Thermistor documenation wrong, or?



  • Been working on configuring my Duet WiFi board.

    While doing so, I am setting up thermistor for my genuine E3Dv6 hotend.

    In the Duet documentation source1, it reads:

    The Semitec 104GT-2 thermistor supplied with the E3Dv6 hot end has a quoted B value of 4267, but the actual value over 25C to 220C is 4388. For greater accuracy, use a C parameter as well.

    I dug some for more information on the E3D site, where they even have a section to setup on RepRapFirmware.
    There are 2 items of interest here, where the first is the B Value:

    For firmware versions 1.16 and earlier, set the B parameter (beta value) to 4388. This value gives better accuracy at typical printing temperatures in the range 190 to 250C than the B value of 4267 quoted in the datasheet…...... For firmware versions 1.17 and later, set the B parameter to 4725

    It actually means E3D is telling us the same thing: to use 4388 as B… but only for old firmware. E3D says we should set B at 4725 when using new firmware
    .. does it mean Duets documentation on this is no longer valid?

    [h]Second thing is C and the main thing for me to post:[/h]

    For firmware versions 1.17 and later, set the B parameter to 4725 and the C parameter to 7.06e-8.

    I have tried it and C7.05e-8 does not result in an error, but is it right, or?

    edited to correct a typo, which DC42 pointed out.


  • administrators

    That section of the E3D wiki is correct. I wrote it. Which Duet documentation page is out of date?

    The parameter C7.06e-8 (with the decimal point, which you left out) is correct.



  • David,

    I was looking at this today. I think https://duet3d.com/wiki/Connecting_thermistors is the page in question. It mentions the 4388 value but doesn't mention the 1.17 firmware variation that I can see.

    Out of interest, what sort of temp difference would you expect from B4388 vs B4725 C7.06e-8? Is it significant?

    David



  • @adavidm:

    David,

    I was looking at this today. I think https://duet3d.com/wiki/Connecting_thermistors is the page in question. It mentions the 4388 value but doesn't mention the 1.17 firmware variation that I can see.

    Out of interest, what sort of temp difference would you expect from B4388 vs B4725 C7.06e-8? Is it significant?

    David

    That was sort of what I was asking (first part)

    @dc42:

    That section of the E3D wiki is correct. I wrote it. Which Duet documentation page is out of date?

    The parameter C7.06e-8 (with the decimal point, which you left out) is correct.

    Ok, so it's a thing with the e-8? just looked so odd!


  • administrators

    You can write C0.0000000706 instead but beware of using the wrong number of zeros.

    Thanks for the link to the out-of-date page, which I have now corrected.

    The improvement in accuracy is when you use the C parameter is zero at around 220C and AFAIR a few degrees at 300C and 140C.



  • @dintid:

    …...........Ok, so it's a thing with the e-8? just looked so odd!

    Scientific notation. It's another way of saying "times ten to the power of minus eight".



  • @dc42:

    You can write C0.0000000706 instead but beware of using the wrong number of zeros.

    Thanks for the link to the out-of-date page, which I have now corrected.

    The improvement in accuracy is when you use the C parameter is zero at around 220C and AFAIR a few degrees at 300C and 140C.

    Glad to be able to finally help some and not just ask questions 🙂
    I'd advice to write that the C7.06e-8 is not a typo and maybe put in what it means in your wiki page 🙂


  • administrators

    Cheers dintid I have added a quick line to the wiki page:

    https://duet3d.com/wiki/Connecting_thermistors#Connecting


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