When print starts, PT100 Thermistor faults to 2000C



  • Hello,
    I just finished building my 3d printer, and I ran into a problem. I have an e3d v6 volcano with a 40W heater and a PT100 thermistor. The thermistor works great when the machine is idle reading temps very accurately. When a print starts or I try to move the 3xtruder motor, the thermistor faults and requires that I restart the printer. Attached below is my config.g file. Again, the problem only exists when a print starts or some other action is done.
    Thanks,
    John Link

    0_1534091709939_config.g



  • @jlink33 As I understand it, you are saying the temperatures read correctly when the printer is idle when you start to print. If so, the usual cause is a wiring issue - usually a bad crimp or some such. With the printer at idle and temperatures reading normal, try moving the wires around to see if you can induce the fault and thus isolate the problem.



  • I have tried jostling the wires while the hotend is at temperature and no replication.



  • @jlink33 said in When print starts, PT100 Thermistor faults to 2000C:

    Hello,
    I just finished building my 3d printer, and I ran into a problem. I have an e3d v6 volcano with a 40W heater and a PT100 thermistor. The thermistor works great when the machine is idle reading temps very accurately. When a print starts or I try to move the 3xtruder motor, the thermistor faults and requires that I restart the printer. Attached below is my config.g file. Again, the problem only exists when a print starts or some other action is done.
    Thanks,
    John Link

    0_1534091709939_config.g

    Did you buy E3D's PT100 sensor, or one of these? :
    alt text

    If you got one like in the picture, the problem is that the wires are shorting to the heater block because the teflon insulation has burned off the wires inside the cartridge. You can check it by measuring resistance between the wires and the cartridge body. Anything other than infinite resistance will read intermittently as 2000C.



  • I did purchase an e3d PT100 thermistor from filastruder.



  • @jlink33 If it faults to 2000 degrees, that usually means something is open circuit. If it sometimes reads OK but when some action such as printing is performed it goes to a fault condition, I can't think of anything that would cause that other than a bad connection somewhere. Maybe someone else can....

    BTW, I think your steps per mm for the extruder are wrong. Are you using an E3d Titan? If so, the setting of 420 steps per mm is normal for a Titan with a 1.8 degree motor and 16x micro-stepping. But you've set micro-stepping to 256 times before setting the steps per mm.

    Edit. Yes indeed, the wiring fault could be inside the PT100 cartridge.



  • Link to some Photos

    I can assure you that all connections are properly shielded and soldered. The problem comes even if I am not moving any axes. If the hotel is at 210C and I move the extruder motor 5mm, the thermistor faults.



  • @jlink33 In that case, it sounds like it might be interference from the extruder motor wiring. Do the cables run parallel with each other? If so, try separating them. Oh, and don't forget what I said about your extruder steps per mm (not that that will have any bearing on the temperature issue).

    Edit. Just looked at the wiring photos and um well, not wishing to cause offence but that's not what I'd call properly shielded.



  • Just tested it a little more, when any motor is moved, the temp jumps up to 200C even the Z-motors that have no connection whatsoever. Any thoughts now?
    Also, haha on the shielding - was speaking to the heat shrink.



  • @jlink33 said in When print starts, PT100 Thermistor faults to 2000C:

    Just tested it a little more, when any motor is moved, the temp jumps up to 200C even the Z-motors that have no connection whatsoever. Any thoughts now?

    None other than what I've already said - not really my area of expertise so I'll have to leave it to others to help you out.



  • ok, thanks. Any way to reach out to @dc42 or someone else that can help?


  • Moderator

    The best way to eliminate electrical interference for a PT100 is to use a 4 wire arrangement and to twist the wires. Each lead from the cartridge can be split further into two more leads. The 4 wires then get connected to the daughterboard.

    0_1534095376993_Screenshot 2018-08-12 11.35.14.png
    https://miscsolutions.wordpress.com/2016/06/25/more-delta-printer-upgrades-wifi-and-silence/


  • administrators

    I am wondering whether there might be a short in the PT100 cartridge between the element and the casing. Can you check it with a multimeter?

    My own PT100 is connected to the Smart Effector, and from there in a separate 4-core cable to the Duet. It runs parallel to the extruder motor wires for a short distance.


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