PT100 reading fluctuating



  • Building a new machine, also with Duet3D, but this time the ethernet version.

    When heating my hotend, the temperature reading randomly jumps to 2000.0

    https://www.youtube.com/watch?v=oXZzLojnUHs

    Any idea what is going on?



  • Oh, BTW, the whole machine is standing still, so it's very unlikely do be the wiring that is faulty.


  • administrators

    Either you have a bad connection in your PT100 wiring, or your PT100 cabling is picking up interference, probably from a stepper motor cable but possibly from a heater cable. Try these tests:

    • If you send M18 to disable all stepper motors, do you still get the temperature spikes?
    • If you stop heating by setting the target temperature to a low value e.g. 0, do you still get the temperature spikes?


  • After sending M18 and with the heater off, I still get spikes.

    I connected a TP100 directly to the daughterboard and still got spikes.

    I am replacing the DuetEthernet to check if the one I have installed now have a faulty z-axis stepper motor (no power flowing), so it will be interesting to see if anything changes.

    Thank you for you continued support 🙂



  • On my Duet the PT100 reads 2000C when it is disconnected, so to me this also looks like a wiring issue. I guess swapping out the Duet will force you to redo your wiring, which may also fix the problem 🙂

    Cheers,
    Ben.



  • I am pretty sure it's not a wireing problem.

    After changing the board (the Duet Ethernet) the fluctuations are gone, but as soon as I power on the x or z or e steppers, the temp reading jumps to 2000. Sending M18 fixes the temp reading, and it returns to normal.

    Am I the only one seeing this?

    My wires are 3m (10 feet) so I guess it comes down to interference - voltages being induced into the pt100 wires, but I would expect the hardware to have some kind of filter or similar to fight that. This however seems to not be the case.

    Back to thermistors….



  • Not needed just use twisted pair cables that fixed mine when it started doing it?



  • I don't see this with about 4 feet of wiring (unless I physically disconnect the PT100 from the Duet), but I am using twisted pair ethernet cabling, as Dougal1957 suggests. I wasn't super careful about my PT100 wiring, maybe I was lucky.

    Cheers,
    Ben.


  • administrators

    The chip used on the PT100 daughter board does include filtering, however excessive interference will still cause problems. Stepper motor wires in particular generate large amounts of interference unless they are shielded twisted pair (which they normally aren't). Shielded twisted pair wiring for the PT100 cables is ideal. However, I use ordinary unshielded 4-core cable to the PT100 in my delta printer, and despite the cable running parallel to the extruder motor cable for part of the run, I don't have that issue. What you should not do is use 2 or 4 individual wires bundled with the stepper motor wiring.



  • My experience with the PT100 and wiring, it's finicky. I had to properly ground my shielded cables that run up to the hot end carriage. Once I did, then the PT100 settled down and gave nice smooth readings. It's still susceptible to interference at the small lead from the PT100 sensor to the shielded cable. So I need to ensure my PT100 wiring from the sensor to the shielded cable needs to be run specifically in order to avoid picking up interference from the other electronics on the hot end carriage.



  • @dc42:

    The chip used on the PT100 daughter board does include filtering, however excessive interference will still cause problems. Stepper motor wires in particular generate large amounts of interference unless they are shielded twisted pair (which they normally aren't). Shielded twisted pair wiring for the PT100 cables is ideal. However, I use ordinary unshielded 4-core cable to the PT100 in my delta printer, and despite the cable running parallel to the extruder motor cable for part of the run, I don't have that issue. What you should not do is use 2 or 4 individual wires bundled with the stepper motor wiring.

    When you say 4-core cable.. how do you wire it?
    Asking as E3D pt100 sensors only has 2-pin connection.

    Can the fix for this quality issue on the Thermocupler daughterboard be used on PT100 daugherboard as well?


  • administrators

    You can use either 2 or 4 wires to connect a PT100. If you use 4 wires then the resistance of the cable and any connectors you have in it won't affect the reading. See https://miscsolutions.wordpress.com/2016/06/25/more-delta-printer-upgrades-wifi-and-silence/.

    The modification used on the thermocouple daughter boards should not be applied to the PT100 boards.


Locked
 

Looks like your connection to Duet3D was lost, please wait while we try to reconnect.