4 ms·

Why won't it help if there is no delay? What system truly has no time delay and no inertia? PID systems are basically a differential equation and optimal coeff

by kortex 2y ago

Why won't it help if there is no delay? What system truly has no time delay and no inertia? PID systems are basically a differential equation and optimal coefficients are just solutions to that system which maximize responsiveness and minimize ringing, so I would think the effect of decreasing time delay just adjusts the Ki and Kd to account for the smaller Tc value.

dahart 2y ago
All physical systems have time delay, but software doesn’t necessarily. I bumped into PID controllers writing software for video games where I had the option to not have a time delay in the system, if I wanted to do something less physically realistic. In a game, you can (and I often did) use a proportional-only controller for certain things. Then I got surprised when that didn’t work, after a time delay was introduced. I mainly called out the time delay because the delay is what causes the problem that needs solving, so it seems reasonable and important to state. But I wouldn’t argue with anyone who said the delay part seems obvious. ;)
- entropie 2y ago
  > but software doesn’t necessarily. Is this true? I mean the delay may be inconsiderable but there is a delay, right?
  - dahart 2y ago
    It depends entirely on what you’re doing in software, but yes it’s true that you don’t always have a delay. Your simulation doesn’t have to involve time at all, so that’s one way you might not have delays. But if you do have a simulation involving time, and your update of some entity in the system can change it’s behavior instantaneously, then there’s no delay. Like I said, in a game you can choose whether your AI has to follow physics or not. It is easy to make a non-physical car that can turn instantaneously. When you do that, a P-controller works just fine. As soon as you make it follow physics, which adds time delay between input and response, then you have to have the I & D terms, otherwise your car will be unstable. In video games it’s very common for cameras to try to follow something (like your avatar) smoothly using a P controller, they are a good example of a very common bit of software that has no delay - they can follow and turn without being subject to physics, and thus they generally don’t need the I & D terms of a PID controller.
  - bgnn 2y ago
    not necessarily. feedforward path delay can be zero. typical mistake done while modeling feedback systems in SW.

by kortex 2y ago

dahart 2y ago

All physical systems have time delay, but software doesn’t necessarily. I bumped into PID controllers writing software for video games where I had the option to not have a time delay in the system, if I wanted to do something less physically realistic. In a game, you can (and I often did) use a proportional-only controller for certain things. Then I got surprised when that didn’t work, after a time delay was introduced. I mainly called out the time delay because the delay is what causes the problem that needs solving, so it seems reasonable and important to state. But I wouldn’t argue with anyone who said the delay part seems obvious. ;)

entropie 2y ago
> but software doesn’t necessarily. Is this true? I mean the delay may be inconsiderable but there is a delay, right?
- dahart 2y ago
  It depends entirely on what you’re doing in software, but yes it’s true that you don’t always have a delay. Your simulation doesn’t have to involve time at all, so that’s one way you might not have delays. But if you do have a simulation involving time, and your update of some entity in the system can change it’s behavior instantaneously, then there’s no delay. Like I said, in a game you can choose whether your AI has to follow physics or not. It is easy to make a non-physical car that can turn instantaneously. When you do that, a P-controller works just fine. As soon as you make it follow physics, which adds time delay between input and response, then you have to have the I & D terms, otherwise your car will be unstable. In video games it’s very common for cameras to try to follow something (like your avatar) smoothly using a P controller, they are a good example of a very common bit of software that has no delay - they can follow and turn without being subject to physics, and thus they generally don’t need the I & D terms of a PID controller.
- bgnn 2y ago
  not necessarily. feedforward path delay can be zero. typical mistake done while modeling feedback systems in SW.