Sudden drop-off of temperature readings.

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Smynch
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Joined: Thu May 08, 2008 2:24 pm

Sudden drop-off of temperature readings.

Post by Smynch » Thu May 08, 2008 2:34 pm

I use a grounded USB TC-08. I am using K-type thermocouples to monitor the temperatures of the surface of a bulb which outputs UV light. The bulbs are very similar to normal strip fluorescent bulbs, but the surface can get to 950 degrees C.

However during testing I can be seeing normal temperatures from 800 - 950 C when the readings will suddenly drop off to around half, where nothing in the system I am testing has changed. Strangely I can turn the bulb off and the normal temperature reading can be obtained again, before the bulb starts to cool down. This suggests that the bulb is causing some interference in the thermocouples which translates to poor results. Could this be the case? Or is there another possibility?

picojohn
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Joined: Mon Jun 11, 2007 1:10 pm

Post by picojohn » Fri May 09, 2008 2:11 pm

Hello Smynch,

From the account that you have given, the phenomenon be may be characteristic of noise type behaviour, perhaps as a result of a peak in thermal noise at the higher temperature.

If not already doing so, you may wish to try using a screened thermocouple, with the screen grounded. Try grounding the 'sending end' and 'receiving end' alternately.

Regards
John

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