Temperature hysteresis doesn't work properly

Discussion in 'MSI AfterBurner Overclock Application Discussion' started by DaRkL3AD3R, Feb 17, 2020.

  1. DaRkL3AD3R

    DaRkL3AD3R Member

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    GPU:
    GTX 1080 Ti STRIX OC
    I've been experiencing this for a long time now across many versions of MSI Afterburner but basically my custom fan curve looks like this:

    0% from 0c to 40c
    30% from 40c
    60% at 80c

    I set temperature hysteresis to 10 degrees so that if I am playing something low GPU load that would otherwise keep the GPU bouncing between 31-40c, the fan doesn't keep shutting off constantly.

    The problem is, the fan will randomly ignore the hysteresis setting and just switch to 0% if below 40c for seemingly no reason. This is most prominent when exiting a game that loaded the card and then browsing idle on the desktop in 2D power states. It will cut off the fan at say 35c instead of waiting to reach 29c.

    Why is this happening? Is it a bug with MSI Afterburner? Is there some underlying code that only applies hysteresis during certain situations?
     
  2. Unwinder

    Unwinder Moderator Staff Member

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    It is not a bug. You’re misunderstanding hysteresis functionality, it doesn’ work the way you’re assuming. Use search please, I’ve explained how it is supposed to work in_details_ before.
     
  3. AsiJu

    AsiJu Ancient Guru

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    If your fan switches off at 35 C with hysteresis of 10 C that means your GPU started cooling down from 46 C.

    That's how hysteresis works mathematically, when X value (temperature) starts decreasing, the corresponding new Y value (fan speed) will be applied only after delta X is larger than hysteresis.
    (and because 35 C is on the 0 % area of the curve you defined, fans switch off).

    BTW: make sure your fans are able to start up and operate properly with a speed of 30 %.
    If you try to use too low fan speed values, this can lead to inconsistent fan functionality.
     
    Last edited: Feb 17, 2020
  4. Andy_K

    Andy_K Master Guru

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    I believe this is the explanation from Sep 24, 2010(!) he is referring to:
     
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  5. DaRkL3AD3R

    DaRkL3AD3R Member

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    AsiJu I set 30% because my fans don't spin properly until around 25% so to be sure I use 30% as the base minimum.

    So then there is no real way to get my desired results here? Where at 40c the fans kick on and stay on until the GPU cools back down to 30c or lower? There will always be some variability based on the peak temp when cooling began?
     
  6. AsiJu

    AsiJu Ancient Guru

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    Well if you want to make sure fans stay on until 30 C then define the first range as:

    0% from 0 C to 29 C

    of course in turn this means that fans also start up already at 30 C when temperature increases.

    Experiment with different ranges and hysteresis values for best results. Consider adding more intervals to the curve too.
     
  7. AsiJu

    AsiJu Ancient Guru

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    Hey one thought / idea about your fan curve:

    30% from 40c
    60% at 80c

    does this mean fan speed increases linearly from 30 % to 60 % when going from 40 C to 80 C?
    Because if you want to achieve both fans starting up at only 40 C but also staying on until 30 C, then define a new interval, for example:

    0% from 0c to 40c
    30% from 40c to 50 C (flat)
    from 30 % at 50 C
    to 60% at 80c

    if the description quoted by Andy_K is literally accurate then values causing fan speed change are used as latch points for hysteresis.
    In other words a flat curve should record only the start point as fan speed change, therefore if your GPU starts cooling down while between 40 C and 50 C, hysteresis should still use 40 C as reference.

    So if you still keep 10 C hysteresis that should in theory mean your fans won't stop until 30 C.
     
    Last edited: Feb 18, 2020

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