EricLarsen Posted January 4, 2011 Report Share Posted January 4, 2011 I had a customer come to me with an interesting problem and was hoping somebody here has experience with a similar issue. My customer has a thermal process that has a very high temperature transient, on the order of 500 degC/second. They are using a conventional thermocouple DAQ system, in this case an SCXI thermocouple module (not sure which one). But the SCXI system has built in lowpass filters on the order of 4Hz, so they are missing the transients. Most TC signal conditioning modules have lowpass filters and I've never tried to read a TC at a higher rate. Has anybody ever tried to read a TC at 1-2 kHz with a millivolt input DAQ card? We have a TC welding system that can weld very fine gauge TCs directly to the sample which should minimize temperature lag. It seems like by using a conventional DAQ card and appropriate cold junction compensation there isn't any reason we shouldn't be able to read this fast, but are there any issues to be aware of before heading down this path? Quote Link to comment
crelf Posted January 4, 2011 Report Share Posted January 4, 2011 I don't think I've ever worked with a thermocouple that has a response that fast - the thermocouple itself has always been the limiting temporal factor... Quote Link to comment
ShaunR Posted January 5, 2011 Report Share Posted January 5, 2011 If you can use an RTD then you can use a normal DAQ card and you don't need to worry about CJC .If you have to use a thermocouple, then you can still use a DAQ, but you will ave to provide your own CJC as you already know. That's the hard part Quote Link to comment
viSci Posted January 5, 2011 Report Share Posted January 5, 2011 IR thermocouples can have response times ~10ms, check out Omega.com Quote Link to comment
EricLarsen Posted January 5, 2011 Author Report Share Posted January 5, 2011 I don't think I've ever worked with a thermocouple that has a response that fast - the thermocouple itself has always been the limiting temporal factor... Yep, that's part of what makes this an interesting problem. A back of the evelope calculation indicates that keeping the thermal mass of the TC small relative to the thermal mass of the sample could give good results. As the TC/sample ratio increases, the TC itself starts effecting the measurement. You might be able to account for in post-process analysis if you know the masses well enough. IR thermocouples can have response times ~10ms, check out Omega.com Good idea. I didn't realize they has such fast response times. That's worth looking into. Thanks! Quote Link to comment
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