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Unstable temperatures with RTD sensor

Posted by rq3 
Unstable temperatures with RTD sensor
November 29, 2021 05:51PM
My printer use a 100K thermistor to sense the hot end temperature, and works very well. Plotting the temperature with Repetier Host shows the readings bounce a fraction of a degree.

However, if I install a PT1000 sensor, and recompile with a hot end sensor of 1047, the temperature plot bounces up to +/- 20 degrees, and the temperature will not stabilize enough for the print to start. No amount of PID tuning helps in any way.

I have even replaced the platinum RTD with a laboratory grade fixed resistor. The temperature reading is correct, but very unstable. Obviously Marlin does something very different when reading a thermistor versus an RTD, and not in a good way. This seems to be true for any release of Marlin.

Any thoughts would be greatly appreciated!

Edited 1 time(s). Last edit at 11/29/2021 05:52PM by rq3.
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