Accuracy of Vin reading (Duet gen 3)



  • I have a 24V supply and Duet gen 3 main board. DWC is showing Vin as 23.7, my multi meter is showing exactly 24.0. They are pretty close but I'll need to crank up the voltage a bit to suit my forthcoming DC UPS. So I'd like to use the most accurate reading. The question is, which one should I believe? I'm inclined to go with the multimeter but it's quite old so might not be the best.

    On a related topic, can the Vin as displayed by DWC be adjusted along the same lines that MCU temperature can be adjusted using M912? Can't see anything in the Wiki but I might have missed it.

    tia


  • administrators

    If the multimeter is a good one, go with the multimeter.

    There is no facility to calibrate the VIN reading. It should be accurate to within +/- 3%.



  • @dc42 Thanks - I'll go with multimeter. +_ 3% of 24V approx +_0.7V so quite a wide tolerance.



  • @deckingman BTW I see the same behavior here. I haven't checked the PSU recently but I also have not adjusted anything and the last time I checked it was set to straight 24V but Duet 3 Vin will read 23.7-23.8V.



  • For 14AWG wire with 0.5m length at 16A the voltage drop is 0.13V, so you could improve with add wire between sense voltage pin of the power supply and the VIN input of the board.
    The sense pin are available on Meanwell psu.

    See https://www.calculator.net/voltage-drop-calculator.html



  • @pipersw Yes, but this is already observable in an unloaded state where the current is way below 1A at 24V. And even with 10m wire and 0.5A (still probably too much) the voltage drop would only be 0.083V.

    But it's not a problem in itself as long as it's known to be due to an inaccuracy of the measuring circuit.



  • I have add the sense wire, and I have 24.07V with multimeter on duet gen 2, duet report 24.0V and power supply voltage is 24.80V at 17A. So voltage drop with 50cm wire must be taken into account, and the duet is very good



  • @pipersw I measured mine at the input terminals of the duet so any voltage drop due to wiring was already taken into account. The 0.3V difference that I saw is well within the +_3% accuracy that DC quoted for the duet gen 3 main board.


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