PT1000 Duet Wifi - Resistor Swap

  • I currently have a v1.04 Duet Wifi and want to upgrade my temperature sensing setup for my hotend, looking for better accuracy. I initially considered using a pt100 but then got very interested in the pt1000 due to the similar max temp range and ease of setup (just plug and play into my smart effector). As I kept reading into it, however, I saw that the 4.7k series resistor may not be the best for that. After reading another forum post discussing a similar issue, @dc42 recommended using a 2.2k .1% series resistor as opposed to a 1k as recommended by triangle labs for better high temp resolution. From what I understand (which I admit is fairly limited) this is because you get the best resolution when the measured resistance of the probe is the same as the series resistance. Is that true? If so, if I just want to print pla, why not use a 1.8k series resistor as that is the resistance of the pt1000 at 200c (The table of pt1000 resistances at different temps can be found here, FYI this is, as far as I know, only for the sensor found here)? I get that most people won't buy a pt1000 just to print pla, but I'm more wondering about if I'm right about what the value of the series resistor means in terms of resolution. Thanks!

  • administrators

    Yes the reason why a lower value resistor is preferred is to get better resolution from the PT1000. If we ignore ADC oversampling (which theoretically should improve resolution), the available resolution with various series resistors at 20C, 180C and 260C is:

    Using 4K7: 0.44C, 0.57C and 0.64C
    Using 2K2: 0.30C, 0.45C and 0.53C
    Using 1K8: 0.28C, 0.44C and 0.53C
    Using 1K0: 0.26C, 0.47C and 0.59C

    So 2K2 or 1K8 are a little better than 4K7, but at typical printing temperatures 1K0 is worse.

  • @dc42 so you gain 0.11 in resolution by swapping the resistor from 4K7 to 2K2? Is it even worth doing? I ordered a PT1000 element now for high temp printing and got thrown off by the recomandation of swapping resistor. When I see your estimations I wonder if it's worth the hassle at all. If I gain +/- 0.11 in accurancy by swapping I won't bother with it 😛

  • administrators

    IMO it's not worth doing. But if you do want to, then the simplest way is to solder a 3.9k resistor in top of the existing 4.7k one.

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