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USB TC-08 w/Type B thermocple

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USB TC-08 w/Type B thermocple

Postby saberry0530 » Fri Jun 01, 2007 7:01 pm

Device had qty. 6 type S TC attached and worked fine at 1300C. Had to go to 1600C , so we switched to Type B TC's. Now the TC-08 tracks temps up 1100C. It then will not read and slowly drifts down to about 400C. Everything is good up till that point. Can unplug and reset while still hiot and will not function. Let TC cool down to room temp and everything works fine, unitl you hit 1100C again. any ideas????

Thanks!!

Scott
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Postby ziko » Mon Jun 04, 2007 3:57 pm

Hi and thank you for your post. A number of factors to take into account:

1)The TC08 needs to be at a temperature of 20-30 degC to give the quoted accuracies.
2)Ensure that the thermocouples are not touching anything or getting interference that can cause some a common mode voltage
3) Try Grounding the device separately or if you are using a laptop disconnect the power adapter.

Let me know how you get on.

Kind regards
Ziko

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Postby saberry0530 » Thu Jul 19, 2007 3:06 pm

Ziko,
Have isolated the problem that when the kiln runs up to approx 15 amps, the monitored temps randomly drift around the correct temp. If I remove the power source temporarily, the temps are rock solid. Is there a way to increase the Common Node voltage rejection of the induced EMF from the heating elements? The heating elements are approx 3", 5", 7" ..... all the way up to 13" from the thermocouples. Have tried 4 computers, 3 usb cables, 3 sets of thermocouples. Am I going to have to Build a Farady cage around the heating element straps to isolate this EMF???? Or is there something that I can do to the TC-08? Thanks
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Postby ziko » Fri Jul 20, 2007 10:52 am

Hi

You could try and see whether the unit is picking up the interference or the thermocouple leads. (E.g. run the oven up to temp that causes problems, with unit in normal position but leads not in the oven – are the readings affected?) If the unit, it could be placed in a grounded metal box. Screened thermocouple leads are available, but not easily connected to ground at the TC-08 end.

An extreme possibility would be to put the TC-08 in a grounded metal box, and use screened TC leads connected to the grounded metal box.

Ultimately the TC-08 is not rated for such extreme EMI prone applications.

Hope this helps.
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Postby saberry0530 » Fri Jul 20, 2007 4:43 pm

Thanks Ziko, thats what I am leaning heavily to is putting a grounded fine screen cage around the TC's. I contacted the manufac of the kiln and they have never seen this, but then again , they use a hardware mounted TC monitoring that is not recordable. Thanks for your reply.

Scott
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Postby jb » Wed Jul 02, 2008 10:05 pm

ziko wrote:Hi

You could try and see whether the unit is picking up the interference or the thermocouple leads. (E.g. run the oven up to temp that causes problems, with unit in normal position but leads not in the oven – are the readings affected?) If the unit, it could be placed in a grounded metal box. Screened thermocouple leads are available, but not easily connected to ground at the TC-08 end.

An extreme possibility would be to put the TC-08 in a grounded metal box, and use screened TC leads connected to the grounded metal box.

Ultimately the TC-08 is not rated for such extreme EMI prone applications.

Hope this helps.


I have exactly the same problem (Induction furnace going to 1600C). At a certain power level, the readings start to go downwards and at even higher settings the readings are garbage.

I would like to know where I can get the shielded type B thermocouple wire that you refer the previous poster to. I cannot find anything that is shielded and can take 1600 C.

Also, if the TC-08 cannot take RF interference from furnaces, do you make a product that can reject that noise?

Thank you.
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Postby saberry0530 » Thu Jul 03, 2008 12:15 pm

JB,
THe only way that I finally solved my problem was to attach a capacitor to the positive leg on the output of each thermocouple to ground. I used Al caps which take the heat fairly well. about 50 Micro F 100 wvac seemed to do the trick. Good luck with yours.

Scott
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Postby jb » Thu Jul 03, 2008 2:30 pm

saberry0530 wrote:JB,
THe only way that I finally solved my problem was to attach a capacitor to the positive leg on the output of each thermocouple to ground. I used Al caps which take the heat fairly well. about 50 Micro F 100 wvac seemed to do the trick. Good luck with yours.

Scott


Thank you very much for the info. I will try that. I am curious, though, what you used as ground. Did you use the ground from the AC outlet, or the shield connection of the USB wire.

Thanks again

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Postby saberry0530 » Thu Jul 03, 2008 3:00 pm

Used Chassis ground on the furnace itself. Seemed to be the only place that would work..
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