Solution
NI DAQmx only supports types of thermoucouples measurements supported by the NIST standard.
A possible workaround is:
- Take an analog voltage measurement from the thermocouple.
- Convert the voltage to the correct temperature value
- Set up a custom Map Ranges scale in MAX using the linked table below, and apply it to the analog input voltage task
- Apply a reverse temperature polynomial using a Code Interface Node (the polynomial coefficients are thermocouple type specific)
In order to include cold-junction compensation (CJC) it is necessary to measure the CJC temperature and convert it to a voltage for correction of the measured thermocouple voltage.
The attached Zip file contains VIs that perform the conversions for C, D, G and L thermocouple measurements, as well as the 8 other supported types. Inputs to the "Convert Thermocouple Reading III" VI include:
- Thermocouple Voltage (Volts)
- Thermocouple Type
- CJC Temperature
- Temperature Units
The output of this VI is the corrected temperature. More details on the modifications are available in the zipped README. These VIs can easily be extended to include D and G type thermocouples.