Thermocouple Measurement Errors

[mmiikkee]

Hello,

I am using Labview with a PCI-6220 DAQ and a SCB-68 terminal block to measure temperatures.  I am using 7 K-type thermocouples in differential mode with the built in CJC.  My measurement range is from room temp to about 150 degrees Celsius.

Lately, this system has been malfunctioning intermittantly in between periods of working properly.  For example, if I am measuring boiling water with all 7 thermocouples, they will all read 100 degrees in LabView for a few minutes, and then some or all of the thermocouples will begin reading incorrect temperatures of up to + or - millions of degrees.  Then the readings will return to 100 degrees.

Are there any checks I can perform on this equipment, or do you have any other advice?

Thanks!

[JoeFriedchicken]

Hi mmiikkee,

That behavior sounds like failing thermocouples. If they're occasionally becoming open circuited and then drifting, you would expect to see those kinds of readings. Do you have new thermocouples to try in place of them, or a multi-meter to check their continuity?