M305 Thermistor Values for the Duet Maestro on the Ender 3 Pro?



  • I am installing a Maestro into an Ender 3 Pro (different from the Ender 3). The following line was generated using the RepRapFirmware Configuration Tool: M305 P0 T100000 B4138 C0 R4700 This line gives wildly inaccurate results reporting 7°C when the actual temperature is 22°C, and reporting 53°C when the actual temperature is 84°.
    I've done some guessing and checking and come up with the following values: M305 P0 T100000 B3500 C0 R2250
    Which functions better, but still not good enough. My readings now are: Actual temperature of the bed is 96.7°C when the Duet is reporting 100, and actual temperature of the bed is 69.5° when the Duet is reporting 70, and actual temperature of the bed 30.5 when the Duet is reporting 30.

    These results are good enough for the bed heater but not good enough for the hotend. The same thermistor is installed into the hotend. I have no way of measuring actual temperatures of the hot end accurately (I'm using an IR thermometer to measure the bed). This is a picture of the Thermistor if that helps.

    Given this information, can anyone venture a guess at what thermistor I actually have, and/or what are the B and R values I should be using? Thank you for your help!

    P.S. The stock control board running Marlin was working. I went to the Creality website and downloaded their Marlin source code for the Ender 3 Pro. Assuming this firmware actually goes with these thermistors, here is the Thermistor Table from Marlin.



  • @punamenon said in M305 Thermistor Values for the Ender 3 Pro?:

    R4700

    thats for a duet wifi. the duet maestro is R2200

    use this formula to calculate the restistance from the marlin table
    Oversample*4700/(1024-Oversample)

    then put the values for temperatures 25,180,240 into the configuration tool



  • This post is deleted!


  • @veti said in M305 Thermistor Values for the Ender 3 Pro?:

    thats for a duet wifi. the duet maestro is R2200

    The equation you gave me uses the 4700 value. Isn't that the same value you were just telling me is only for the WiFi and not for the Maestro? Also, Why would the value be different between the two control boards? Isn't it just the thermistor which determines these values?

    From the Marlin Table I got the following values:
    25° = 977 Oversample value
    200° = 109 Oversample value
    265° = 38 Oversample value

    After running each through the equation you gave me I get the following:
    25°=97700Ω (Note that this is not the rated 100000Ω but it is close enough I guess)
    200°=559.89Ω
    265°=181.14Ω

    When plugged into the calculator on the configurator I get the Resulting Coefficients:
    R25 = 97700 Ω
    β = 4619 K
    C = 9.743561e-8

    My resultant line is M305 P0 T97700 B4619 C9.743561e-8 R4700

    When I plug this into my config.g I'm back to getting wildly inaccurate readings (7°C when it should be reading 22°C)



  • @punamenon From the Wiki here https://duet3d.dozuki.com/Wiki/Connecting_thermistors_or_PT1000_temperature_sensors

    Quote.........

    "The R parameter is the value (in ohms) of the series resistor on the controller electronics. You do not need to specify this value unless you are using a Duet 06 or a DueX4 expansion board. If you do specify it, the correct value is:

    Duet 2 WiFi, Duet 2 Ethernet, Duex 2 and Duex 5 expansion boards, and Duet 0.8.5: 4700
    Duet 2 Maestro: 2200
    Duet 06: older boards 1000, newer boards 4700
    Duex 4 version 0.2: 1000
    Duex 4 version 0.2a: older boards 1000, newer boards 4700
    

    Edit. The correct for the Maestro seems to be 2200 and in your OP you stated that you changed it from 4700 to 2250, so that might account for why it was better but not quite right.


  • administrators

    @punamenon said in M305 Thermistor Values for the Ender 3 Pro?:

    P.S. The stock control board running Marlin was working. I went to the Creality website and downloaded their Marlin source code for the Ender 3 Pro. Assuming this firmware actually goes with these thermistors, here is the Thermistor Table from Marlin.

    I've plugged those value sinto my spreadsheet and the calculator at https://www.thinksrs.com/downloads/programs/therm calc/ntccalibrator/ntccalculator.html. To get the same readings as Marlin does when using that table, use:

    M305 P1 T98801 B4185

    Alternatively use these S-H coefficients:

    A = 0.7250586298 e-3, B = 2.151072687 e-4, C = 1.019172637 e-7

    and convert the A and B coefficients into T and B values for M305.

    I think the reason these are slightly different from the values that you got are that you should add 0.5 to each of the ADC counts in the table, to allow for the fact that the ADC rounds down.



  • @punamenon said in M305 Thermistor Values for the Ender 3 Pro?:

    The equation you gave me uses the 4700 value.

    that is correct because the marlin table is for a resistance of 4700 which is present on nearly all 8 bit boards. so to convert it you use 4700



  • @punamenon said in M305 Thermistor Values for the Ender 3 Pro?:

    M305 P0 T97700 B4619 C9.743561e-8 R4700

    again you specified R4700. that is incorrect for the duet maestro



  • @veti @dc42 @deckingman

    Thank you all for your input and help! Here is my conclusion for anyone else finding this thread and needing an answer:

    The following settings using veti's method work:
    M305 P0 T97700 B4619 C9.743561e-8 R2200
    M305 P1 T97700 B4619 C9.743561e-8 R2200

    The following settings using dc42's numbers also work:
    M305 P0 T98801 B4185 R2200
    M305 P1 T98801 B4185 R2200

    I'm guessing that anyone using run of the mill thermistors from China (purchased on ebay or aliexpress, etc) with a Duet Maestro board will find these settings to be functional. I notice little difference between the settings from dc42 and the ones from veti. They vary from each other by only about 2°C at the high end (ABS printing temperature), and they completely agreee/match at room temperature. I'm going to go with dc42's numbers as he explained he was correcting for a rounding error, so potentially more accuracy there. All of this is assuming that the original numbers from the Marlin table were accurate.

    Disclaimer: I'm measuring the bed temperature using an IR thermometer which gives varying readings +/- 1.5°C. The accuracy of the Thermometer is also questionable (+/- 2.5°C?). I have no way of accurately measuring the temperature of the hotend. To gauge this I'm manually forcing ABS Filament through the nozzle. While I haven't gotten my fingers calibrated recently, I am comparing the feel of this to the same filament going through my other printer which is properly calibrated for temperatures, and has the same size nozzle. Given these constraints, my conclusions are more of an art than a science.



  • @dc42 said in M305 Thermistor Values for the Duet Maestro on the Ender 3 Pro?:

    B4185

    I'e just installed the Duet Maestro for Ender 3 Pro and am having issues with something in the layer change corner on my calibration cube ... https://forum.duet3d.com/topic/10623/duet-maestro-upgrade-calibrations-cube-issue/7

    Besides that issue, to add to this discussion, my bed is working perfectly using M305 P0 T98801 B4185 rather than M305 P0 T100000 B4138 R4700 which I originally found on https://www.youtube.com/watch?v=HxEk7-6RriQ&t=1031s

    That said, when using either M305 P1 T98801 B4185 or M305 P1 T97700 B4619 C9.743561e-8 R2200 my hot end measured ~160C when set to 200C. I was hearing slight clicking noise from the extruder when it was retracting and perhaps because the filament wasn't hot enough. Using the oversample/temp values above, a value of 2200 rather than 4700 since I'm using a Maestro, plugging the results into the spreadsheet dc42 linked, and using those values in my gcode, M305 P1 T45731.91 B4161.08 C10.817155e-8 R2200, has resulted in the hot end measuring 177C of 200C.

    I moved my IR all over the place to get the max temp from the hot end while it was stationary. It's difficult to measure but seems correct. Hopefully I will not cause any damage with these values? Is there anyway to better measure the hot end? It doesn't matter which way the hot end wires connect +/- correct? I'm trying to understand why the temp is so far off while the bed is working perfectly.


  • administrators

    @bugsysiegals, have you seen the recently-published Ender 3 guides at https://duet3d.dozuki.com/c/Duet_2_Maestro ?

    It's not possible to measure the hot end temperature accurately using an IR thermometer because the target area is too small.


  • administrators



  • @dc42 Math has never been my strong suit. I tried to follow along with your recommendations above to no avail. I upgraded my ender 3 about a year ago to the Duet 2 Wifi. I cannot get the right settings on my heaters. I printed ABS with the stock ender 3 board (probably why it burned up). Since switching I can't get the hotend hot enough to print ABS. It is not hot enough to get a good flow rate through the nozzle. Please help!



  • be careful the ender 3 hotend has the ptfe tube down to the nozzle. printing at abs temperatures can cause the ptfe to start giving off harmful gases.



  • @tompoper you may have a temperature limit set which prevents it from getting hotter. But as veti says it's not really a good idea to print abs with the stock ender 3 hotend unless your abs will work at the lower temp range. Perhaps switching to a different filament would be best? There are some lower temp ABS out there. Or maybe petg would suffice.



  • @Veti and @Phaedrux, thanks gents. I appreciate the advice about the off gassing from the ptfe tubing at higher temps. I am aware of this issue. I have a well ventilated area in which I print. I am in the process of swapping over to a hyper cube evolution, fully enclosed with a VOC filter installed. I just have a few more prints to get through. One of the reasons I need to figure out the temp setting on the Ender 3.


Log in to reply