Agreed 100%. I would just add that when all else fails, apply
experience....and also.....There will be hysteresis in EVERY control
loop..it's just a matter of how much is acceptable.

Chris

> Short PID 101:
>
> PID = Proportional Integral Derivative
>
> Proportional control means that the correction is proportional to the
> error.
>
> Correction = -1 * P * Perror = -1 * P * (Setpoint - CurrentValue)
>
> Integral control means that the correction depends on the
> present and past
> error. More exactly, the Integral of the error, which can be
> represented
> as the sum of the errors so far. If Ierror0 is the error at
> the previous
> measurement time and error is the Ierror at the present time then:
>
> Ierror = Ierror + (Setpoint - CurrentValue)
> Correction = -1 * I * Ierror
>
> Derivative control means that the correction depends on the
> change rate of
> the error. Therefore if Derror was the previous error:
>
> Derror = Derror - (Setpoint - CurrentValue)
> Correction = -1 * D * Derror
> Derror = (Setpoint - CurrentValue)
>
> By putting it all together and everything in the middle of a loop that
> repeats at fixed time intervals:

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