VIDEO: PID Loop Tuning Explained – Part 2 – Proportional and Integral

Here we are rolling right along into Part 2 of the PID Loop Tuning Explained video series. In this part we are now looking at the incorporation of the Integral or ‘ I ‘ portion of a PID Loop. This is pretty much the most common form of a PID Loop even though everyone says P.I.D. In most cases the math behind it is just the P and the I portion.

The Integral portion is what I consider the portion that does all the work when someone mentions that their PID controller is ‘AUTO’-tuning. The Integral portion continues to hone in on the set point with much less drastic jumps and even without the input changing. Let’s check it out!

If you want to see it in HD don’t forget to click the small 480p in the lower right corner and select 720p HD.

It’s ALL About the Little Things

Some people are satisfied and happy when they get something close to what they want and well that is wonderful for them emotionally. Unfortunately programming a controls system is less forgiving about being ‘sorta right’. People who have worked with me might say I am picky and … they are absolutely right! LOL So with PID Loops I really aim to get it right and get right as fast as possible.

The main reason we want to add Integral control of the PID is so that when our input is not moving or not moving rapidly enough towards meeting set point we can introduce a little bump to the resulting PID output percentage. This will in effect continue to adjust the PID to get closer and closer to making the input and set point match.

Another great feature of using the Integral portion is that it will help some in large drastic swings. Now those who know a little about PIDs might be saying, “HOLD IT! HOLD IT! HOLD IT! That is what the Derivative does.” Well we will talk more about the Derivative in the next video, but the Derivative helps drastic swing based on the speed at which the difference between input and set point occurs, not necessarily the distance apart they become.

It’s OK to be Laggy

I play XBOX and Computer games and anyone else who does, knows LAG is your worst enemy. You don’t want to be reacting now to something that happened 5 seconds ago otherwise it’s respawn and try again. But, if you are a PID controller or the DDC controls technician tuning one, life isn’t so bad if you lag a little. (Take a quick look at that robot video and you will see how the second robot seems to be a little more laid back than its tweaking meth addicted counterpart.)

Now to Cool Those Peeps in that Sun Filled Room

In Part 1 we got the room to come down to 75°F from 80°F, but as the input or room temperature got cooler the valve began to close based on the difference from set point. But now with the Integral built in the PID percentage will continue to increase. In fact, back when the room temperature was getting cooler and the Proportional Band was causing the PID output percentage to decrease the Integral would have continued to tick up the Bias.

Doing this would cause the lag I have been describing because even though the Proportional Band wants the PID percentage to go down (and it will decrease), it won’t go down with such a big jump because the Bias will be increasing to say 60 from 50 and cause a bit of an offset from the full swing. You could imagine the Bias or the effect of the Integral portion of the PID as a trailing stop. It moves a little slower than the reactions of the Proportional Band, but it is always moving even when the input or set point are not, therefore allowing to eventually get right on top of set point.

 

Alright, that was awesome and I’m glad you are following this video series. The next video will be a short one, discussing the Derivative portion of a PID. The reason it will be short is there really isn’t much to see in the way you actually set the parameters or watching the resulting PID output percentage, but I will use some graphs of the actual Indoor Humidity Control System I was working on when creating this series.

Do you have any What-Ifs so far about PI Loops? Let me know in the comments below and I will be sure to add answers to your questions in the later parts of this series.

 

You can view all the other videos in this series at the PID Loop Tuning Explained Video Training Series post.

One Response to VIDEO: PID Loop Tuning Explained – Part 2 – Proportional and Integral

  1. waheed November 13, 2013 at 02:01

    Are u good teaching.
    if u any video share.

    Reply

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