SCXI-1102 temperature measurement with SCXI-1300 terminal block

[realwater]

I have a SCXI-1102 in a SCXI-1000 chassis with a SCXI-1300 terminal block. I connected thermocouples at Channel 1 and Channel 2 in SCXI-1300, and also connected other wires from negative connection in each channel to chasssis ground (CHSGND) for Cold-Junction Compensation. And I tried to measure ambient temperature by K-type thermocouples. In MAX, the configuration of temperature want me to determine CJC type (user value, built-in, and user supplied), so I have user value, and MAX automatically set default temperature at 25 degree cellsius. Then I test it, but temperature by thermocouples is measured constant at 25 degree cellsius because of the setting. So I changed CJC type to built-i
n, but still the temperature is higher than ambient one.
How can I measure accurate temperature? Please help me....

[Raecine Meza]

The connections you describe are correct for using a floating thermocouple with an SCXI-1100 and SCXI-1300 terminal block. However, there is confusion about CJC. Making the connection to CHSGND is not to take care of CJC. It is to provide a return path to ground so that saturation does not occur.

There is CJC sensor built into the SCXI-1300. In order to use the built-in CJC sensor with your virtual channel, you set the SCXI-1300 as the Accessory for your SCXI-1100 module. Then when you can select the Built In option for CJC in your virtual channel.

If you are using built-in CJC option, do you see the temperature raise when you apply heat to the thermocouple? If it is behaving correctly, but the temperature is always off by a fixed amount, it is possible
that the CJC sensor is damaged. You can test the CJC temperature by requesting the SCXI channel "mtemp".

[Sergio Perillo]

And how do I test this "mtemp" channel?
Thanks

[markwysong]

The VI that I posted was intended to be used without virtual channels. It was modeled after a LabVIEW example in LabVIEW\examples\daq\SCXI\SCXI1102.llb\SCXI 1102 Thermocouple.

The cold junction compensation can be read directly from a CJC sensor on your SCXI-1300 terminal block, and the channel is called cjtemp. Try the example first.

If you want to use virtual channels in MAX, is sounds like you have done it correctly. Set the thermoucouple type to K, put in the temperature range, and select the CJC type to built-in. (This assumes that in MAX you have set up the SCXI-1102 to have an accessory of SCXI-1300, so it knows that there is a CJC on that terminal block).

Mark

[Youzhang]

"I have a SCXI-1102 in a SCXI-1010 chassis with a SCXI-1300 terminal block. I connected thermocouples and worked well before (In MAX, I selected CJC type as built-in). Then we did some wire change in SCB100, which is for PXI �6030E in slot 8 of the SCXI-1010. Now the temperature in room temperature is about 80-90 °C, much higher than the true ambient one. What is wrong?