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Thermistors giving higher temperature than expected

Posted by shimonchick 
Thermistors giving higher temperature than expected
January 30, 2019 05:13PM
So I have a ramps 1.4 board with arduino mega setup and 2 ntc3950 thermistors on both the bed and hotend.
When I wire them the temperature reading for the hotend is 35 and the bed is 10 ( at room temperature ~20).
I have tested the thermistors using a multimeter and both give values according to their resistance chart(~120k).
When I heat the hotend it heats and reaches the required temperature, but It is probably incorrect since the initial temperature is wrong.
I have set both to option 5 in the Marlin firmware.
I suspect that something is wrong with my board, but can't figure out what.
I tried hooking a potentiometer to the A14 and A15 ping of the mega board to check if it is reading correctly and it was.
However, I do not know what internal resistance I should be reading on the ramps shield pins.
Is it possible to have a leaky capacitor or something wrong with the shield itself?
How do I test if something is wrong with the ramps/mega?
I have tried PID autotune, did not change anything.
Any advice is appreciated.
Re: Thermistors giving higher temperature than expected
February 01, 2019 12:20PM
Option 5 is for Semitec 104
For your 3950 beta you must select option 11
Option 1 works too
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