On 1/25/15 1:30 PM, WarrenS via time-nuts wrote:
I second Poul-Henning Kamp's comments concerning D-terms, (mostly) as done in the TBolt and likely other GPSDOs.
Bear in mind that a PID loop is basically a fairly simple control loop that is easily susceptible to linear analysis. They're simple to implement with analog controls, they're simple to analyze, and for a whole lot of applications, they'll work just fine.
And there's decades, if not centuries, of experience with P, PI and PID controllers in a practical sense. A lot of people know how to *tune* the parameters based on observed system dynamics.
But for a lot of systems:ones where there are significant nonlinearities and/or time delays and/or saturation/limiting effects a PID loop might not be a good choice. (for instance, if you're doing a closed loop position control with a stepper motor as the actuator, with a small motor and a big heavy load, with low friction...)
For myself, I am seduced by the idea of a control system that builds and adjusts a model of the system being controlled, and then derives the needed control inputs from inverting that model (whether arithmetically, or by some clever algorithmic means).
For instance, a PID controller doing temperature control doesn't have a *good* way of incorporating side information like the outside temperature. There's all kinds of schemes for doing this (double loops, extra terms, etc.)
_______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
