thermistor accuracy question

[Allison Andrews]

Hi, I recently picked up a j-head V8 and seem to be getting lowish hotend temperatures relative to what Marlin thinks the hotend is at.

I set the hotend thermistor to 7 in Configuration.h which is what the hotends.com page says should work for the hotend that came with the V8, and then recompiled/downloaded my firmware.

what I'm seeing:

I set the hotend temp to 210C(ABS), but if I hold the thermocouple probe from my DMM(brand new Fluke 179) against the heater block of the V8, the DMM reads only around 160-170C. with my older jhead(mk5something) it reads a hair low(10 or so degrees) but nothing like the 40-50 degree difference I'm seeing with the V8. Is it unusual to see a thermistor this far off? any other ideas what could be causing this large of a discrepancy?

*scratches head in puzzlement/consternation*

-Allie

[wolfmanjm]

there is a difference in the thermistors that Brian ships out, they have different R/C curves, and it is not always obvious the exact model # he sends. They are the same make but different models, which have different characteristics.

[Allison Andrews]

Ugh, so I get to dig through the Honeywell data sheets till I find something that works, or I manually calibrate taking data via my thermocouple?

-Allie

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[Allison Andrews]

(or just wait for my order from digikey to come in and replace the thermistor entirely I suppose.)

[wolfmanjm]

The two I know he has shipped in the past are 135-104LAG-J01 and 135-104QAD-J01 They look identical, but the R/C table is different.

On Tuesday, September 20, 2016 at 2:57:39 PM UTC-7, Allison Andrews wrote:

Ugh, so I get to dig through the Honeywell data sheets till I find something that works, or I manually calibrate taking data via my thermocouple?

-Allie

On Tue, Sep 20, 2016 at 2:36 PM, wolfmanjm <wolf...@gmail.com> wrote:

there is a difference in the thermistors that Brian ships out, they have different R/C curves, and it is not always obvious the exact model # he sends. They are the same make but different models, which have different characteristics.

On Tuesday, September 20, 2016 at 2:06:45 PM UTC-7, Allison Andrews wrote:

Hi, I recently picked up a j-head V8 and seem to be getting lowish hotend temperatures relative to what Marlin thinks the hotend is at.

I set the hotend thermistor to 7 in Configuration.h which is what the hotends.com page says should work for the hotend that came with the V8, and then recompiled/downloaded my firmware.

what I'm seeing:

I set the hotend temp to 210C(ABS), but if I hold the thermocouple probe from my DMM(brand new Fluke 179) against the heater block of the V8, the DMM reads only around 160-170C. with my older jhead(mk5something) it reads a hair low(10 or so degrees) but nothing like the 40-50 degree difference I'm seeing with the V8. Is it unusual to see a thermistor this far off? any other ideas what could be causing this large of a discrepancy?

*scratches head in puzzlement/consternation*

-Allie

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