TBX-68T temperature measurement errors

[PollardVT]

I am using a TBX-68T with a PXI 4351 card to measure the temperature of a steel plate while the plate is undergoing a TIG (electric arc) welding process. To my knowledge (and based on past experience), the device is connected properly in MAX, with the TBX-68T selected as the accessory. In MAX it also passes the tests. Using the built in CJC and specifying a K-type thermocouple at a range of +/-0.625v, MAX reports temperatures of -80C. The temperature remains nearly the same as the range is increased, but if I change the range to +/-3.75v, the temperature suddenly jumps to 100+C. I used the Measure Thermocouple (with accessory).vi that comes with the driver, and it gives me the same readings. Furthermore, when I initiate the TIG welder the card reads extremely negative (-10e9) temperatures.

What is odd, is that I have used these devices for the exact same process in the past and it generated believable results. 

How can I fix the current temperature offset problem? Could I have possibly damaged the unit? Is it possible to use the TBX-68T to reliably detect temperature in arc welding process? 

Thanks,

William

[CharlesD]

Hello,

Becasue TIG welding creates a large electrical discharge I am concerned that you may have shorted the card.  What kind of isolation did you use to ensure a separation between the TIG process and the temperature measurement? Because the error is read by both your program and MAX it must be either the temperature configuration or the card.  Could you try to conduct a simple Voltage measurement with the 4351, lets say a AA battery.  You should be able to read 1.5-1.6V.  If this works than the card should be fine, (make sure to test all channels that are failing). 

If you cannot read the proper voltage on the card, then it is possible that the card will need to be repaired. Please update us so we can help you further.

Thank you 

[PollardVT]

Thank you for your reply, Charles. I will try the AA battery test this evening. What would be the best way to isolate the equipment? I had a grounding strap attached to my target weld plate as well as the clamp from the TIG welder. I had to remove the grounding strap from the target plate because the TIG welder wouldn't work in conjunction with it. I have since moved the strap to another location. 

Side note: The original intention of the grouding strap was to prevent any electrical interference to a motor I am using that moves the target plate along a slide table.