usb 6225 thermocouple occasionally get NaN or nonsense temperature

[Jim12345678]

I'm using a USB 6225 to read a type T thermocouple with the internal reference along with 20 differential channels through a SCB-68 terminal block and LabVIEW.  Everything is usually fine.  The program runs 24/7 polling the channels about once every two minutes usually without any problems. However, every now and then the termocouple channel generates a NaN or a ridiculous number.  I read the 20 differential channels and the 1 thermocouple chanel sequentailly as two separate tasks.   Only the thermocouple channel flakes out.  I've turned off the USB hub power save options (Windows 7), but if that were the problem I would expect the differential measurements to fail too.  They don't.   Interestingly, if I poll the hardware about once every 5 seconds, I don't see  the problem.  If I poll about once every two minutes I do.  Any ideas?

[Dennis_Knutson]

You should be using one task with all channels. Are you starting and stopping the tasks? With a single task, you only start it once and stop when the program is stopped.

[RTSLVU]

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@Jim12345678 wrote:

I'm using a USB 6225 to read a type T thermocouple with the internal reference along with 20 differential channels through a SCB-68 terminal block and LabVIEW.  Everything is usually fine.  The program runs 24/7 polling the channels about once every two minutes usually without any problems. However, every now and then the termocouple channel generates a NaN or a ridiculous number.  I read the 20 differential channels and the 1 thermocouple chanel sequentailly as two separate tasks.   Only the thermocouple channel flakes out.  I've turned off the USB hub power save options (Windows 7), but if that were the problem I would expect the differential measurements to fail too.  They don't.   Interestingly, if I poll the hardware about once every 5 seconds, I don't see  the problem.  If I poll about once every two minutes I do.  Any ideas?

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This is often indicative of an intermittent thermocouple connection.

Also high frequency/voltage on the TC, like if the TC is placed on the metal tab of a transistor in a switching powersupply.