PID controllers (was RE: Holley ecu info)

[swagaero]

Tom Cloud wrote:
> 
> >Hi All
> >
> >       Tom mentioned pid controllers in his last post. Would someone please info
> >me on how they work? Have seen so minor descriptions, but nothing in depth.
> >
> >Thanks Vance
> 
> Vance .... I'll try to make it brief (to keep from showing my ignorance)
> 
>  - all amplifiers have two inputs (even "single-ended" op-amps, etc)
> 
>  - one input is compared to the other and the difference is amplified
> 
>  - on single-ended inputs, the "reference" is ground
> 
>  - on a controller, one input is usually called the "reference" or set-
> point and the other the "error" or feedback
> 
>  - a simple controller just multiplies the difference between the two
> inputs to yield an output "proportional" to that difference
> 
>  - a simple proportional controller can only "see" -- or correct for --
> errors which are greater than the reciprocal of the gain (ex. with
> a gain of 1000, errors of 1/1000 or less are not "seen", hence not
> corrected)
> 
>  - to "close the gap" in the proportional controller, an integrator
> is incorporated.  The small error not corrected by the proportional
> function is continuously added back in over time (integrated) until
> it grows large enough that the gain of the system can correct it.
> 
>  - the differential part is to keep the system from over-reacting --
> i.e., fast rising errors will cause the gain of the system to be
> reduced to keep the output from going berserk

Ringing of a false signal or referance from a high voltage signal (ie
ignition coil) will drive any opamp up a wall

Steve
> 
> That's my thumbnail sketch  ....  anyone care to correct and/
> or add to it ??
> 
> Tom Cloud
> 
>       Insanity is hereditary, you get it from your kids!