High Tempature Hotend Thermistor
My original thermistor deteriorated, the material holding it in the 3mm brass tube turned to ash. I decided to upgrade to a high temperature one an online seller stated was compatible... then in the fine print included the small detail of having to modify your firmware... Marlin firmware has a temperature table for this device listed as thermistor 66. I copied the contents of that project's thermistor_66.h to Prusa's thermistortables.h (firmware 3.9.3 is the latest release that works with my printer) modifying the format to match the prusa style entries and converting numbers to integer values. I also modified the line defining my temperature sensor in variants/1_75mm_MK3-EINSy10a-E3Dv6full.h #define TEMP_SENSOR_0 66. The firmware mod seems to have worked but I am now getting a mintemp error that will persist even If I change the mintemp threshold to zero and uncomment #define DEBUG_DISABLE_MINTEMP in the file for my variant. performing a factory reset and selftest reports an error that the heater/Thermistor is not connected. All connections were checked and resistance value for thermistor verified as 4.4Mohm at room temp.
Is this resistance value too high? am I overlooking something?
RE: High Tempature Hotend Thermistor
If you look the questions/answers of the buyers of this thermistor, you'll find this one :
Question : Is this a ntc or ptc, what is the ohm rating and the 25c ??
Answer: Not accurate under 200 Deg C so don't rely on the 25C resistance, just use 66 as the thermocouple reference in marlin and you'll be good for 200-450C
I have no idea if that answer is correct but, if it is, then it explains why you get a min. temp error. This thermistor would be totally inaccurate measuring the room temperature when you switch on the printer.
RE: High Tempature Hotend Thermistor
Yes, it definitely could. The info screen shows a value of 0 for hotend temperature which could throw that error. I attempted to suppress with DEBUG_DISABLE_MINTEMP but the error was still being thrown.