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Problem: Picolog with TC-08 Couple Type S above 1100°C

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Problem: Picolog with TC-08 Couple Type S above 1100°C

Postby Burkamp » Thu Jul 14, 2016 7:05 am

Hello,

i'm having trouble to get my Thermocouples type S working above 1100°C on my TC-08 with Picolog.
At first i thought the Couples were broken but they work fine at 1300°C on another logger. On Picolog the Temperature will just drop strangely when it hits the 1100°C mark. Is there anything i have to regard in the software when using type s elements. For sure the channels are all set to type s. My first workaround will be to put in a Voltage/Temp table and see if that might be the problem.

thanks for answers.

Karl
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Re: Problem: Picolog with TC-08 Couple Type S above 1100°C

Postby Martyn » Thu Jul 14, 2016 1:12 pm

What are you measuring with the thermocouples, and where are they located ?
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Re: Problem: Picolog with TC-08 Couple Type S above 1100°C

Postby Burkamp » Thu Jul 14, 2016 1:37 pm

I try to measure a surface of a ceramic specimen inside an oven. Probably sometimes the thermocouple does not touch the surface properly but the couple Type S 0,5mm wire should be capable of measure it properly. With the other logger everything works fine above 1100°C so there should be no issue with measuring conditions.
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Re: Problem: Picolog with TC-08 Couple Type S above 1100°C

Postby Martyn » Thu Jul 14, 2016 2:02 pm

If the thermocouple tips are the exposed type, and they are touching the ceramic item, then the likely issue is that the ceramic is becoming conductive at this temperature and it is a potential that is different to the ground reference of the TC08. This can cause the TC08 to go outside the maximum common mode voltage of ±7.5 V

You can resolve the issue by insulating the thermocouple tips using a suitable varnish.
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Re: Problem: Picolog with TC-08 Couple Type S above 1100°C

Postby Burkamp » Fri Jul 15, 2016 9:58 am

Conductivity is propably no issue because on the exact same setup but with another datalogger temperatures above 1100 are shown in a proper way. So beside from selecting a Type S element in the software is there anything that has to be setup? For me it looks more like a software setup problem but not a physical one in our testing system.
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Re: Problem: Picolog with TC-08 Couple Type S above 1100°C

Postby Martyn » Fri Jul 15, 2016 11:10 am

The other datalogger may have a different grounding setup, or even be battery operated, so it is likely to be conductivity. We have seen this many times before and the varnish usually solves the issue.
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Re: Problem: Picolog with TC-08 Couple Type S above 1100°C

Postby Burkamp » Mon Jul 18, 2016 6:22 am

Yes the other one is battery driven. So i'll give it a try with an insulated Thermocouple. Thanks for the hint. :D
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Re: Problem: Picolog with TC-08 Couple Type S above 1100°C

Postby Burkamp » Fri Jul 22, 2016 2:26 pm

So we could isolate the source of the problem. We use an electric oven for heating, wich has a large transformer. as soon as the ovens heating is switched off, the thermocouples show the right temperature. So it's no issue with conductivity of the ceramic. When the oven heats the temperature is only ok up to 1050°C. Then it drops. So there is an issue with the interferences of the ovens transformer. Plugging the PC with the TC08 to another electric circle does not solve the problem. So it's probably the electric emission of the transformator. We now use non-shielded cables for the thermoelements. Do you think that could be a problem as the cables act as large antennas receiving the radiation of the transformer? Could shielded cables help? A Farraday cage around the TC08 does not help at all. Could shielding the whole PC help?
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Re: Problem: Picolog with TC-08 Couple Type S above 1100°C

Postby Martyn » Mon Jul 25, 2016 1:00 pm

It could well be that the cables are picking up sufficient noise to take the TC08 outside of it's common mode operating range. I would try just shielding the cables before looking at more complete solutions.
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