Lawrence Lile wrote:
> 
> Yes, I've done some PID controllers.  There are a few basic questions:
> 
> 1.  Do you have on-off or proportional control of your Peltier junction?
> 2. How fast can your system respond - tenths of seconds, seconds, or tens of
> seconds?
> 3. YUou might set your loop time - how often you measure, to be something
> less than the amount of time your system can respond, but not too much less.
> Way longer ansd the system gyrates wildly, way shorter and you'll be going
> 100% one way and 100% the other way in no time.
> 
> Here's a basic approach to PID:
> 
> 1.  Measure your input variable (temperature) and decide if it is too hot or
> too cold (via the reflection technique)
> 
> 2. Subtract your measured variable from your desired variable.  Call this
> DIFFERENCE
> 
> 3. P = DIFFERENCE * Pconstant.   Pconstant is the first critical thing
> you'll have to tune in.  Start by trying 1/4 to 1/10.
> 
> 4. I = DIFFERENCE * Iconstant + OLD I     keep a running tab of how far you
> are from the setpoint.  Start with a small number, 1/100.
> 
> 5. D = (NEW DIFFERENCE - OLD DIFFERENCE) * Dconstant.  Once again, Dconstant
> should be small.

Good advice. I have noticed another thing that can make your 
system much more immune to the low-frequency I-oscillations : 
Reset the I-value to zero whenever P=0.

-- 
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