Thermistor configuration

[Mark Rehorst]

I am rehabilitating a CubeX Duo printer that has 230K thermistors in the hot-ends.  I found a data sheet for an EPCOS 230K thermistor that had temperature/resistance values listed, so I grabbed three values (20C, 150C, and 250C) and ran the smoothieware Steinhart-Hart calculations.  I used the coefficients returned as the thermistor description in the config file.

I ran PID autotune and then set temperature to 210C and let it stabilize.  Next I shoved a K type thermocouple into the heater block and read the temperature at 200C (so actual temperature is between 197.8C and 202.2C).  When I set the heater to 100C, my thermocouple reads 96.2C (so actual temp is between 94C and 98.4C).

Maybe that's as good as it gets (the thermistor tolerance is +/- 3%, and thermocouple tolerance is +/-2.2C), and/or maybe the thermistor isn't made by EPCOS so my input values were wrong, but is there an easy way to bump the temperature by 5% so that smoothieware will set to what my thermocouple says is 210C when the GCODE says go to 210C?

[Arthur Wolf]

Actually people measuring temperatures with thermocouples into heater blocks like this most of the time will find a 5-10 degrees difference, I think it's more to do with the measuring technique than with an actual difference. Temperatures naturally varies across the heater block I think.

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[Mark Rehorst]

Yeah, that's what I figured.  I think this is a good as it gets and that's why you have to run temperature tests on different filaments to figure out what settings to use.  Thanks!

[karabas3]

I tried to calibrate unknown 100k /25C NTC thermistor
I took ultimaker style hotend heated block with the holes for thermocouple and thermistor, Ultimaker clone thermocouple/board set and connected it to arduino/ramps.
Thermistor and heater connected to smoothieboard.
I verified that arduino supplies exactly 5v as it is important for correct thermocouple reading.
Then I measured resistance on three points (25 150 240)  and applied. Testing shows that thermistor readings are 10-20C above thermocouple reading.
Then I start to change resistance values trying  to get it more close.
I finished with +-1-3C difference. But resistance value is very different.

Was
temperature_control.hotend.rt_curve          28,87500000.0,150,2700.0,240,310.0

Now

#temperature_control.hotend.thermistor        EPCOS100K        # тип термистора см http://smoothieware.org/temperaturecontrol#toc5
#temperature_control.hotend.beta             4066             # или параметр бета термистора если известен
temperature_control.hotend.rt_curve          22,100000000.0,150,5000.0,240,490.0

понедельник, 24 октября 2016 г., 21:15:08 UTC+3 пользователь Mark Rehorst написал: