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rvklein
Joined: 17 Jan 2011 Posts: 20
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Link Posted: Sat Dec 03, 2011 2:21 pm Post subject: Temperature Probes look great. Question Though |
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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
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Link Posted: Thu Dec 08, 2011 4:04 pm Post subject: |
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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.)
_________________ ...just one more.
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kal Forum Administrator
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
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milldoggy
Joined: 23 Dec 2010 Posts: 569 Location: Pottstown, PA
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Link Posted: Sat Dec 10, 2011 3:34 am Post subject: |
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The docs say anything over 5 is a wiring problem.
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rvklein
Joined: 17 Jan 2011 Posts: 20
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Link Posted: Mon Dec 12, 2011 7:12 pm Post subject: |
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Turns out to be a bad soldering job on my part. Soldered a new female connector and all's good
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