100k NTC 3950 thermistor as option

Since there are MANY 100k 3950 NTC's out off aliexpress and ebay (with the most sells of all "3d printer thermistors"), maybe it would be a good idea to take this thermistor into the options under "Temperature sensor" as "generic 100k NTC 3950"?

I found out in many forums that all of those chinese 3d prusa i3 printer kits (like hesine, zonestar....) are using this thermistors and using wrong table values.

R25℃ ;100KΩ±1%
B Value(R25/50℃):3950K 1%
Dissipation Factor(mW/℃):1.1~1.6 In still Air
Thermal Time Constant(S):10~17 In Still Air
Operating temperature range:  (-50~+260°C)
Dimension:  1.8mm Dia X4.1mm
Lead Length  :30mm

 There are many tables I found:

http://www.pibot.com/pxl/pibot-hardware/thermistor-table.txt

or this (looks like the same)

#define NUM_TEMPS_USERTHERMISTOR0 103
#define USER_THERMISTORTABLE0 {\
{1*4,938*8},{11*4,423*8},{21*4,351*8},{31*4,314*8},{41*4,290*8},{51*4,272*8},{61*4,258*8},{71*4,247*8},\
{81*4,237*8},{91*4,229*8},{101*4,221*8},{111*4,215*8},{121*4,209*8},{131*4,204*8},{141*4,199*8},{151*4,195*8},\
{161*4,190*8},{171*4,187*8},{181*4,183*8},{191*4,179*8},{201*4,176*8},{211*4,173*8},{221*4,170*8},{231*4,167*8},\
{241*4,165*8},{251*4,162*8},{261*4,160*8},{271*4,157*8},{281*4,155*8},{291*4,153*8},{301*4,150*8},{311*4,148*8},\
{321*4,146*8},{331*4,144*8},{341*4,142*8},{351*4,140*8},{361*4,139*8},{371*4,137*8},{381*4,135*8},{391*4,133*8},\
{401*4,131*8},{411*4,130*8},{421*4,128*8},{431*4,126*8},{441*4,125*8},{451*4,123*8},{461*4,122*8},{471*4,120*8},\
{481*4,119*8},{491*4,117*8},{501*4,116*8},{511*4,114*8},{521*4,113*8},{531*4,111*8},{541*4,110*8},{551*4,108*8},\
{561*4,107*8},{571*4,105*8},{581*4,104*8},{591*4,102*8},{601*4,101*8},{611*4,100*8},{621*4,98*8},{631*4,97*8},\
{641*4,95*8},{651*4,94*8},{661*4,92*8},{671*4,91*8},{681*4,90*8},{691*4,88*8},{701*4,87*8},{711*4,85*8},{721*4,84*8},\
{731*4,82*8},{741*4,81*8},{751*4,79*8},{761*4,77*8},{771*4,76*8},{781*4,74*8},{791*4,72*8},{801*4,71*8},{811*4,69*8},\
{821*4,67*8},{831*4,65*8},{841*4,63*8},{851*4,62*8},{861*4,60*8},{871*4,57*8},{881*4,55*8},{891*4,53*8},{901*4,51*8},\
{911*4,48*8},{921*4,45*8},{931*4,42*8},{941*4,39*8},{951*4,36*8},{961*4,32*8},{971*4,28*8},{981*4,23*8},{991*4,17*8},\
{1001*4,9*8},{1011*4,-1*8},{1021*4,-26*8} }



Comments

  • I have added it as type 14.
  • Thank you very much! :)

  • The table won't work for me, that's a 40C different for 260C

    Here's my experiment from the same thermostat, which I bought from Aliexpress, stated as 100k NTC 3950 too.
    The temperature is +/- 5C from true value(in my case) above 180C.
    I highly suggest using a thermocouple on multimeter to calibrate your thermostat.
    Here's my reference:
    http://reprap.org/wiki/RDB_calibrations

    The purchase link is at the bottom.

    Temperature (C), Ohm


    https://www.aliexpress.com/item/FreeShipping-Long-distance-3D-Printer-J-head-Hotend-for-1-75mm-3-0mm-E3D-Bowden-Extruder/2041826923.html?spm=a2g0s.9042311.0.0.ZDC8F3
  • NTC 3950 is just a generic curve according to a certain formula. They are normed at 25°C having 100K resistance. The further you come away from this position, the bigger the errors may come. Even for quality thermistors where they give you the formula parameters their datasheet shows a deviation.

    So yes, NTC 3950 thermistors are just a cheap solution to spare a correct datasheet for all temperatures and depending on the source they may also vary in how they react at these temperatures. In addition there are also tolerances and 5% tolerance means at 300°C an error of up to +/-15°C would be possible.
  • i have the same thermistor and repetier shows me 162 degrees at my extruder with no heating 
    i cant find any mistake 
  • Is it connected to a thermistor input or wrongly on a thermocouple input?

    What resistance does it have at room temperature. Should be around 100K (for 25°C).
  • I also have a generic NTC 3950 thermistor that is reading 200C, but thermocouple measurement inside the heater block shows only 168C. I will try it with the table values suggested by QJNero above.
  • edited October 26
    There's a simple solution for this, implemented in MarlinKimbra firmware, i hope soon a similar solution in Repetier:

    M305 - Set thermistor and ADC parameters: H[heaters] H = 0-3 Hotend, H = -1 BED, H = -2 CHAMBER, H = -3 COOLER,
     *          A[float] Thermistor resistance at 25°C, B[float] BetaK, C[float] Steinhart-Hart C coefficien, R[float] Pullup resistor value,
                L[int] ADC low offset correction, O[int] ADC high offset correction, P[int] Sensor Pin
    With "M305 B4250" now i've not over 2° of error from 190 to 250°.
    With Repetier firmware i read "210°" in the display but the nozzle is at 187!!!!!
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