Thermistor ADC H&L Values on Duet

dkaustin
Prints-a-lot
Posts: 24
Joined: Fri May 09, 2014 12:39 pm

Thermistor ADC H&L Values on Duet

Postby dkaustin » Sun Mar 12, 2017 3:20 pm

I am trying to tweak in the LCD temperature readouts on my Rostock V2/Duet and have hit a wall. No changes I make to thermistor H and L values seem to have any effect. I have tried entering M304 and M305 commands from the G-code console in the Duet web interface, tried editing M304 and M305 lines in config.g, tried entering M304 and M305 commands from the console screen on the PanelDue. The machine simply ignores any changes I make.

What am I missing?

I should add that this is a Duet 0.85, dc42 firmware version 1.17RC3, and web interface version 1.14-b4.

dc42
Printmaster!
Posts: 304
Joined: Mon Mar 07, 2016 10:17 am

Re: Thermistor ADC H&L Values on Duet

Postby dc42 » Sun Mar 12, 2017 6:31 pm

I suggest you start by upgrading to firmware 1.17e. Next, if your M305 command for the hot end is not using a C parameter, use the configtool at reprapfirmware.org to find the ideal B and C parameters for your thermistor, or for E3D hot ends use the values on their wiki.

The H and L parameters are intended only to correct for gain and offset error in the ADC. The proper way to set them is to connect fixed resistors in place of the thermistor and adjust H and L to get the readings appropriate to that resistance. But if the room temperature thermistor readings are both a long way off, it's reasonable just to set H to get a more accurate room temperature reading. H and L should not need to be outside the range -40 to +40.

The Duet WiFi has automatic ADC calibration and doesn't normally require any adjustment.


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