NI PXI-6233 Analog Input Temperature Failing

[Gus67]

Hello,

I have a NI PXI-6233 DAQ and I just hooked up a J - Type thermocouple into one of its Analog Input Channels.  I know the wiring is all right because I followed the connection diagram from the DAQ Assistant. However, the thermocouple is just sitting in a room temperature room, not attached to anything.  I measured the ambient air temperature to be 22°C and when I get the temperature from the thermocouple it varies from 12°C to 31°C.  

The CJC value is set to 25.  Other than that I don't know what to change, to help get a correct stable readout.

[Joseph_Loo]

These are couple of questions that need to be asked:

1. What vi ar you using to retrieve the temperature?

2. What voltage range is being set?

3. How is it hooked up to the unit?

4. What Labview version are you using?

5. What operating system being used?

6. Have you looked at max to see if the voltage is fluctuating as much as you say?

7. What precision in temperature are you looking at?

    Your device has an accuracy of 120 uv but a 1 deg change is about 30 uv (-.2 to .2). Remember you lost

    half your resolution since it is +/-.

8. What polarity are you measuring?

9. What kind of noise isolation are you doing?

10. Are you physically measuring the cold junction temperature or estimating? This affects the accuracy of

     your measurments?

[Joseph_Loo]

The temperature variation is F not in C. So 1 C is about 60 uv. So your measurements should be jumping around +- 2 deg minimum.

[Gus67]

I found that it's because I am not using the built in CJC source.  Is there a way to enable one for the NI PXI 6233

[Joseph_Loo]

You will need another thermocouple to keep at room temperature. This input will be used to compensate for the temperature reading. I believe NI has a vi that does the compensation.

Remember your accuracy is probably be +/- 2 deg c given your current set of equipment.