what is "I" in pid ?

[kamenges]

I agree the PV looks like it may have taken a shot from a derivative at setpoint change. The thing that I find odd is that there is nothing in the CV that suggests that. It's like the PV and CV graphs are from two different processes.

Originally posted by Paully's5.0:

By understanding the rate of change, we can start to predict the future.

I've never been a big fan of the whole "predicts the future" thing when discussing derivatives. It makes the use of the derivative seem "magical" to people who are just trying to grasp it.

When I talk about the derivative in a PID to people new to it I generally refer to an automotive shock absorber (dampers to those outside the U.S.). The faster you try to move the thing you are concerned with the harder the derivative will fight to keep it still.

The problem with the derivative is when the feedback lies about the process velocity. This is where people start talking about the derivative causing all sorts of chatter and noise. It isn't specifically the derivative; it is the feedback.

Keith

[Oceansoul]

I was reading an old manual at work earlier for Heenan Inverter drives and in there is this basic explanation of PID control. Not the most scientific, but i found it quite helpful.

[Peter Nachtwey]

Originally Posted by kamenges

I've never been a big fan of the whole "predicts the future" thing when discussing derivatives.

Me neither. The derivative term adds damping. The derivative gain can be used to place a pole. The derivative gain can also be used to extend bandwidth.