the result is within ± 1.0 °C of the known temperature (set in
step 4).
NOTE
You should perform these verification if you are using the module for
thermocouple measurements.