According to ICP-DAS USA support, the following should answer your questions:
A. Setting CJC offset
The CJC offset is set to zero at the factory. It is recommended to set the CJC offset after the module has been installed in its final location. Best performance of the module is obtained in a well-stirred and stable environment. Following is the recommended procedure to set the CJC offset using a thermocouple calibrator or ice bath.
1. Connect a thermocouple calibrator or thermocouple immersed in an ice bath* to channel 0 of the module. Be sure to use thermocouple alloy or extension grade wire for this connection, not copper wire.
2. Warm up the module for 30 minutes.
3. Run the DCON utility version 4.3.9 or later that can be downloaded from the ICP DAS website
http://www.icpdas.com.
4. Adjust the CJC offset up or down until the indicated temperature of channel 0 matches that of the thermocouple calibrator or ice bath.
* Ice baths should be well insulated, such as a Dewar bottle. Thermocouples in ice baths should read 0C. Some thermocouple ranges only go a few degrees below 0C. If you encounter problems with the module showing out of range with ice baths, please use a thermocouple calibrator instead.
B. Setting CJC offset (theoretical approach)
The CJC offset is set to zero at the factory. It is recommended to set the CJC offset after the module has been installed in its final location. Best performance of the module is obtained in a well-stirred and stable environment. Following is the recommended procedure to set the CJC offset using a thermocouple calibrator.
1. Connect the thermocouple calibrator to the analog input of the module. Be sure to use thermocouple alloy or extension grade wire for this connection, not copper wire.
2. Warm up the module for 30 minutes.
3. Set CJC offset to zero by sending the $AA9+0000 command.
4. Adjust the temperature setting of the thermocouple calibrator until the temperature reported by the module is the same as the cold junction temperature reported by the module. The temperature reported by the module can be read by sending the #AA command. The cold junction temperature reported by the module can be read by sending the $AA3 command. You can also use the DCON utility version 4.3.5 or later that can be downloaded from the ICP DAS website
http://www.icpdas.com to ease the procedure.
5. The CJC offset should be set to [(thermocouple calibrator temperature) ? (cold junction temperature reported by the module)] by using the $AA9SNNNN command.
