USB-TEMP Unexpected Output

[mdavis]

Hello, 

I purchased 8 identical type t thermocouples and connected them to the USB-TEMP. After allowing the device 30  minutes to warm up, I used instacal to configure the device and ran the automatic calibration. Next, I placed the thermocouples close together in a cup of water before recording the output.

The results were unexpected. Channels 4-7 provide inconsistent and sine wave like output. See image attached. If I swap the thermocouples between the channels, the results are the same. Channels 4-7 always behave unexpectedly and channels 0-3 look much better.

I've repeated this work several times and each time the results were the same. 

Is there anything I can do to resolve this issue and get an more stable and consistent output?

 

[JRys]

Hello,

Your data does seem to suggest that one of the two CJC sensors is responding differently to the ambient temperatures then the other, but it is still within the specification. Typically, USB-TEMP thermocouple measurements tend to have an overall accuracy of 1-2 degree C, depending on the type and the accuracy of the wire. A slight sinusoidal swing of a few tenths of a degree is nothing to be concerned about. 

Best regards,
John