cjc compensation with scxi 1102

[braxat2000]

Hi,

I've began working in labview recently and also new at NI measuring hardware, so please have patiance with me, I searched the forum and googled for a solution but could not find an answer, so I'll try to ask here, thanks in advance for any help.

I'm using labview 8.2 and SCXI 1102 with SCXI 1303 terminal block.

My goal is to read temperature using all 32 channels, and also include cjc compensation.

I currently limit my scope to two channels, and I'm able to read temperatures with them,  and I would like to use the built in CJC compensation for them.

I've found an example in the NI help section of reading the built in cjc channel, but when I try to use this value as an input to the daq thermocouple cjc value routine I have the following issue happens:

Only one channel reads temperature correctly, the second channel shows 0, and the cjc reads correctly. If I switch the SCXI 1102 off and on, I get a correct reading on both thermocouples, but now the cjc shows incorrect reading (-273 c). this can only be solved when resetting the device, which brings me back to the first problem.

My guess would be that there is a problem with working with the cjc in parallel to another channel, but I tried sequencing them, and added delay between the tasks (they are cleared after finished sampling), so there is something else I'm doing wrong.

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My questions are how to use built in cjc compensation for all 32 channels if possible,  is it possible at all to use the provided examples in the NI help?

Thanks,

Eyal.

[GarPar]

Hi braxat2000-

     There are several things to check when you are using the 1303 terminal block in conjunction with the SCXI 1102.  There is a myriad of great articles to check related to this issue, so instead of reinventing the wheel , I will refer you to this KnowledgeBase article:

How Can I Address and Use Cold Junction Compensation (CJC) with SCXI Modules?

     From reading your problem description, I would recommend making sure that the sensor type you have selected for the cjc channel is thermistor (the 1303 uses a thermistor instead of an IC sensor). 

     Are you using built-in as the cjc source?  This is another option if you are not already using it.

     I hope this helps.  Best of luck with your application!