Thermocouple gives large incorrect reading.

[Second_Alias]

Simple setup: type T thermocouple connected to a SCXI 1320 on a SCXI 1121 with the SCXI 1000 chassis. The chassis and the module are already recognized by the computer and the PCI-MIO-16E-4 card. The test virtual channel under Data Neighborhood (which is configured for T type, Referenced Single Ended, correct channel) outputs a reading of -6.1498e+008, which is slightly wrong since the thermocouple is at room temperature. Please help me.

[RIO-Todd]

Greetings Second Alias,

I would suggest to test a voltage source initially to see if you are able to read a correct voltage. Connect a voltage source across CH+ and CH- of the 1320 (or just short CH+ and CH- and connect one of the terminals to chassis ground in order to ground a channel). Then run a test panel on the PCI-MIO-16E-4 and enter the SCXI channel string to point to the correct channel on the SCXI-1121 (see link below for help on the SCXI channel string).

Valid SCXI Channel String Arrays under LabVIEW
http://digital.ni.com/public.nsf/websearch/6FC83B7AC9ACA5788625615B00823D65?OpenDocument

If you are able to read the correct voltage, then you know you have all of the hardware correctly connected.

Next, I would make sure you have added the SCXI-1320 terminal block as an accessory to the SCXI-1121. The SCXI-1320 has a CJC sensor that is used to read thermocouples. I would test the CJC within the test panels of the PCI-MIO-16E-4 by entering the correct channel string (if the 1121 is in slot 1 the channel string for the CJC would be "ob0!sc1!md1!mtemp"...see link below for more info. on CJC channel string). At room temperature, you should read around 0.25 V from the CJC.

How Can I Address and Use Cold Junction Compensation (CJC) with SCXI Modules?
http://digital.ni.com/public.nsf/websearch/5CA3A774944DDBD8862564EB0060234B?OpenDocument

If you are reading the correct value for the CJC, then I would go back to testing the thermocouple. Make sure you are using "built-in" for the CJC within the virtual channel.

If you are still having problems, I would double check the jumpers on the SCXI-1121 to make sure they are configured correctly. Make sure the gain and filter jumper settings match the settings in MAX. Information on the jumpers can be found in the SCXI-1121 user manual.

SCXI-1121 User Manual
http://digital.ni.com/manuals.nsf/webAdvsearch/1CE36FBE36308E478625680800547C9A?OpenDocument&vid=niwc&node=132100_US

I hope this helps.

Regards,

Todd D.
NI Applications Engineer

[Second_Alias]

Thanks for your answer. The jumper settings on the 1121 were set at the factory defaults (gain of 1000) and I had the gain on MAX set at 1.
I appreciate your time.
Chris