Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Tank Level Control

Tank Level Control

Tank Level Control

If I were teaching I would use this example. I got it from a student that was posting this problem on LinkedIn. Most of the forum had different opinions as to whether the system was controllable. Even the student's instructor had doubts. The system consisted of two tanks and a pump. Each tank had a level feed back. The pump pumped water into tank 1. Tank 1 had a hole, orifice or fixed valve on the bottom that allowed water to flow into tank 2. Tank 2 had a similar hole, orifice or fixed valve on the bottom. The goal was to control the level in tank 2. To me it was obvious that the level in tank 2 could be controlled. One could look at the system as two low pass filters in series but there are a few "gotchas". Much of the forum suggested many ways of tweaking on PID gains. I chastised the forum because one doesn't go to college just to learn how to tweak gains. Monkeys could do that given enough time. People go to college to learn how to design systems. In this case one should go to college to learn how to be a designer, not simply one who commissions a system that is already built. After all, how does one chose the size of the pumps, orifices or valve, shape and height of the tanks? Nothing is learned by just tweaking gains and drinking coffee while watching the results.

The student got an 'A' but I wouldn't have given him one. I wouldn't have even given him a passing grade because he could not define his system. He did manage to control the level in the second tank by trial and error.

In my experience there are plant engineers that just keep things running. The next level is system integrators/OEMs. Finally there are the designers. Even among the designers I have 3 categories. There are those that kludge systems and hope they work, those that evolve systems, and then there are those that are golden that design and model their systems. These are the same engineers that design air craft, space craft or other things where learning by trial and error is not acceptable.

So below is a video for my solution to the problem. I do not assume anything is linear in the end. Gains are calculated on-the-fly. No system identification is required. From the differential equations it is possible to simulate the system with all its non-linearities. Too many so called engineers say the system is non-linear and throw up their hands and just tweak gains until they get an acceptable response but isn't what one should learn in college.
Here is my solution.
By now is should be obvious that I like to use differential equations. I do NOT see differential equations used in control books, just Laplace transforms and matrices and they are given. The students are paying too much money. The students are being cheated.

OK, I admit, I made a mountain out of a mole hill but it is one heck of a mole hill. In the end it is not the mole hill that matters but how one approaches problems.

I forgot to mention. NO Root Locus required.

Peter Nachtwey
Delta Computer Systems

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close