problems measuring temperature with a thermistor and cfp-tc-120

[taniarox]

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

[Matthew_Williams]

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

[taniarox]

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

[taniarox]

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_Williams]

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