You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old April 20th, 2017, 02:23 AM   #1
Peter Nachtwey
Member
United States

Peter Nachtwey is offline
 
Peter Nachtwey's Avatar
 
Join Date: Apr 2002
Location: Vancouver, WA, US
Posts: 6,469
Advanced Control: Rant!

I have yet to see a good video about PID control on YouTube.

Even the college professors are clueless. It is no wonder so many think PIDs are black magic. The students are being cheated.
__________________
"Living is easy with eyes closed, misunderstanding all you see...." Strawberry Fields Forever, John Lennon
  Reply With Quote
Old April 20th, 2017, 02:50 AM   #2
cardosocea
Member
United Kingdom

cardosocea is offline
 
Join Date: Nov 2016
Location: London
Posts: 158
There's an easy fix for that...
  Reply With Quote
Old April 20th, 2017, 04:01 AM   #3
AustralIan
Member
United Kingdom

AustralIan is offline
 
Join Date: Jan 2013
Location: UK
Posts: 417
8 hour video tuning a slow not-so linear loop?
  Reply With Quote
Old April 20th, 2017, 04:27 AM   #4
doomsword
Member
Croatia

doomsword is offline
 
Join Date: Aug 2016
Location: Zagreb
Posts: 70
How would you teach someone automation theory and show it makes sense in real life?
Because every day at work I see people don't know even basics, like what's the difference between open-loop and closed-loop response.

On the other hand I know what's happening, but I have no knowledge of how to implement it, manuals are basically meant to make you rely on certain vendor products and their implemented solutions. They're not there to teach you how to analyze and solve problems.
  Reply With Quote
Old April 20th, 2017, 04:58 AM   #5
HJTRBO
Member
New Zealand

HJTRBO is offline
 
HJTRBO's Avatar
 
Join Date: Jul 2008
Location: Melbourne
Posts: 584
D for Do Not Use

PID was a black magic for me as a sparky for years. I could make it work smoothly on a simple process without the D.
It wasn't until I undertook further education where there was engineering calculus involved that I then fully understood what was happening with the I & D terms. Also in the course was basic first order DE's.
With this knowledge I was able to use Matlab & Simulink to set up simple first order processes with various dead times and play. Now I see the terms in a much brighter light.
In my personal experience, that little bit of higher education has unraveled the 'Black Magic'.
Now, weather that is achievable on a You Tube video? I will watch the video if anyone makes a decent one. Ron Beauforts tutorial on PID was very helpful back at the start as an intro to PID. As I became comfortable with first order ODE's and basic calculus, the examples on the Control Guru's website which I recreated in Matlab cemented in the basics of fundamental PID control.
  Reply With Quote
Old April 20th, 2017, 07:23 AM   #6
AustralIan
Member
United Kingdom

AustralIan is offline
 
Join Date: Jan 2013
Location: UK
Posts: 417
I wonder, will mass online courses like the udacity robotics nano degree videos be any good?

I am a big fan of open source education, so free youtube videos would be much more exciting.

I am thinking maybe OSCAT could branch out from function blocks to open source control system education. Have people do videos like the one mentioned above by Peter. Have people write textbooks. Peer review them, like a normal textbook. Have scheduled classes and let the students discuss the work on plctalk.net etc.

Dream big, Peter! Thank you for helping to educate our profession.
  Reply With Quote
Old April 20th, 2017, 09:33 AM   #7
Mispeld
Member
United States

Mispeld is offline
 
Join Date: Feb 2017
Location: VA
Posts: 100
I guess I will wade in here with my opinion that closed-loop, continuous feedback control is just plain difficult to do well, compared with other controls-related workload. The underlying theory, even with simplified models, requires somewhat advanced mathematics. Though, I will be quick to add that a complete understanding of the theory is not necessary for success in specific fields such as industrial process control, which is the context for the remainder of this comment.

With classical PID as a control strategy, you are dealing with an implementation step followed by a tuning step. The implementation is typically a hardware device (e.g., single-loop controller) or programming a PID function within a larger control system. There are many details that need to be correct if the PID is going to work well, such as input scaling, output scaling, update timing, etc. In most cases there is basically a correct set-up based on the devices involved and to some extent the process under control.

The real challenge comes with tuning. Part of this challenge is inherent in the problem, and part is "self-inflicted." Inherent challenges include the process itself: is it well-behaved (linear, time invariant), or difficult (high order, dead-time, time variant)? Also inherent is that PID gives you three tuning "knobs" and typically one response. As a result there is not necessarily one best answer to this optimization problem. For example, tuning for set point changes may not be optimal for disturbance rejection.

Some of the "self-inflicted" challenges are related to the fact that there are many different implementations of PID, and this will critically affect how you calculate or adjust tuning parameters. For example, if are you dealing with Proportional Band or Proportional Gain? Very important because having an inverse relationship, increasing PB is like decreasing PG. Similarly with integral gain or repeats/min, interacting or non-interacting gains. Much of this inconsistency comes from history of transition from analog to digital implementation, industry preferences, and manufacturer preferences; and is probably not going away any time soon.

Closer-to-home self-inflicted difficulty is the tweaking we may do to a (typically programmed) PID implementation. Adding features like digital filters can often be helpful, but misapplied may create (or hide) worse problems. Adding logic that "tweaks" the loop (e.g., clamping inputs), creates non-linearities that may end up doing more harm than good.

In my experience, if you get the controller set-up and configured correctly; then take some time to understand its specific PID flavor (equation), half the battle is over. From that point you can either tune by seat-of-the-pants if you have the intuition and experience, or do some basic open-loop model testing to get into the ballpark using various published tuning recommendations.
  Reply With Quote
Old April 20th, 2017, 09:36 AM   #8
harryting
Lifetime Supporting Member
United States

harryting is offline
 
harryting's Avatar
 
Join Date: May 2002
Location: Puget Sound
Posts: 1,529
Peter, if I remember correctly, UW did a decent job with it in our control class with a matlab driven PID kit that moves water from one water column to another and we adjusted P, I, and D to see how well the water level was maintained. Not that I remember much of it anyway but..

It's like anything, unless you deal with it all the time, whatever knowledge I gained ended up to giving back to the professors.
  Reply With Quote
Old April 20th, 2017, 10:17 AM   #9
Peter Nachtwey
Member
United States

Peter Nachtwey is offline
 
Peter Nachtwey's Avatar
 
Join Date: Apr 2002
Location: Vancouver, WA, US
Posts: 6,469
Quote:
Originally Posted by doomsword View Post
How would you teach someone automation theory and show it makes sense in real life?
I have done it before but usually it is with interested college students.
I have helped a few that really wanted to learn. Others weren't interested after they got their A.

I would start by making the point that everything can be calculated.
If you are using trial and error you really don't understand.
There traditional way of teaching PID is showing what the different terms do. That is OK but what do they really do? This is where the professors usually let the students down.

Have you ever noticed that on YouTube the instructors use Matlab or Simulink? I strongly feel this is a crime. Matlab and Simulink are very good for providing answers but poor for providing understanding because they hide much of the work that needs to be done in their functions.

BTW, the controller gains place closed loop poles and zeros. I know that means nothing unless you have had the math to be fluent in Laplace transforms and differential equations.

Tweaking gains by trial and error is OK for technicians but engineering students should be taught more. The students are paying a lot of money to be in college and they should learn more than trial and error.

Go on YouTube. Watch a few PID videos and we can evaluate them.
__________________
"Living is easy with eyes closed, misunderstanding all you see...." Strawberry Fields Forever, John Lennon
  Reply With Quote
Old April 20th, 2017, 10:27 AM   #10
geniusintraining
Lifetime Supporting Member + Moderator
United States

geniusintraining is offline
 
geniusintraining's Avatar
 
Join Date: Jun 2005
Location: SC
Posts: 4,787
Quote:
Originally Posted by cardosocea View Post
There's an easy fix for that...
Agree... Peter if you made one I would watch it


Quote:
Originally Posted by Nachtwey
Tweaking gains by trial and error is OK for technicians
That works for me most of the time, if I hear another word about that magic button (auto-tune/fuzzy logic) "here just push this"

I have patience and have no problem seeing how tight I can get the range in so I like it, I take it as a challenge
__________________
www.PLCCable.com PLC Communication Cables, PLC Trainers, Fluke Meters, MicroLogix, ControlLogix, Siemens, Allen Bradley and more... all your automation needs... ((NEW)) After Market 1784-U2DHP Allen Bradley USB to DH+ and Gateways
  Reply With Quote
Old April 20th, 2017, 11:45 AM   #11
Peter Nachtwey
Member
United States

Peter Nachtwey is offline
 
Peter Nachtwey's Avatar
 
Join Date: Apr 2002
Location: Vancouver, WA, US
Posts: 6,469
Quote:
Originally Posted by geniusintraining View Post
Agree... Peter if you made one I would watch it
I have. I have my own YouTube channel called Peter Ponders PID.
https://www.youtube.com/channel/UCW-...fJrnZ0ftoaTU_w
I started making videos to cover PID in more detail than the other PID videos. I don't treat all systems the same. I have different videos for different types of systems. I related the transfer functions to real systems. This is super important. I can look at a system and tell if it is integrating or non-integrating and a rough idea where the poles are and whether they are real or complex. It is easy if you know a few tricks.

Some of my videos are jabs at other videos. The one about Root Locus is useless is one of them. An instructor made a series of Root Locus videos and in the end he still didn't show how he could control his system. What a waste of time.

The videos I have made so far require knowledge of Laplace transforms and differential equations. They are more math oriented but I show all the steps to do the calculations.

I can provide insights that other can't or don't. The instructors rarely have the field experience or have made a control product to know what is relevant and what isn't.
Also, if you guys have questions after looking at the videos I can answer them or go into more detail but I am afraid I am too mathematical. I know I am unless your math skills are current and there is the problem.

Quote:
8 hour video tuning a slow not-so linear loop?
It shouldn't take 8 hours.
Here is my video about controlling the water level in a two tank system where the pump pumps water into tank 1. Tank 1 drains through an orifice to tank 2 and tank 2 also drains through an orifice. I made the system non-linear. The tank walls are not vertical and the flow through the orifices is not linear with the tank level. I show all the math on how I update the controller gains on-the-fly. It is also where I got into some discussions about time constants that aren't time constant. This problem came from a student on LinkedIn maybe 5 years ago. He is now teaching according to his last LinkedIn update.
https://www.youtube.com/watch?v=d_twlM8VDuM
I would NOT have passed the student because he couldn't write a differential equation for his systems. He got an A from his instructor but the instructor was clueless. He wasn't even sure if the system could be controlled. Obviously he couldn't write the differential equations either.

Most on the LinkedIn forum said to just use trial and error. I objected strongly. People don't go to college to learn trial and error. The others on the forum said what I was doing was gross overkill. It is but that isn't the point. The techniques I show is what real engineers should be able to do.

Quote:
Originally Posted by Lord Kelvin
I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science, whatever the matter may be.
__________________
"Living is easy with eyes closed, misunderstanding all you see...." Strawberry Fields Forever, John Lennon
  Reply With Quote
Old April 20th, 2017, 12:07 PM   #12
geniusintraining
Lifetime Supporting Member + Moderator
United States

geniusintraining is offline
 
geniusintraining's Avatar
 
Join Date: Jun 2005
Location: SC
Posts: 4,787
Quote:
Originally Posted by Peter Nachtwey View Post
I have. I have my own YouTube channel called Peter Ponders PID.
VERY NICE!! when I have time I will watch them, looks like a good channel


Quote:
Originally Posted by Peter Nachtwey View Post
but I am afraid I am too mathematical
Yah think
__________________
www.PLCCable.com PLC Communication Cables, PLC Trainers, Fluke Meters, MicroLogix, ControlLogix, Siemens, Allen Bradley and more... all your automation needs... ((NEW)) After Market 1784-U2DHP Allen Bradley USB to DH+ and Gateways
  Reply With Quote
Old April 20th, 2017, 12:33 PM   #13
jethridge
Member
United States

jethridge is offline
 
Join Date: Apr 2015
Location: Raleigh, NC
Posts: 54
Quote:
Originally Posted by Peter Nachtwey View Post
Have you ever noticed that on YouTube the instructors use Matlab or Simulink? I strongly feel this is a crime. Matlab and Simulink are very good for providing answers but poor for providing understanding because they hide much of the work that needs to be done in their functions.
I think you make a good point in academia. The undergrad and even graduate level control courses I took never completely explained PID control. Working at OEM's, I've never seen a need to really dive into understanding it.

The overall goal for every company I've worked for has been turn a profit. Why spend engineering resources in something that doesn't bring us closer to that goal, whether directly or indirectly? If customers are satisfied and equipment operates at an acceptable level of efficiency with a quick Cohen-Coon auto-tuning AOI that feeds parameters into a PID FB, why invest more time in it? Why not focus on other features/improvements that will convert non-clients to clients and turn current clients into "apostles" that love and recommend our product?

I think it's an uphill battle with education attempting to cram more information into their engineering curriculum. There's simply too much information being stuffed down students' throats to really focus on PID. Then there's technology advancing and replacing mundane/repetitive tasks we used to perform by hand. Why waste time performing trig, long division, and solving systems of equations by hand when a device will do it faster and more accurately. Now you can invest that time into something else you can reap the benefits from.

For the argument that, "if technology was ever taken away, you'd have to do those by hand"... If technology was taken away, there would probably be more pressing issues than these hand calc's.

My worthless 0.02
  Reply With Quote
Old April 20th, 2017, 01:41 PM   #14
Doug-P
Member
United States

Doug-P is offline
 
Doug-P's Avatar
 
Join Date: Jun 2003
Location: Pa
Posts: 1,207
Quote:
Originally Posted by Peter Nachtwey View Post
I have. I have my own YouTube channel called Peter Ponders PID.
https://www.youtube.com/channel/UCW-...fJrnZ0ftoaTU_w
The linked video has only 67 views - that right there is part of the problem. With all the stuff on YT it's surprising to me that more students haven't searched, and found, material like this to augment their classroom studies.

Since there are frequent posts here about PID I think it would be worthwhile to make your channel a sticky.
__________________
Let's eat Grandma!

Let's eat, Grandma!

Words are very important, but punctuation saves lives...
  Reply With Quote
Old April 20th, 2017, 02:18 PM   #15
Peter Nachtwey
Member
United States

Peter Nachtwey is offline
 
Peter Nachtwey's Avatar
 
Join Date: Apr 2002
Location: Vancouver, WA, US
Posts: 6,469
Quote:
Originally Posted by geniusintraining View Post
Yah think
We didn't get to the moon by trial and error. Sure there was a lot of trial and error before computers but now things can be calculated or estimated fairly well.

Quote:
Originally Posted by jethridge
I think it's an uphill battle with education attempting to cram more information into their engineering curriculum.
Yes, but how much of it is useful? That is one of my gripes about colleges. They teach what has always been taught before, now what is relevant. Root locus is not relevant. With little effort one can do much better than Z-N or C-C. Z-N and C-C are not general solutions. They work poorly for temperature control. They don't work for motion control at all. Then there is the overshoot that occurs in Z-N and C-C.
Basically these methods are attempts at tuning without making the effort to understand the plant. So why do they teach this in college?
__________________
"Living is easy with eyes closed, misunderstanding all you see...." Strawberry Fields Forever, John Lennon
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
Control Logix 1756 jamalshahid LIVE PLC Questions And Answers 9 May 8th, 2012 10:24 AM
Red Lion Crimson 3.0 – Control ID in action code. Dyslexicbloke LIVE PLC Questions And Answers 0 July 19th, 2011 08:17 AM
Proportional-only control – why won’t it work right? Ron Beaufort LIVE PLC Questions And Answers 13 April 25th, 2005 04:18 AM
how often should I trigger the PID? Ron Beaufort LIVE PLC Questions And Answers 11 February 22nd, 2003 10:57 AM
grounding power sources drewcrew6 LIVE PLC Questions And Answers 18 December 12th, 2002 05:16 PM


All times are GMT -5. The time now is 08:52 PM.


.