Temperature reading fault



  • Equipment is Duetwifi, volcano hot end with 24v heater, PT 100 sensor and daughter board.
    When I start heating temperatures are reported up until 10 degrees before target then the temperature reports as a 2000Cspike and I get this. Error: Temperature reading fault on heater 1: hardware error
    This occurs at all temperature settings although if I set the target at 100C I get 3x 2000C spikes before the error appears.


  • administrators

    My guess is that the spike occurs when the hot end heater changes from being fully on to PWM. Do you have the PT100 and hot end heater wires as different conductors in a single multicore cable? If so then you need to separate them. Twisted pair is ideal but not essential.



  • @dc42:

    My guess is that the spike occurs when the hot end heater changes from being fully on to PWM. Do you have the PT100 and hot end heater wires as different conductors in a single multicore cable? If so then you need to separate them. Twisted pair is ideal but not essential.

    Thanks for the reply. The cables are in a single untwisted bundle. I was hoping to get away with it, but no maybe not. I will get some twisted pair multi core cable and rewire.


  • administrators

    FWIW the 4 wires I run to my PT100 sensor are in a single 4-core cable, which runs parallel to the hot end wires in the same bundle. The wires are not twisted pair, but as with most multicore cables, there is a gradual twist in the cable as a whole. What I suspect is key is that the PT100 wires are twisted relative to the hot end wires, so there is very little mutual inductance between them,



  • Not wishing to throw a spanner in the works but I didn't take any precautions with either of my PT100s and haven't seen any spikes. They are both wired with individual strands of 7/02 not twisted but they are then tightly bundled into nylon braid - maybe that's the key? Anyway, the hot end one is then bundled together with the heater, probe, fans and three extruders into a single flexible conduit. The bed one runs in the same cable chain as the mains heater cable for about 800mm before splitting off to the Duet but I suspect that any 50hz interference will be filtered out by the chip.



  • To test I bypassed the wiring and the problem went away. I might try disassembling my wiring harness and twisting them or I will get some multi-strand twisted pair cable. Thanks a lot for the answer dc42. BTW Impressed with the lack of over shoot on the extruder temperature. Deckingman I did mine the same as you, but it is quite a long run. Pics can be seen here http://forums.reprap.org/read.php?397,676997,page=7



  • Well I rewired pretty much the same as Dc42's and after fixing the end stop wiring error (thanks Dc42) got the firmware sorted out. However the PT100 sensor now reads 2000c all the time. So bypassed the wiring bundle and the problem goes away. The only other power going through the loom was E motor so powered down and disconnected it and the problem goes away again. So I will need to do some research on this and get some decent twisted shielded wire and rewire again.


  • administrators

    If it reads 2000C all the time then you most likely have a bad connection.



  • Not sure what happened there. Visually checked everything, checked continuity, checked resistance, checked for shorts, no problems.
    Removed heater and extruder, PT100 works. Reconnected them and PT100 still works. I had installed firmware 1.17RC3 and DWC 1.14. Oh well moving on.
    As usual awesome support dc42.



  • I am also getting 2000C problem occasionally. I'm using a usb cable from a dead mouse to connect the sensor and the PT100 board. In my case it's very strange. It only happens when it's powered by 24v supply. If I connect a usb cable to the Duet Wifi board, the second I turn off the 24v power supply the temperature reading would become normal, however the second I turn the 24v power supply back on, the temperature reading would be 2000C again.



  • Mine is running fine now and I have a fully functioning machine. I did look at best practice wiring and nearly bought a roll of 4 wire twisted pair shielded cable. I must say the DuetWifi is a huge step up from the Rumba board in my other printer.


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