Thermistor temperature wrong

M4ster_3

Hello Guys,

at first, i want to thank everyone for helping me in advance!
I bought a used Creality CR-10 Max with a Duet 3 Mini 5+ Ethernet - so the mod was not made by me.
Because of that my knowledge about configure a Duet ist more or less not much - still digging into it (have the printer for 2 weeks now)

For the Problem:
Yesterday i paused and aborted a print (205°C HE and 50°C HB) and quickly after that my Hotend temperature roofed to 250+ into the thermal restriction of the duet, so it seems.
Of course i turned every heating off and let the fans cool down the printer - but unfortunately the Hotend Thermistor cooled to just 118°C but was cold to the touch.
I removed the Thermistor end from the Hotend and gently touched it and the temps went to 140-145°C.
So i thought the Thermistor went bad and fetched a new one - which diddn´t get me anywhere, as the new Thermistor show excatly the same temperature.

As both Thermistors show the same behavior and about the same temps, it occures to me that neither the thermistors or the board are broken and it´s just maybe a deleted, missing, or broken config which went bad.
I also bridged the Cable and got the expected 2000°C and when disconnected -273,1°C.

Can anyone help me out on this?

RepRapFirmware for Duet 3 Mini 5+ version 3.4.5 (2022-11-30 19:41:16) running on Duet 3 Mini5plus Ethernet (standalone mode)

(And sorry for my english, i may got a bit rusted in over the years...)

achrn

@M4ster_3 what is in your config.g? Please post the whole file.

Assuming your hot end is sensor one, what do you you get if you type M308 S1 in console?

M4ster_3

@achrn
M308 S1
Sensor 1 (Hotend) type Thermistor using pin temp1, reading 139.1, last error: sensor open circuit, T:100000.0 B:4092.0 C:0.00e+0 R:2200.0 L:-1 H:-41

the sensor open circuit was because it was disconnected.

I restarted the printer and run the code again:
M308 S1
Sensor 1 (Hotend) type Thermistor using pin temp1, reading 120.6, last error: success, T:100000.0 B:4092.0 C:0.00e+0 R:2200.0 L:-1 H:-41

Edit, sorry i overviewed the config.g request, i attached it now.config.g

achrn

@M4ster_3 the config looks OK (it matches what a quick google reports Creality using as the hotend thermistor) and the result of running M308 S1 matches what you've got set in the config.g, so I don't think it's as simple as a bad config setting, or something overwriting the setting in the config.g.

You could have a look at https://docs.duet3d.com/User_manual/Connecting_hardware/Temperature_connecting_thermistors_PT1000#when-to-calibrate and try the semi-automatic calibration, which will adjust the L and H calibration factors (but I don't know enough to say that's going to help).

M4ster_3

@achrn

If i let the Thermistor connected M308 S1 H999 will output

"M308 S1 H999
Error: M308: Computed correction H-3127 is out of range. Check that you have disconnected the thermistor."

If i disconnect it and run the code again it changes to
"M308 S1 H999
Measured H correction for port "temp1" is -47"

Going forward in the calibration procedure i bridge the Connector and the temperature changed from -273.1 to 2000.

Running then the Code M308 S1 L999 gets me this
"M308 S1 L999
Measured L correction for port "temp1" is -1"

Reconnecting the Thermistor changes "nothing" its still about 100°C to hot (shows now 126°C instead of 122°C).

Later, if no one has another idea, i will open up the housing and connect a Thermistor right to the Duet Board to exclude a cabelbreak.

M4ster_3

@M4ster_3 said in Thermistor temperature wrong:

Later, if no one has another idea, i will open up the housing and connect a Thermistor right to the Duet Board to exclude a cabelbreak.

Diddn´t change anything, still got 122°C right at the board.

Leaves me with a software or hardware Problem with the Duet itself.

Edit: Just for a blind try, i updated to the 3.5.0 Beta 2 to have a look if that "resets" something - but no it doesn´t - still 12X°C

T3P3Tony

@M4ster_3 what is the resistance of the thermistor as measured using a multimeter when not plugged into the board?

Also try switching the connection and config to temp2 temporarily to see what is reported

M4ster_3

@T3P3Tony

Hi there, it measures 125-130 kiloohms, if i´m right (sorry, i´m not an electrician)
The other 5 Thermistors i got for replacement show all the same (125kohms)
Edit2: I just put the "might be broken" Thermistor and a new one on a windowsill to get better comparison and bot showed 120kohms

I saw the second Temp Port right at my direct Board testing and thought the same - but i have to get into the configuring a bit more to be sure not to break anything xD
Edit: Or ist ist just
"M308 S1 P"temp1" Y"thermistor" T100000 B4092 A"Hotend" ; configure sensor 1 as thermistor on pin temp1"
to
"M308 S1 P"temp2" Y"thermistor" T100000 B4092 A"Hotend" ; configure sensor 1 as thermistor on pin temp2"

T3P3Tony

@M4ster_3 yes thats the change to make to test it on temp2

M4ster_3

@T3P3Tony
It did the trick it now shows ~18 degrees which is plausible, so, that means the Temp1 Port is defective?

Thank you very much so far!

T3P3Tony

@M4ster_3 yes it does indicate that, glad you got it working. I would check that the extruder is grounded in some way as one cause of this could be a build up of static charge on the extruder finding its way into the temp sensing circuit.