PI Regulation - Notes from the queue.

Discussion in 'Info & Guides & Reviews' started by SandbagJohnny, Jun 30, 2017.

  1. SandbagJohnny

    SandbagJohnny New Member

    Jun 28, 2017
    Likes Received:
    This information was collected from the issues comment threads from the MyEvic (ClockSelect) and Arcticfox projects on the Github repo. The bits relevant to Articfox are reposted here for posterity, as github is no longer used... Hopefully none of it is outdated :) Thanks NFE Team!

    • The PI-regulation algorithm is based on Celsius. The base temp is always 0C.
    • Range is the percentage of the target heat at which to begin PI regulation. (0% will use PI as soon as the button is pressed. 100% will use PI only when the set temp is reached. ie- 200C and 50% Range = PI regulator is switched on when coil temp exceeds 100C)
    • PI-Regulator has higher priority than preheat. To make preheat work in conjunction with PI-Regulator, use a range value above 0%.(usually 30-40%)
    • P gain value limits: min: 0, max 6000
    • I gain value limits: min 0, max 9000
    • Using PI-regulation, you don't care what your ramp up wattage is; just set it at [your device's rated max setting] and forget it. The PI-regulation will just take what it needs.
    • P is in mW/°C, that means the controller will drive the power to P*δT mW, where δT is the wanted increase in temperature.
    • I is in mw/°C/s, that means the controller will drive the power to I*δT mW/s, where δT is the wanted increase in temperature over time.

    P = some_value * mW / C (temperature error)
    I = some_value * mW / C / s (temperature over time)

    Temp control issues

    In most cases problems arise from these issues; Using PI mode is reported to work well for:
    • Bad TCR from mismatched multiple coils
    • Bad TCR from multimetal coils

    Things that will adversely effect TC performance that firmware won't fix:
    • Transient shorts (SS doesn't work as well with contact coils vs spaced coils In TC mode. In Wattage it's usually not as noticeable because a transient resistance spike doesn't effect the regulator in real time like it does in TC mode.)
    • Build resistance too close to the edge of the acceptable allowed range for the wiretype.

    Some essays on PID regulation

    Easy reading PID guide
    Moderately in-depth PID guide

    [Additional feature testing notes]

    In my own testings with plain 28ga SS316L in a single coil set up vs some twisted/etc wire, the default P value of 1850 in Arcticfox appears to be set up for a more 'exotic' (multi-coil, claptons, tcr/resistance issues, etc) build; if you're using something like a plain wire single coil the p value can be much lower. (between 300-800)

    Test Settings:

    • 28ga SS316L single vertical spaced coil
    • 316L TFR mode
    • PI regulation ON.
    • No preheat.
    • Ramp up 75w.
    • Range = 0%
    • P = 300
    • I = 300


    Stock algo, ramp up @ 20 watts
    Stock algo, same ramp up as used in PI tests
    PI regulation with above listed settings
    #1 SandbagJohnny, Jun 30, 2017
    Last edited: Sep 10, 2017