type k thermocouple is giving an offset temperature reading

[anaavilas]

Hi, I have a ni usb 6218

I am trying to get 2 temperature reading, but setting CJC value of 25 is giving me an offset of ~ 40°C.

How can I set a more accurate CJC constant value?

[anaavilas]

I have a heater here, and I realize that everytime that I plug it on, the measurement gets a bit crazy.

How can I solve that?

[RTSLVU]

---

@anaavilas wrote:

I have a heater here, and I realize that everytime that I plug it on, the measurement gets a bit crazy.

How can I solve that?

---

While I have not used your exact DAC device I have done a lot of work using K type thermocouples and an Agilent DAQ/Switch unit.

Your crazy readings with power applied could be a voltage getting onto your thermocouple. I have seen simmilar issues with the Agilent unit I use. Specially when on the metal tab of HV switching MOSFETs and TC's embedded in transformer windings.

While your DAQ may be a differential input your inputs are still limited to a maximum +/- voltage in respect to earth ground.