PID controllers (was RE: Holley ecu info)

[Tom Cloud]

>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

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!