Cold Junction Compensation (5034-IRT4I and 5034-IRT4IXT Only)

The junction at which temperature is measured is the hot junction. The junction where the thermocouple wire interfaces with copper are the cold junction. The transition from thermocouple wire to copper typically happens at the RTB terminal.
The thermoelectric effect alters the input signal and must be compensated to measure temperatures accurately. To compensate the input signal from your module accurately, you must use cold junction compensation (CJC) to account for the increased voltage.
When using the 5034-IRT4I or 5034-IRT4IXT module with a thermocouple input type, the channel must account for the thermoelectric effect of a junction of the thermocouple field wires and the RTB. The cold junction temperature should be within the valid sensor range. You must also make sure that the configured thermocouple sensor operating range includes the RTB ambient temperature.
The 5034-IRT4I/5034-IRT4IXT module supports following modes for CJC.
  • Onboard CJC
  • RTB CJC
  • Remote Cold Junction Channel (Remote CJC)

Onboard CJC

The CJC thermistor inside the I/O module is used for Cold Junction Compensation. If your application does not require high accuracy, you can choose to opt for onboard CJC mode. You must use RTB without CJC (5034-RTB18/5034-RTB18S) in your setup if you want to use the onboard CJC.

RTB CJC

The CJC thermistor inside the RTB is used for Cold Junction Compensation. You must use one of the following RTB with CJC:
  • 5034-RTBT - Screw-type
  • 5034-RTBTS - Push-in spring type
IMPORTANT:
RTBs with CJC are not shipped with your modules. You must purchase RTBs separately and install it on your module.

Remote CJC

Another TC/RTD channel of the I/O module is used for Cold Junction Compensation. That means:
  • Thermocouple sensor is connected to a remote termination block.
  • TC+/TC- from local removable termination block is connected to the remote termination block through copper wire.
  • Remote CJ Channel's sensor (TC/RTD) is measuring the temperature in the remote termination block.
When remote CJC is used, the module verifies that the associated remote channel has a type TC (except mV) or RTD (except Ohms) and it is not configured to use remote CJC.
For more information, see the Configuration Tag Definitions and check the tag name CJChxx.Remote.

Select CJC Mode

In the Module Properties, go to CJ Channels view to select the CJC mode.
To use Remote CJC, configure Remote Cold Junction Channel in CJ Channels view.
To use RTB CJC:
  • Set the Remote Cold Junction Channel to None (default).
  • Select the Use RTB CJC checkbox.
  • Use the 5034-RTBT/5034-RTBTS in the setup.
To use onboard CJC:
  • Set the Remote Cold Junction Channel to None (default).
  • Clear the Use RTB CJC checkbox.
  • Use the 5034-RTB18/5034-RTB18S in the setup.
To disable CJC, select Disable Compensation checkbox.
IMPORTANT: When Remote Cold Junction Channel is None and Use RTB CJC checkbox is cleared, the 5034-IRT4I/5034-IRT4IXT module detects which RTB is connected. If an RTB with CJC (5034-RTBT/5034-RTBTS) is inserted, RTB CJC is used. If an RTB without CJC (5034-RTB18/5034-RTB18S) is inserted, onboard CJC is used.
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