PID Loop Learning

TL140

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Join Date
Jun 2014
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South Carolina
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Hello all.

Kinda-Sorta related to PLCs, but does anyone know a good place to learn about PID loops, applications, and tuning? I have a very small understanding after watching a few videos, but so far it has all been theory and not applications or numbers. Like I understand that the proportional control is used for bang bang processes like a thermostat I presume. From the material I have read, the integral part is like a reset tick rate. Still a little fuzzy on that because I though the integral was the accumulation of a function? And for the derivative, I honestly cant find anything too clear and have no understanding of its role.

Also, another question. Are PID loops mainly used with all analog components?

Thanks,
TL
 
TL140 said:
Hello all.
Also, another question. Are PID loops mainly used with all analog components?
Click to expand...

Hi!

I am by no means an expert, but in my opinion you are right. PID is used for continuous signals.

However, three-point-step controllers (step up-wait-step down) usually use a PI controller.

I just started using Matlab with Simulink for some controls simulation and it makes it a lot easier to understand. You might want to check that out.
 
The links listed above are good resources. Permit me to provide another. My boss at my first job provided every engineer with a copy of this book. It's been a good resource over the years and provides practical application techniques for PID loop tuning.

TL140 said:
Are PID loops mainly used with all analog components?
Click to expand...
Usually, but not always. I've seen temperature loop control done with a steam/coolant two-way valve where the output of the PID was used to vary the valve cycle on time. Not nearly as efficient as a throttle valve with positioner, but it can be better than nothing.
 
Let me also throw in this guide by Gregory McMillan. He has written a number of books on control, and is a wealth of knowledge on the subject. I attended one of the ISA courses on PID control that was lectured by him, and came away with a much better understanding.
 
Peter Nachtwey said:
I wonder if any of those books cover pole placement. Pole placement is the key to really understanding PID control. Other method are just trial and error and tweaking gains without true understanding.
Click to expand...

The book I posted covers this and more. Pole placement, root loci, etc.
 
A PID control works with the difference between the setpoint and the measured value.
suppose you are driving on a highway in lane 3.
the setpoint is changed to lane 2, so the difference is 10 foot(sorry i am from europe) If the Kp is 1%/foot the steer will go to full 10% (so 50% is middle thus the steer will be at 40%, the nextis 9 feet so the steer will be 41% and thus the car will slowly go to next lane.
Next step I the road has a curve in it, it would mean the car would be 10 feet off in a curve. the I looks if the difference the last time, and will give the steer small extra everytime again.
The D gives a swing to the steer to get a little faster to other lane.

The big drawback on standard PID is it does not look at the speed of the car.
A fuzzy (you mentioned it) control will be an expert in this.
 
This is a good problem to illustrate a point! Time for a quiz!!!

shooter said:
The big drawback on standard PID is it does not look at the speed of the car.
Click to expand...
Sure it can!!!!!! Now how do you do it and I mean the right way????? Anybody?

A fuzzy (you mentioned it) control will be an expert in this.
Click to expand...
Fuzzy logic is an attempt to solve the problem without understanding the system.
 
Peter Nachtwey said:
Sure it can!!!!!! Now how do you do it and I mean the right way????? Anybody?

Fuzzy logic is an attempt to solve the problem without understanding the system.
Click to expand...

You don't have to put the PID on position, if you put the PID on the velocity control. You are now controlling speed.

Typically correct on your fuzzy logic comment.
 
i do not agree with you peter, although it is often thought to be that way.
I see Fuzzy more as a expert system, so with the knowledge of an EXPERT you make a control system. I have a demo with 3 distance sensors in a racecar taking a course.
I think fuzzy is often misunderstood, i am calling it more a expert system.
PID is so easy with autotune anybody can do it. (but only good for one situation)
 

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