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Frequency, what is wrong? PICO TC-08

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Frequency, what is wrong? PICO TC-08

Postby Dave01 » Tue Dec 23, 2014 11:29 am

Hallo !

We measure temperature of our furnace. We use the USB PICO TC-08 with Typ J Elements and also Typ J miniature plug.
(Typ J elements measures temperature up to 750 °C)

On the red curve you can see the thermocouple inside the furnace and on the blue curve you can see an elements placed outside, only to meausre the room temperature.

We have this problem now the second time.

Can someine help us?

Kind Regards
Dave
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Measure 1.jpg
Measure 2.jpg
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Re: Frequency, what is wrong? PICO TC-08

Postby Hitesh » Wed Dec 24, 2014 1:12 pm

Hi Dave01,

Try swapping channels 1 and 8 for 2 and 7 respectively and so on.

Are you using a laptop or desktop PC? If you are using a laptop , is it connected to the mains supply?

Is the furnace on the same earthing as the mains supply?

Regards,
Hitesh

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Re: Frequency, what is wrong? PICO TC-08

Postby Dave01 » Sat Dec 27, 2014 12:22 am

Hallo!

We could find the problem. We used a Laptop for this application. Our USB port is direct right next to the power supply. During a measurement with these frequencies we remove the power supply from the laptop and the frequencies were gone.

Do you now why this is a problem for the datalogger ?

Kind Regards
Dave
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Re: Frequency, what is wrong? PICO TC-08

Postby alan » Sun Dec 28, 2014 7:06 am

Hi,

Is the furnace an electric/arc type? If so I have come across situations where the EMF generated in the thermocouples exceeds the common mode voltage range of the TC-08. In other cases the thermocouple tips are in electrical contact with the furnance but due to the high currents flowing the ground potential of the furnace is several volts away from the mains ground your laptop PSU is picking up.

Running the laptop on batteries has "floated" the TC-08 so solved the problem for either of these situations. If you need to run the laptop off mains then can you provide some more details on the furnance type & grounding and we will do our best to advise a solution.
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Re: Frequency, what is wrong? PICO TC-08

Postby Dave01 » Fri Jan 09, 2015 10:53 pm

Thank you for your answer.

We use the furnace "Nabertherm LT/5/11/HA/P330. I made sure, that the thermocouples are not in electrical contact with the furnace or any kind of foreign body.

We also tried something: The furnace ist connnect to the electric circuit 1 and we connected the laptop to the electric curcuit 2 (so that we have different grounding). But that did not help.

Kind Regards
Dave01
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Re: Frequency, what is wrong? PICO TC-08

Postby Dave01 » Fri Jan 09, 2015 10:57 pm

Here you can see the result, if we put out the power supply from the laptop. After some time we put it in, and put it out...,in,out,in,out and so on.
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measurement.jpg
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Re: Frequency, what is wrong? PICO TC-08

Postby Hitesh » Thu Jan 15, 2015 3:50 pm

Hi Dave01,

Try earthing the laptop - there might be a screw on the back of the laptop that can be used for this purpose. Alternatively run a wire from the TC-08 USB connector shell to mains earth.

I hope this helps,
Hitesh

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