PID question

No worries. Well, maybe.

Ignore the compensation things.... like ignore the capacitors. Just have a look at the way things go up and down to see that they do the right sort of thing. This bit goes up so this bit goes down and takes away from that bit and then the other bit gets taken away from the first guess and things balance themselves out.....

It's sort of cute because the error amplifiers, U1 and U2, are inverting configurations and, if you need to, that makes it easier to clamp their outputs to sensible levels.....

On the other hand you do need dual supplies for your op-amps.

Of course TBW (TopBossWank) will have some sort of mental tick over that one and you might feel the need to waste a lot of time trying to find a way around it. Obviously TBW knows best.

If you value your sanity then don't waste too much time thinking about it. Mind you, I don't want to seem like an old fart.

TBW always asks these sort of questions because if you can find the answer to his problem he can say he has saved tuppence a unit whilst ignoring the extra sixpence it cost to get there and the fact he had to dump his original specification..... Then you get to sort out the recurring problems.

Even if you do choose to go the digital way you will still need to look at things in an analog way if you want to progrim things proper like.

I will tell you this....

You're some sort of smug bastard on the quiet. Obviously they can, it's just that your crappy analog electronics isn't fast enough to make it viable. Instead of sitting on the sidelines and sniping you should get your finger out.

DNA

I confess to some surprise at not understanding the difference between control signal and error signal. PID stands for proportional, integral, and differential components for the the control process. Using an error signal for the PID input is a fools errand. Properly used, proportional sets the final response, integral provides smoothing, and differential provides response speed. Direct error signals are not useful.

This is the underlying concepts for "Kalman filtering" which take into account device response characteristics to determine optimal control outputs for the highest performance and reliable stability.

The control signal is usually the output from the error amplifier that drives some control device (pass transistor, in this case)

This depends on whether the setpoint is changing or fixed, and whether or not you want fastest response to both setpoint changes and load disturbances, or just fast response to load changes and slow, over damped response to setpoint changes (like turning the voltage setting knob on the supply). There are several useful combinations.

Integral provides eventual perfection, since it keeps changing the output (ever more slowly) till the average error is zero.

Another way to look at PID response is as a soft notch filter. Any feedback process develops a conjugate pair of poles that represent the onset of oscillation (a peak in the feedback response. If you can center the response notch of the PID combination (falling gain with rising frequency from the integrator term to some minimum gain from the proportional term, with rising gain above that minimum from the derivative term) this response peak, you extend amount of closed loop gain tolerated and the frequency range of stability. Some versions of PID terms have deeper possible notches than others. The more deeply notched versions work better with inherently resonant systems.

Lots of useful lead lag phase compensation networks used to tweak feedback systems can be described as a P. I. and/or D. terms.

I think that Kalman filter control also takes the noise of the measured variable into account, combining some part of the control output run through a system model that predicts the result of control changes with some fraction of the measurement of the system, to improve the control you can achieve based strictly on a noisy measurement. Ideally, the proportions of predicted response and measured response adjust in response to the noise. Please correct me if I am misunderstanding it.

Yes, i am suggesting that OP move across the error amp to the reference value / input.

Yes, PID controllers have the added ability to change the P, I, and D values in a running system.

Doesn't seem like it to me.

(snip)

See:

Nice links, the wiki still hits the hard math a little too quick and not enough explanation. The second link is really good. I could probably use it to learn the deep stuff that is hard follow in the wiki.

I have been reading about Kalman filters for a long time, but I haven't yet had an industrial control application that cried out for it loud enough to make me learn how to actually use it. One of these days, perhaps.

I have managed to apply a couple of Smith Predictors, which are sort of related but deal with delay in a control loop, instead of noise.

Another good site. I suspect you would end up teaching me very quickly.

(snip)

You might be able to learn very quickly, but I doubt I can teach quickly. ;-)

That's ok. stay in this NG, your expertise is very welcome.