Temperature Hysteresis?

Discussion in 'MSI AfterBurner Overclock Application Discussion' started by Strider, Sep 23, 2010.

  1. Strider

    Strider Active Member

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    I am new to MSI Afterburner and I am trying to figure out how this setting works, but without much luck. What does it do and what do I need to set it on?
     
  2. mkchiu

    mkchiu Member

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    Neat new feature. I've never used it in Afterburner, and the hint was written in a way that implies a hardware-style implementation.

    For a hardware-style implementation of hysteresis set to 10C, you should have the following fan behavior. That is, fan turns on 10C early and turns off 10C early.

    [​IMG]

    Turn on logic would follow red curve, turn off logic would follow blue curve. Both are relative to green set point curve, but offset up and down by 10C.
     
  3. Strider

    Strider Active Member

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    So tell me if I get it right >> When I have made a fan profile, and for example I take 1 point, the fan starts blowing at 70 degrees with 80% fan power, a temperature hysteresis of 10 degrees will let the fan start at 60 degrees with 80% fan power, and when cooling down faster then heating up it will decrease fan power at 90 degrees to 80% fan power?

    So all it does is starting and stopping earlier according to the temperature difference filled out at the temperature hysteresis settting?

    If that is so, won't the GPU stay to warm because it starts lowering fan power to early?

    Edit: Right now I made a very aggresive fan profile to cool down my GTX470 as much as possible, it looks like this:

    Degrees (celsius) / Fan speed (%)
    40 / 60
    50 / 70
    60 / 80
    65 / 90
    70 / 100

    Why would I want to start and stop earlier? What are the benefits of that? If it starts earlier it hasn't got much use yet, if it stops earlier my gpu will quickly rise in temperature again.
     
    Last edited: Sep 23, 2010
  4. mkchiu

    mkchiu Member

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    Hysteresis is generally not useful with such steep control curves. I picked an excessive 10C as a quick, easy to illustrate example.

    Not exactly; GPU does not stay warm because fan is slowed early...

    Hysteresis keeps the fan at a higher fan speed more often than not. Less fan earlier means higher temp, with higher temp and hysteresis, fan will be forced back to higher speed. So for steep curves, fan would be rarely go below the max speed you set.

    For example, temperature falls (red arrow) and fan slows, then temperature rises, so set fan to the rising or higher fan speed. Or fan resets to 100% until temperature drops past green line.

    [​IMG]
     

  5. Unwinder

    Unwinder Moderator Staff Member

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    The picture with red/blue curves is a bit incorrect. And quite opposite, hysteresis is the very useful with step control curves, because it greatly minimizes unwanted and too frequent fan speed fluctuations when the temprature is floating around step points. Just imaging that you have the following step fan speed curve:

    50% for temepratures lower than 70C
    100% for temeperastures higher than 70C

    Without hysteresis once the temeprature crosses 70C limit (e.g. changes from 69C to 71C) fan speed changes to 100%. Then GPU is cooling down to 68C due to increased fan speed and fan speed iimediately changes to 50%. So temeprature may easily fluctuate near 70C limit causing fan speed to change up and down frequently. And such changes in fan speed are really annoying. And most of hardware fan controllers are using hysteresis to prevent fan speed changes in such situation.

    Now imagine that you define hysteresis of 5C. Under the same conditions fan will speed up to 100% when temeprature changes from 69C to 71C, then fan control loop will latch the temeprature causing fan speed change (71C in our case) and it will not allow fan speed to decrease back while the temperature is higher that 71C-5C = 66C.
    BTW, hysteresis is applied to decreasing temeperatures only, not to both directions like mentioned in this thread.
     
  6. chanw4

    chanw4 Ancient Guru

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    So the red line in the graph should be speed reduce control while the green line is is the speed up control?

    And you mentioned it works good with step control. (are you talking about the graph which looks like a step??) Does this setting work with or work effectively with the straight line graph? (where the temp is decided by the steep?)
     
    Last edited: Sep 24, 2010
  7. Strider

    Strider Active Member

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    Aah I finally get it! I have set it to 5 degrees, which seems to work fine! My GTX470 is 41 degrees average in Windows, and 65-70 degrees while gaming (80 degrees on furmark, but games never seem to reach that, even not Metro 2033.
    Pretty good for a GTX470 in an air-cooled system :D

    (without afterburner fan profile it is about 10-15 degrees warmer at every point I mentioned)
     
  8. Unwinder

    Unwinder Moderator Staff Member

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    Not exactlty. Hysteresis cannot be correctly represented by such red line displayed next to main green fan speed curve, because fan speed decrease rule is not linear when hysteresis is in use. Hysteresis adds delay (based on latched and current temerpature difference) to fan speed decrease rule, it doesn't simply shift the main curve like that picture shows.

    I'm talking about one of two fan curve representation modes using the terms of Afterburner context help. The modes can be toggled by double clicking the curve editor window area. Step mode assumes that each curve node defines new fan speed toggling point whilst linear mode lineary interpolates fan speeds between each pair of nodes.

    Yes, it does work and it does work effectively with both step and linear mode.
     
  9. chanw4

    chanw4 Ancient Guru

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    Thanks, just found the sin graph you posted on this forum and it shows how it works, Guess I should have read that thread beforehand.

    http://forums.guru3d.com/showthread.php?p=3570421&highlight=Hysteresis#post3570421
     
  10. mkchiu

    mkchiu Member

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    Nice. It's good for me to learn how a (better) hysteresis design should work. Thanks.
     

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