inline_resistor: 4740 but Configuration reference - Klipper documentation doesnt list it as an (pt1000) config option, easy to think its not valid (for pt1000) as it is listed for thermistor
I would not be aware that you can connect a PT1000 to the BTT Octopus board.
Are you talking about the BTT MAX31865 V1 or V2 board?
you can connect pt1000 to any board; some just work better in terms of accuracy and or precision. Octopus uses 0.1% pull up and series resistance to get both(ish).
But my post isnt Octopus specific - I just came across the docs only showing the inline_resistor in the regular thermistor section and not the pt1000 section while it is valid in both it seems.
Although you can connect a PT1000, it hardly makes any sense IMHO. The measured voltage drop across a PT1000 is only 1/10 of the expected value. In combination with the needed ADC the result probably is questionable.
I’d guess this is the reason why there is no
inline_resistor setting for the PT1000. Though in theory you are right, the same logic could be applied as for the regular thermistors.
One is NTC the other is PTC, so at higher temps that difference becomes smaller (1/5th at 300C); reducing the pull up resistance or adding a series resistance has pretty much the same effect on the ADC resolution in terms of degrees C pr bit.
And not to mention, the parameter actually does work for PT1000, and is probably needed on Duet boards as well as Octopus (and possibly others); but the way the parameter is shown in the current documentation it appears to not be valid for PT1000 which is unfortunate imho.
I didnt intend for a discussion on the merits of PT1000; got that bit covered.
This would be a great change to submit as a GitHub pull request, perhaps including some of the caveats discussed here.