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Temperature Probes look great. Question Though

 
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rvklein




Joined: 17 Jan 2011
Posts: 20



PostLink    Posted: Sat Dec 03, 2011 2:21 pm    Post subject: Temperature Probes look great. Question Though Reply with quote


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Had to set the temperature offset on one of th PIDs to 10. Do you think that's unusually high? My thought is that is the differential isn't linear it'll be off considerably at higher temperature
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crush




Joined: 28 Dec 2010
Posts: 706
Location: Telemark, Norway


PostLink    Posted: Thu Dec 08, 2011 4:04 pm    Post subject: Reply with quote

I'm no expert, but I think the PT100's are made so 0C gives a resistance of 100 ohms, within some tolerance, and the relationship between resistance and temperature is almost linear.

The data given on wikipedia for PT100 shows a change of 0.39 ohms/C for the range -30 to 0C and 0.38ohms/C for 60 to 90C, so the non-linearity is marginal.

an offset of 10 does sound unusually high, and could be an indication of a poor solder or additional resistance added by the cables (or an imbalance in resistance?), but given that the control panel is usually at a constant temperature, the solder is effectively a constant resistance rather than a variable one. (And also the changes are negligible compared to the changes in the PT100.)

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kal
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Joined: 12 Dec 2010
Posts: 11116
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Fri Dec 09, 2011 2:07 pm    Post subject: Reply with quote

That does sound high. I think mine are 1-2 or maybe 3 at most.

What probes/cables/etc?

Kal

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milldoggy




Joined: 23 Dec 2010
Posts: 569
Location: Pottstown, PA


PostLink    Posted: Sat Dec 10, 2011 3:34 am    Post subject: Reply with quote

The docs say anything over 5 is a wiring problem.
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rvklein




Joined: 17 Jan 2011
Posts: 20



PostLink    Posted: Mon Dec 12, 2011 7:12 pm    Post subject: Reply with quote

Turns out to be a bad soldering job on my part. Soldered a new female connector and all's good
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