PID controllers help
 

I am having a very hard time trying too understand how PID controllers work, and how to use them in labview. If anyone has any info on PID, or know a good tutorial on them, would they please let me know.

Re: PID controllers help
 

Google "PID controller" and you'll get lots of hits.

Use Chief Delphi search and you'll find lots of recent threads about PID controllers.

Search the LabVIEW help for PID and you'll find a LabVIEW-specific explanation and some examples.

Re: PID controllers help
 

The first step is to understand what a PID controller is trying to do.

A simple example is a cruise control on a car. The PID controller there wants to keep the car's speed constant, and correct any changes to the speed within a reasonably brief time..

Let's say you want to maintain 55 MPH, which we call the "setpoint". If the car's speed is 25 MPH, we have an "error" of -30 MPH. If we allow the P (proportional) factor to do its thing, it asks the car to accelerate, in proportion to the error - bigger error, more acceleration.

But we don't want to accelerate at full throttle, so we? That much power might cause the car to be unstable on the road, so we limit the maximum acceleration regardless of the "error" to some value - this is the D (derivative) factor.

OK, once we get to 54 MPH, the error is small, but not yet zero. The acceleration requested by P is less than the D limit, but the car might take an unreasonably long time to finally reach 55 MPH. So what we do is use the I (integral) factor to add up the error over time, so that in a relatively brief time even a small error is handled and brought to zero.

I hope this helps. In the real world, we often don't even need D or I, with P being sufficient for many tasks.

Programming PID is actually quite simple, but tuning the P, I and D factors can take some tedious trial and error.

Re: PID controllers help
 

This paper has been one of my favorites to recommend when it comes to PID. While it's written for an embedded micro controller system in C the principles are the same and you should be able to gain some deeper understanding from it.

http://www.eetimes.com/design/embedd...-without-a-PhD

The full article PID without a PhD was published in the October 2000 issue of Embedded Systems Programming magazine. It is written to provide the embedded software engineer with a simple design method for writing a PID controller in software, without requiring any formal knowledge of control theory.

Re: PID controllers help
 

Recently I found a PID article written for Lego Mindstorm. It is actually quite good and quite detailed. Portions of it are a bit deep for elementary school, but for the most part, quite easy to follow.

Re: PID controllers help
 

When manipulating your PID values on your robot, the I value will generally be a very low number (or at least it was for our robot). You will want to change the P and D values, changing the I value slightly will make a big change in your robot. Also, make small changes to each value and test that value, doing a large change in value will not be good. I have personally seen our arm crash down and smash our pneumatic board and break a few solenoids.