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problems measuring temperature with a thermistor and cfp-tc-120
taniarox
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07-18-2007 04:41 PM
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Hi,
I am trying to measure temperature using a thermistor probe, http://www.omega.com/ppt/pptsc.asp?ref=THX-400-NPT&Nav=temd14 , and the cfp-tc-120. To do this, I am using the Temperature Measurement.vi example. When I connected the probe to pins 1 and 2, i got a constant reading of -56 which made no sense to me. I decided to connect the probe to pins 36 and 37 and changed the fieldpoint IO point to CJ temperature. I still got a reading that I did not understand, but at least I could see the reading changing when i placed heat to the probe. I am new to Labview so I'm not sure if I am going about this the right way or how to get a correct temperature measuremment. Any help would be greatly appreciated! Thanks!
-Tania
I am trying to measure temperature using a thermistor probe, http://www.omega.com/ppt/pptsc.asp?ref=THX-400-NPT&Nav=temd14 , and the cfp-tc-120. To do this, I am using the Temperature Measurement.vi example. When I connected the probe to pins 1 and 2, i got a constant reading of -56 which made no sense to me. I decided to connect the probe to pins 36 and 37 and changed the fieldpoint IO point to CJ temperature. I still got a reading that I did not understand, but at least I could see the reading changing when i placed heat to the probe. I am new to Labview so I'm not sure if I am going about this the right way or how to get a correct temperature measuremment. Any help would be greatly appreciated! Thanks!
-Tania
Matthew_William
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07-19-2007 06:03 AM
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Hi Tania. The cFP-TC-120 module is expecting a thermocouple or millivolt input, so
a thermocouple isn't going to give you a good reading.
The easiest fix is probably to switch to something like: TC-J-NPT-G-72
Check at http://www.omega.com/pptst/TC-NPT.html
The CJ input on the TC-120 reads the temperature of a sensor inside the
CB-3 connector block, usually in Kelvin.
Matt
a thermocouple isn't going to give you a good reading.
The easiest fix is probably to switch to something like: TC-J-NPT-G-72
Check at http://www.omega.com/pptst/TC-NPT.html
The CJ input on the TC-120 reads the temperature of a sensor inside the
CB-3 connector block, usually in Kelvin.
Matt
08-02-2007 10:14 AM
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thanks for the suggestion Matt. I ordered the part suggested but I am still having some problems. I am still get a reading of -56 although when i put my hand on the thermocouple, you can see the reading increasing. Should I just put it in some ice water and scale it to that? thanks for your help! -Tania
08-02-2007 10:21 AM
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Also, I am not currently using the connector block but have made my own cheap cable to connect the positive and negative leads of the thermocouple. Could this be part of my problem?
Matthew_William
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08-02-2007 12:31 PM
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The TC-120 is expecting a cold junction temperature reference so that it can properly
calculate the delta T reported by the TC sensor. There is a cold junction sensor built
into the CB-3 connector block. I expect you could duplicate the function of the CB-3 if
you can find out what sensor is built into the CB-3 and use one of those in your setup.
Probably easier to just get a CB-3, however.
Without a cold junction reference you won't get an accurate temperature measurement.
Matt
calculate the delta T reported by the TC sensor. There is a cold junction sensor built
into the CB-3 connector block. I expect you could duplicate the function of the CB-3 if
you can find out what sensor is built into the CB-3 and use one of those in your setup.
Probably easier to just get a CB-3, however.
Without a cold junction reference you won't get an accurate temperature measurement.
Matt
