TC measurements with PXI 4351 DAQ Card

[EBlack]

(I am using version 6i of LabVIEW). I am trying to create a VI that will use a PXI 4351 Card with a TBX-68T to take 4 thermocouple continuous measurements. I am also acquiring 8 voltages with a 6030E and TBX-68 and writing them to a file. My voltage data acquisition is modeled after "Buffered Continuous Analog Input.vi" I would like to aquire voltages and temperatures in the same vi, but using different devices and accessories. (I need a higher frequency for the voltage acquisition, and more precision with the temperatures). Is there a subvi I can use to collect the temperature data in the same vi as my voltage? I don't want the thermocouple DAQ to interfere with the voltage DAQ, either.

I tried the NI435x thermocouple.vi
but I couldn't get the Built-in Cold Junction Sensor to work or figure out how to combine it with my exisiting voltage acquisition. I also got NaN for my readings, and I checked the wire connections in all the sub vi's as suggested by another solution.

Any comments would be great. Thanks in advance.

[Claudia]

EBlack,

LabVIEW 6i ships with an example called "Cont Acq&Graph Buffered.vi". Use this example with your 6030E board. The "NI435x thermocouple.vi" should work fine for your 435x board. You can combine both programs by placing the code of the "Cont Acq&Graph Buffered.vi" in the same Block Diagram than the 435x program (keep in mind that if you copy the code and paste it into another Block Diagram, it will also copy the controls, so you will need to re-arrange them afterwards in your Front Panel). Place both the AI-SCAN and the AI Read inside the While Loop and it will work for you.
It will help if you give a more detailed description of why you feel that the built-in Cold-Junction Compensation is not working. When you switch this feature ON in the 435x program,
what happens?

Claudia Lorente
Applications Engineer
National Instruments
http://www.ni.com/ask

[EBlack]

Claudia-

Thanks for the response.

Regarding the CJC- When I switch it on, the temperature readings I get are very random, roughly negative 1 degrees. (I am operating right now at room temperature, and will be using J-type TC's to measure ~43 degrees C). Also, when I use the built-in CJC, the aquisition rate seems to slow down considerably. When I use the "user specified" everything seems to be ok, including the aquisition rate.

I measured the resitance of the Thermistor on the TBX-68T and it was about 5000 Ohms, as expected.

Just to make sure: When using the TBX-68T, do I need to hard-wire a thermocouple to Channel 1/auto-zero and another to channel 0/CJC? Because I connected a TC to channel 0 right now, but I wasn't 100%
sure.

I've attached my main vi and two sub vi's that I am using for the voltage aquisition part of my project. (Note:the current measurements are just voltage measurements multiplied by the recipricol of the resistance it was measured across, ie. 10).

I would like to keep this file as is because it writes to a file exactly the way I want it to. I'd like to have the temperature aquisition with the 4351 in the same vi as the 6030E so that they both stop and start at the same time. I am just not sure how and where to log the temperature data since there will be fewer data points than the voltage data. Any suggestions? Should I write two separate files? can I somehow append them?

Thanks again. Hope to here from you soon.