Software sensing if thermister disconnected

Hi,
My printer was just laying down the first layer of a print today when I noticed that one of the leads to the thermister had come off. I do not know when this happened but probably sometime during that first pass. I stopped everything just as the temperature was hitting 300 so no damage. But it got me thinking that perhaps the software should monitor the thermister for a rapid change in value and stop everything if that occurred. This had not happened in my case as the printer was happily continuing on its path as the heater temperature got higher and higher. I have not yet looked at the code to see if this is possible has anyone else ?

Alan

Edited 1 time(s). Last edit at 02/14/2014 09:23AM by alanbattersby.

Good idea.

Should not be too difficult. I would suggest a safetytrap for both the extruder head as the bed, Limits of the sensor are well known for both short contact and broken contact.

Hi Alan,

what firmware version are you using? Something similar happened to me in early December, but since then the machine switches off power to the heater if there's a disconnect (where it registers absolute zero), or overheating (where the temperature indeicates >300)

Ray

The software does normally detect when the thermistor has become disconnected, and shuts the heater down. Which firmware are you using?

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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 am using 057h-dc42 have not yet swapped to a higher version.

Alan

I was using quite an old version (probably from end of last year), not sure of version as flashed the firmware yesterday, but when knocking the wire off,the heater would not turn on. Even after reconnecting it would not start heating until the DUET was reset. I only found this out after checking all the wiring back to the DUET. So certainly I can confirm the action of a disconnected thermistor under these circumstances.

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Ormerod #007 (shaken but not stirred!)