While trying to resolve some printing issues with another printer, I decided to look more closely into whether the thermistor B values we are told to plug into the M305 command (and the default ones built in to RepRapFirmware) give us accurate temperature readings. Thermistors are generally assumed to follow the Steinhart-Hart equation (see [en.wikipedia.org]) fairly well. However, thermistor manufacturers usually ignore the C term and only publish a B value, based on the resistance change between two specified temperatures. These temperatures are often quite low, e.g. 25C and 75C.

Thermistor manufacturers sometimes publish resistance tables for their thermistors, and from these we can see how the actual resistance (from the table) compares to the predicted resistance (calculated from the published B value). Alternatively, form the table we can calculate the B value needed in the M305 command to give a correct reading in RepRapFirmware at a particular temperature. I chose 220C because it is about half way between typical PLA and ABS printing temperatures. Here are the results for the Semitec 104GT-2 thermistor, as used in the E3D v6 hot end.

Published B value (temperatures not specified): 4267
Actual B value 25/220: 4388
Indicated temperature at 220C actual, using published B value: 229.4C

So this thermistor reads about 10C too high if the published B value is put in the M305 command.

Sadly, after searching the truly awful Honeywell Sensing web site, I was unable to find any data at all for the 135-104QAD-J01 thermistor used in the RRP hot end. However, the B value quoted for a related thermistor in the same range is for 25C and 85C. So the readings from that thermistor are also likely to be some way out at printing temperatures.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Very interesting, thanks for digging in to this.

As someone who has purchased and installed an e3d with the Semitec 104gt-2 and prints with mostly materials in the 230 -250 range, should i at minimum switch the B value to 4388?

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achaz
Very interesting, thanks for digging in to this.

As someone who has purchased and installed an e3d with the Semitec 104gt-2 and prints with mostly materials in the 230 -250 range, should i at minimum switch the B value to 4388?

If you want more accurate temperature readings at those temperatures, then yes. If you already know what indicated temperatures work for you, then you could leave it at 4267.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I knew what worked on the old RRP thermistor for me, but I don't know how much the indicated temps would have shifted with the new thermistor vs the old. Have only run a single test print with the e3d v6 so far. Time to make some test prints it would seem.

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dc42
Sadly, after searching the truly awful Honeywell Sensing web site, I was unable to find any data at all for the 135-104QAD-J01 thermistor used in the RRP hot end. However, the B value quoted for a related thermistor in the same range is for 25C and 85C. So the readings from that thermistor are also likely to be some way out at printing temperatures.

What about this page?
[www.digikey.de]

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Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

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Treito

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dc42
Sadly, after searching the truly awful Honeywell Sensing web site, I was unable to find any data at all for the 135-104QAD-J01 thermistor used in the RRP hot end. However, the B value quoted for a related thermistor in the same range is for 25C and 85C. So the readings from that thermistor are also likely to be some way out at printing temperatures.

What about this page?
[www.digikey.de]

Unfortunately the datasheet links from that page are the ones I already found from other Digikey sites, which are all but useless.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

David, can you provide your actual M305 P1 line for E3D v6 hotend?

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roboprint
David, can you provide your actual M305 P1 line for E3D v6 hotend?

M305 P1 T100000 B4388 R4700 H0 L0

Change R4700 to R1000 if your Duet is an older one with 1K series resistors. Change H0 to whatever you need to get the correct reading at room temperature (mine needs H30).

Edited 1 time(s). Last edit at 07/29/2015 09:21AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
M305 P1 T100000 B4388 R4700 H0 L0
Change R4700 to R1000 if your Duet is an older one with 1K series resistors. Change H0 to whatever you need to get the correct reading at room temperature (mine needs H30).

Thank you! M305 P1 T100000 B4388 R1000 H0 L0 is very close (max +2 degrees of C difference in the range from +26 to +200 C) with my termocouple from multimeter. Replikeo's duet boards coming with 1K resistors.

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roboprint
Replikeo's duet boards coming with 1K resistors.

Even the new ones? With the 5V power PCB included? Good to know...

BTT: The chinese E3D replica and the most buyable thermistors (ebay, Replikeo, Robotdigg) seems to have a B-value of 3950 at 100k.

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Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

Quote
Treito
Even the new ones? With the 5V power PCB included? Good to know... BTT: The chinese E3D replica and the most buyable thermistors (ebay, Replikeo, Robotdigg) seems to have a B-value of 3950 at 100k.

Yes, I got new Duet from Replikeo two days ago (http://forums.reprap.org/read.php?178,532636,539157#msg-539157). With 5V power PCB (LM7805C linear regulator + two ceramic capacitors). I have received 3590 thermistor (as spare part) from Replikeo too, but I have not tested it, because I use the original thermistor from original (not chinese) E3D v6.

My Duet board received two weeks ago as it was 3 weeks here in my city and has not been delivered to the customs. Did you also had a wrong bill of material for the customs? I ordered a Duet board, some thermistors, tape and so on and the customs declaration was: "Device parts". That was all including costs and shipping.
I wanted to use the thermistor for my new heated bed as it is nearly impossible to get a suitable thermistor. I only could get 100k. Before someone asks: Unfortunately I have no heated bed with integrated thermistor, but it is Version MK3 with integrated aluminium heat spreader and the thermitsor goes to the middle. You can get this bed really cheap. I was astonished.

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Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.