PT100 reading 40C too high
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I have an e3d toolchanger with the duet 2 wifi and two of my toolheads have PT100 sensors connected to the same daughterboard. They were working great for several months and all of a sudden, one of them reads 40C higher than the other. It appears to be tracking temperature correctly comparing the two, just 40C off. Any ideas? The connectors all seem to be snug.
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@john-meacham
Sounds like a damaged PT100. Is it a brand name sensor or a random PT100?
Real PT100's have platinum wire, you can get good sensors that are tiny but they must have a rating for the temperatures you are using.when you measure resistance what are you getting at room temp?
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@john-meacham it cold just mean that you have about 16 ohms of resistance in the connections between the PT100 and the daughter board. You can test the daughter board by disconnecting the sensor cable and connecting instead the 100 ohm resistor supplied with the board.
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It's a genuine e3d one.
Hmm.. it's possible 16 ohms snuck in somewhere, I'll disassemble things and see if i can find it. The wire connections directly to the pt100 feel really fragile, I wonder if I damaged them up when doing a nozzle change.
removing the back panel of the toolchanger is kind of a pain when all the captured nuts fall off, it's about time I design a magnetic mount for it.
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@john-meacham said in PT100 reading 40C too high:
The wire connections directly to the pt100 feel really fragile,
Indeed they are. It's very easy to damage them.
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@john-meacham
Just measure the resistance at the board, that covers everything (disconnect from daughterboard first)
if it's high, then check, the sensor directly. If there is a difference then its a bad connection between the board and sensor. If the sensor is reading a higher resistance than it should and wiggling the wires makes no difference then the sensor is stuffed. -
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I would say I found the issue if this were not my working PT100. doh. I tested with a 100ohm resistor and the daughterboard seems okay, the only thing left is inside the pt100 itself which seems randomly unreliable. I may just switch them both back to thermistors, It would be nice if micro fit 3 pigtails were available at the e3d store to repair this sort of thing.
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@john-meacham another possibility is that there is current leakage between the hot end heater and the PT100. If that is the cause, then the reading may be different (more accurate) when you remove VIN power and provide USB power only.
