I cannot read thermocouples on connector 1 of the PXI-6225 M-series board.

[Mark88]

I am trying to read 30 thermocouple measurements in differential mode.  I am using AI0 as the CJC.  Attached are the connections I am using.  The negative inputs are all connected directly to AI GND.

I have no problem reading  the thermocouples in Connector 0 (AI1 through AI 7).  I have connector 1 setup in the direct feed through mode (switch 1&2 right and switch 3 up).  In MAX I get a normal reading but it does not vary by heating the thermocouple.  In my actual program it is as though there is nothing connected. Any ideas as to what I may be doing wrong?

Thanks,

Mark 

[Henrik_Volkers]

Short cut?  If you short cut a Thermocouple input you will read the CJC temperature, if you card could not detect a short cut.

[Joe_S · Accepted solution]

Mark,

Thanks for posting. I believe that the issue you might be seeing is related to how the SCB-68 must be configured in direct feedthrough mode to be used with connector 1 on the PXI-6225. When the switches on the block are set for direct feedthrough, the board is not connected to the CJC. Not having a connection to a CJC on that connector could be causing this behavior.

One potential workaround you could try is to connect a temperature sensor to AI16 and follow the steps in this KB, using that channel instead of the CJC channel. Let me know if this helps!

Regards,

Joe S.

[Mark88]

I do not know what the problem was for sure.  But I think the PXI system I am using needed to be reset after I changed it to direct feed through.  I did this previously but with the power still on.  This morning I shut it off and unpluged it from the wall and now everything seems to work fine.

Thanks for your help