PT100-board wishlist EMI - component maybe...



  • rumors are, next iteration of PT100-board will have an update regarding EMI and channel-separation (of the 2 channels). Just stumbeled over a component that could be beneficial???:
    https://www.analog.com/en/technical-articles/low-emi-silent-switcher.html

    If I am totally wrong here, just ignore please (and tell me so I can delete this post πŸ™‚ )


  • administrators

    We've added some extra capacitors to the latest PT100 boards. They can be retrofitted to older boards.

    I was never able to recreate the problems that users reported, even when I wrapped the PT100 wires around stepper motor cables running at 2A and 24V. But when I connected a 47pF capacitor between a stepper motor output and one of the PT100 wires to simulate even closer coupling, I got the spikes in the temperature reading that users reported. The additional capacitors fix that, even when the 47p capacitor is increased to 470p.



  • @dc42

    Please do not remember me about my metal debris, that was on the board 😞 AND my loose connectors... shame on me...
    O.K. I admit, I just read an article about it in a magazin, and thought I just post it. Maybe am "interesting component" for whatever

    Will delete this post in a few hours


  • administrators

    No, please leave it - that's an interesting datasheet link and I will follow it up.



  • @dc42

    EDIT: O.K. "But when I connected a 47pF capacitor between a stepper motor output and one of the PT100 wires to simulate even closer coupling, I got the spikes in the temperature reading that users reported. The additional capacitors fix that, even when the 47p capacitor is increased to 470p." What works, works I guess... CanΒ΄t wait to add them for noobs like me πŸ™‚

    If it absorbs everything, I hope it still throws at least a "check your wiring for short"-message, because as stupd as it may sound, most of the time it boils down to it 😞 also I am happy if I cannot burn down anything with sparks wide open illuminating the printer from within - ha πŸ™‚

    -> Just interested to build up on my non-existent knowledge: Would there be any benefit of a X2Y-Layout? (I guess there is no space for it to keep it backwards compatibel...)

    EDIT2: Would moving traces as far apart as possible while keeping them symmetrical from the 2 chips to their terminals further reduce risk of influencing one sensor the other? I guess it is neglectable "in first approximation"?

    @dc42

    EDIT3: O.K. I am realising I have to "eat my own words" (or forumposts) here I guess: If you are going to install capacitors that are so good they can even filter away my bad wiring and metal-works over electornics, I will never find my errors πŸ™‚ But I guess you are just filtering enough to have it kinda working and still not so much, so that people with bad wiring will have to look after it...


  • administrators

    @lb said in PT100-board wishlist EMI - component maybe...:

    @dc42
    If it absorbs everything, I hope it still throws at least a "check your wiring for short"-message, because as stupd as it may sound, most of the time it boils down to it 😞 also I am happy if I cannot burn down anything with sparks wide open illuminating the printer from within - ha πŸ™‚

    It will only absorb short transients.

    -> Just interested to build up on my non-existent knowledge: Would there be any benefit of a X2Y-Layout? (I guess there is no space for it to keep it backwards compatibel...)

    EDIT2: Would moving traces as far apart as possible while keeping them symmetrical from the 2 chips to their terminals further reduce risk of influencing one sensor the other? I guess it is neglectable "in first approximation"?

    EDIT3: O.K. I am realising I have to "eat my own words" (or forumposts) here I guess: If you are going to install capacitors that are so good they can even filter away my bad wiring and metal-works over electornics, I will never find my errors πŸ™‚ But I guess you are just filtering enough to have it kinda working and still not so much, so that people with bad wiring will have to look after it...

    The problem isn't trace separation on the PCB. The problem is I believe capacitive coupling between the wires from the daughter board to the PT100 and other wires that carry rapidly-changing signals, for example stepper motor cables. Also, if there isn't a connection between PSU negative output and mains ground, but there is a connection between mains ground and the printer frame (perhaps via the PSU casing), then capacitive coupling between the PT100 wires and the frame or hot end metalwork might also cause the problem.



  • @dc42 said in PT100-board wishlist EMI - component maybe...:

    @lb said in PT100-board wishlist EMI - component maybe...:

    @dc42
    If it absorbs everything, I hope it still throws at least a "check your wiring for short"-message, because as stupd as it may sound, most of the time it boils down to it 😞 also I am happy if I cannot burn down anything with sparks wide open illuminating the printer from within - ha πŸ™‚

    It will only absorb short transients.

    Is that already on the PT100-1.1-Version or from a new version on? (And will duet3 use also this daughterboard-eco-system?)

    -> Just interested to build up on my non-existent knowledge: Would there be any benefit of a X2Y-Layout? (I guess there is no space for it to keep it backwards compatibel...)

    EDIT2: Would moving traces as far apart as possible while keeping them symmetrical from the 2 chips to their terminals further reduce risk of influencing one sensor the other? I guess it is neglectable "in first approximation"?

    EDIT3: O.K. I am realising I have to "eat my own words" (or forumposts) here I guess: If you are going to install capacitors that are so good they can even filter away my bad wiring and metal-works over electornics, I will never find my errors πŸ™‚ But I guess you are just filtering enough to have it kinda working and still not so much, so that people with bad wiring will have to look after it...

    The problem isn't trace separation on the PCB. The problem is I believe capacitive coupling between the wires from the daughter board to the PT100 and other wires that carry rapidly-changing signals, for example stepper motor cables. Also, if there isn't a connection between PSU negative output and mains ground, but there is a connection between mains ground and the printer frame (perhaps via the PSU caing), then capacitive coupling between the PT100 wires and the frame or hot end metalwork might also cause the problem.

    Thanks, helps me learning. The described scenario could be my problem with all the metal used for my buildup...


  • administrators

    @lb said in PT100-board wishlist EMI - component maybe...:

    Is that already on the PT100-1.1-Version or from a new version on? (And will duet3 use also this daughterboard-eco-system?)

    The PT100 PCB revision 1.1a has the pads for the extra capacitors, however they were not fitted in the first production run using that PCB because we hadn't completed tests with the new capacitors fitted.

    The prototype Duet 3 main and expansion boards support the same PT100 and thermocouple daughter boards, and that's unlikely to change for production.


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