Thermistor documenation wrong, or?

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By dintid 20 March 2017 15:15

Member · 14 comments

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 does it mean Duets documentation on this is no longer valid?

Second thing is C and the main thing for me to post:

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 C705e-8 does not result in an error, but is it right, or?


Tech Writer
MS Infrastructure Specialist inc. Cisco

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By dc42 20 March 2017 16:11

Administrator · 2,256 comments

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 Which Duet documentation page is out of date?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.


Duet WiFi hardware designer and firmware engineer
http://www.escher3d.com
https://miscsolutions.wordpress.com

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By adavidm 24 March 2017 22:35

Member · 4 comments

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