Setting the CJC source constant for a SCC-TC02 module

[_Bryan]

I just hooked up my thermocouple calibrator to a calibrated hand held and the hand held worked fine.  I hooke up the calibrator to the TC02 module and it reads -1699C instead of -43.3C.  Strange.  What if I just read a thermocouple then adjusted the pot to match the thermocouple, then went to a few different temps to check the results?  Again, it's not the optimal method but it should work.

[Conseils]

As you say, its realy odd that the calibrator is not giving good results. I have not had a faulty module of over 50 that I must have had through my hands.

Essentially any calibration that you perform has to be the best route, but I suspect there is a problem that has yet to be uncovered. It realy sounds like there is a problem with an earth or something similar. Is your calibrator a battery powered device or mains powered?

Either way, just as a thought, check the earth on the P.C. if you have the module connected for 'ground-referenced thermocouples' perhaps this is the issue?

[_Bryan]

The calibrator I used is powered by a 9 volt battery.  The PC and the SC-2345 is going through a Tripp-Lite Isobar Ultra surge suppressor.  I do not have the ground on the TC02 module hooked up.

[Conseils]

I have seen issues with protetction units, although there is not enough data to go much further. Sometimes the protection components inside break down and 'leak' voltages onto the earth. Same can be said for P.C. power supplies. I think that a bit more information is needed to offer more precise sugestions.

Of course you could try grounding the thermocouple and see if that helps?

[McKala[DE]]

Hello Byran,

It sounds like you are having quite a time getting going with your thermocouple measurements!  What DAQ board are you using in conjunction with your SC-2345?  Are you just testing your temperature in MAX using the test panels or are you using some other program?  Have you tried to measure just a simple voltage to verify that your DAQ board is functioning properly?

You had asked in one of your previous post about what the CJC Value should be when you have the CJC source as constant.  From the Context Help in LabVIEW and Measurement and Automation Explorer (Ctrl-H) - the CJC Value is the temperature of the cold junction of the thermocouple when CJC Source is set to Constant. The temperature value uses the same units as Input Range.

I would also try Conseils' suggestion of connecting the ground the SC-TC02 to the SC-2345 ground after verifying that your DAQ board is functioning properly.

Let us know if you are still having problems!

[_Bryan]

Hello Micaela,

  What DAQ board are you using in conjunction with your SC-2345?

I am using a PCI-6221 card.

Are you just testing your temperature in MAX using the test panels or are you using some other program? 

I wrote a small VI with a DAQmx Read block that puts the data into a waveform chart.  I have also tried the test panel in MAX.

Have you tried to measure just a simple voltage to verify that your DAQ board is functioning properly?
No I have not.  This setup is maybe 2 months old at most.

You had asked in one of your previous post about what the CJC Value should be when you have the CJC source as constant.  From the Context Help in LabVIEW and Measurement and Automation Explorer (Ctrl-H) - the CJC Value is the temperature of the cold junction of the thermocouple when CJC Source is set to Constant. The temperature value uses the same units as Input Range.
How do I measure the CJC temperature on the TC02 module so I can use it as a constant?  I found a VI called Acq CJC Temperature.vi in the examples section, but it will only measure  Dev1/boardTempsensor_vs_aignd.  I think that is the temp of the PCI-6221 card and not the TC02 module.

  Am I correct in that I must use a constant CJC value insted of the built in CJC source? (Since I am using the uncompensated panelette)

I would also try Conseils' suggestion of connecting the ground the SC-TC02 to the SC-2345 ground after verifying that your DAQ board is functioning properly.
I can give it a try.  But it goes back to the question of do I need to use a constant or can I use the built in CJC source?

Bryan

[McKala[DE]]

Hi Bryan,

I would recommend extending your cold junction point to your SCC-TC02 module and then use the "Built In" setting for your CJC source.  In order to extend the cold junction to the point of measurement with an uncompensated thermocouple jack, you can purchase the T type thermocouple wire and use this wire, instead of the copper wire that comes with the unit, to connect each thermocouple jack to the input of your measurement device (SCC-TC02).

Let us know if you need more clarifying or if this does not answer your question.

[_Bryan]

Hello Micaela,

  I like that idea.  Should I use extension wire?  Or will regular type T wire work for this?

Thank you,

Bryan

[McKala[DE]]

Bryan,

It shouldn't make a difference if it's a extension wire or the regular T type wire.  The major concern is that the wire material is the same. 

[_Bryan]

Thank you for the information.  This should make life easier.

Bryan