“Mastering Cascade Control” has been released by PIDTutor. The book is designed to help technicians and engineers to implement and troubleshoot split-range control applications.

Cascade control uses two controllers with a single control valve to provide faster, more accurate control response to upsets. Cascade control can be used for many different applications, such as heat exchangers, tank levels, and distillation column control. Cascade control is widely used in the process industries, such as pulp and paper, oil and petrochemicals, and mining.

George Buckbee, President of PIDTutor, and author of the book, says: “I have spent most of my career in manufacturing plants. This is a practical book for plant technicians and engineers, using straightforward rules and guidelines, without the complex math.”

“Mastering Cascade Control” covers all aspects of the use of cascade control. Starting with the basics, the book discusses when to use cascade and when to avoid it, costs and benefits of cascade, how to configure the control strategy, how to commission the system, tune the loops, and even how to train operators and troubleshoot problems. Color illustrations simplify the key concepts.

“Mastering Cascade Control” is available on-line via the PIDTutor web site, or via Amazon’s CreateSpace at https://www.createspace.com/3431286 .

Teenagers know what is “cool”. And this week I have two teenage votes in the cool column for the PID control algorithm on the Segway Human Transporter. Well…almost! This week, I took a family vacation to California. It was great to get away from the cold, wind, and snow of Pennsylvania. My two teenage sons and I decided to take a Segway tour of San Francisco, with San Francisco Segway Tours.

If you haven’t seen one, a Segway is a two-wheeled scooter-like device that somehow manages to stand upright, go forward and reverse, and turn tight zero-radius circles. You can find pictures and product info on http://www.segway.com/

After a short training session, we followed our tour guide for a 2+ hour tour of San Francisco. We went up and down hills, through North Beach, past many San Francisco landmarks, and finally out onto the piers near San Francisco Bay. At a top speed of about 10 miles per hour, it was a lot more efficient and less tiring than walking. It was a sunny day, and the sight-seeing was great. But that’s not the best of it…

The controls are actually the cool part. The Segway has mini gyroscope-like devices to measure the angles and the angular momentum of the Segway (and its passenger). The controller moves the two wheels to keep you upright. When you first step up onto the platform, and it feels for a second like you will thrown off. This is because your own system is fighting the Segway to keep you upright. Just relax, and in 5 seconds, you are standing upright, balanced by the machine.

Lean slightly forward, and the machine glides forward. Shift back toward your heels, and it stops. Even though you are only on two wheels, you remain perfectly upright. The angle is being controlled by a PID algorithm, execution 100 times per second, making minute adjustments to the two motors.

There is great article on the Segway available on How Stuff Works. Check it out if you want more details.

In just a few minutes of riding time, the Segway seems completely natural. You don’t even have to think about starting and stopping. You body adapts to the weight shifts pretty easily. In a couple of hours, we covered most of downtown San Francisco, including Lombard Street (not the steep part!), Coit Tower, North Beach, Fisherman’s Wharf, and Ghirardelli Square.

As we finished our trip, zooming around a concrete pier that juts into San Francisco Bay, I couldn’t resist being the “nerdy dad”. I had to explain to my sons how this contraption works. Believe it or not, they actually thought that PID was “cool”!

Call me old-fashioned. I have always been a fan of real books. I simply cannot read an on-line article of more than two pages before I start clicking on something else. Yet I can sit down and read through a good paperback from page one through three hundred. I love the feel of a book, the smell of it, the satisfied “thump” when I close a hardcover after finishing it.

What does this have to do with process control? Well, we seem to be in a prolonged world-wide movement away from the “real” world, and into the “virtual” world. It’s not just books. Audio has moved from real vinyl (The grooves actually show the music!) to CD to the virtual iTunes. A walk in the woods has been replaced by Discovery Channel in HD. And control system vendors are actively seeking to create more and more “Virtual Plants”, for training, and even operation.

But we have to be very careful about this. The Virtual Plant will never be as good as the real plant. As my friend Ben Weinstein taught me “All models are wrong. Some are useful.” Models can never tell you as much as the real plant.

As a young engineer, I spent months training with maintenance technicians and operators who knew how to listen to the real plant. Even as we implemented DCS systems, they insisted on routine walk-arounds through the process. Why? Because they could employ all of their senses.

These people didn’t just look at the video screen. They listened to the hum of the equipment. They felt the vibration of the floor. They listened to motors by holding the handle of a screwdriver to their ear, and touching the blade to the motor. They actively smelled all parts of the process. (OK, so that wasn’t always my favorite part!)

And from all of this sensual, tactile experience, they learned about how the process was behaving. They could immediately identify when something was not quite right. They could measure things for which there was no instrument.

I like technology, I really do. And there have been tremendous strides in modeling, simulation, and the creation of virtual plant worlds. But we should always try to become better process control gurus. And a great way to do that is to get out of the control room, and walk around in the real plant. Pay attention. Listen to the frequencies in the hum. Look closely at things. Feel the floor vibrate. You will be surprised at what you can learn in the real world.

Never forget that all virtual worlds are based on models, and “Models are always wrong!”


Thanks to Nancy Bartles from Control Magazine, for posting a link to this insightful blog post, which was the inspiration for this post.

Control Valves are the workhorses of the process control field. As a process control guru, you should know how to select valves for all sorts of process conditions.

One of the most important resources you can have for control valve selection is the Emerson (formerly Fisher) Control Valve Handbook.

This is an incredible resource.  A complete copy of the famed Fisher Control Valve Handbook, the “Little Black Book” of Control Engineers, almost 300 pages, on-line, for free!

Click here to download the Fisher Valve Book as a pdf file

If you are new to the topic of selecting control valves, I would also recommend a series of articles by Béla Lipták. With 50+ years in the process control industry, Mr. Lipták knows his valves. This 3-part series was published in Control magazine in 2006:

Click here for part 1

Click here for part 2

Click here for part 3

This 3-part series should bring you up to speed, and help you to make an informed selection.

Do you have other great resources to suggest? Leave a comment for this post.

OK, so you want to be a process control guru. Can you explain your job in one sentence?

Not so easy, is it? Try explaining it to your Mom, or your Grandma, or your neighbor, grocer, or kid’s basketball coach. You might say something like “I work in the automation of process plants, like oil refineries, paper plants, and chemical plants.” That still doesn’t really explain what you DO. Trying to explain it in any level of detail, and you’ll have to explain HMIs, PIDs, PLCs, DCSs, and a host of other TLAs (Three-Letter Acronyms..ha ha).

It is simply a fact that our industry has a lot of jargon. To the layman, it can seem like we are talking another language. “We’re using fieldbus, so we upgraded to Smart IO, but our DCS HMI can’t show the diagnostics, so maybe we should have stayed with 4 to 20 milli-amps.” You get a puzzled look from operators, managers, and even engineers from other fields. How can we combat this problem?

When I first started as a control engineer, DCSs were “the new thing”, and they weren’t well-understood. I began to think of myself as a ‘translator’. I spent a good deal of my time explaining to managers and operators. They wanted to know about costs and benefits of DCSs. They also wanted to know how they worked, why they would be reliable, and so on. I had to find ways of explaining new concepts (even “network” was a relatively new term to many). The more they knew, the easier it was for me to do my “real job”, actually implementing the DCS systems.

Explaining ourselves does not always come naturally to we engineers. We draw on a different base of experience than “lay people”, and we can come across as arrogant if we over-explain. So it is a good idea to practice how we communicate. Here are some suggestions for how we can practice explaining ourselves:

1. Explain your job to a 5-year-old.
2. Explain your job to a grandparent, or someone who doesn’t use computers.
3. Practice an “elevator speech”. Imagine you have 30 seconds to convince your boss’s boss to fund your next big project. What would you say? Now, practice it. Really. Say it out loud. Time yourself. Don’t waste a single word.
4. Try to explain something complicated in a simple picture. Try “ratio control”, or “feedforward”. You are limited to a half a sheet of paper, or one napkin. No more than 5 written words allowed.

These are just some practice exercises to help you develop your ability to get your point across quickly, and simply, without drifting back into “control engineer language.” Good luck with it.

By the way, here’s a cool example of visual communication from a mathematician:

I recently saw the movie “Avatar”, with all its 3-D graphical splendor, and an idealized world of happy people communing with nature on the forest-world of Pandora. Knowing that practically the entire movie was computer-generated, I was reminded of the role that simulation plays for process control.

In an effort to be a better process control guru, we should all make an attempt to understand how things “should” work. And for that, simulation is a terrific tool. There are many types of simulation tools available, and you should choose one that fits your specific needs.

First, decide if you need a static or dynamic simulator. Static simulators handle steady-state conditions, and can sometimes be accomplished within an Excel spreadsheet. But most control problems will require you to deal with dynamics. This will enable you to study how controllers respond to changes and manage to get the process in control over time. Here’s a link to a simple dynamic simulator: http://www.simapp.com/simulation-software-description.php

Next, you can determine if you are going to develop your own process models, or if you need pre-defined models for complex processes, like distillation columns. For years, students have been developing their own models using software like MATLAB. Industrial versions of MATLAB adds more pre-configured simulation object libraries.

The next step is to determine if you need the simulator to include a physical properties database. With this feature, the simulation can automatically determine boiling points and even chemical reactions without special programming on your part.

Lastly, determine whether the simulation will run stand-alone, or if you need it to connect to something in real-time. The latest trend in simulations for operator training is to connect the simulation to a “virtual control room”, allowing the operator to practice on your simulated plant, using an HMI that looks exactly like the real plant.

As you add complexity and fidelity to a simulation, the cost can rise dramatically. A simulation of a full plant, integrated to HMI, with training materials can reach the $1 million mark. With such a simulation, operators can be trained to face both normal and abnormal operating conditions, reducing the risk of errors in the “real” plant.

Just like in Avatar, a good simulation starts to blur the lines with reality, eventually mimicking the real world with such accuracy that it can be hard to tell the difference. In the end, here’s my advice: every process control engineer should do SOME simulation. Whether you are building a high-tech operator training room, or simply predicting a control loop’s recovery time, simulations can provide a better picture of how the world “should” be.

I spend a lot of time helping clients to save energy in large-scale industrial plants. It’s not every day that those process control skills come in handy at home. But I’ve found a great tool…

I have installed a “whole-house electricity monitor”. This consists of two clamp-on ammeters, a transmitter and a monitor. The ammeters and transmitter go inside your electrical supply panel. I keep the monitor in my kitchen.

Basically, this device shows my real-time electricity consumption. After I input my electric billing rates, it even shows me instantaneous cost per hour for electric use. So I now know how much it costs to leave a light on (about $0.01 per hour), and how much the electric heater in the family room costs ($0.40 per hour). Knowing this info is useful, but the big benefit comes from knowing your baseline consumption, and recognizing when things are not normal.

I have three teenagers. They leave a lot of things turned on when they are not using them. But now, looking at my monitor, I can tell when things are left on. And yes, I can harass them to save some energy. But I have found that I can generate the most savings by simply paying attention to the power usage at certain key times:
* When leaving the house for the day.
* Before going to bed at night.
* Before leaving town for a trip to Grandma’s

After 3 months with the monitor, my results are in: 30% savings compared against the same months a year ago! That’s pretty significant for me, since I have electric baseboard heat as my primary heat source. I expect to save over $600 this winter. That’s personal, real, after-tax savings.

How much did it cost me? About $75. The monitor I use is called “The Energy Detective”, or TED. You can find it on-line here: http://www.theenergydetective.com/index.html . No, I don’t get a commission.

If you’re comfortable working with your home electrical wiring, it is pretty easy to install. Out of your comfort zone…call an electrician. It only takes about 20 minutes to install.

It’s very satisfying to be saving so much on energy costs. The kids are even paying attention on their own now…they’ll call me when the meter shows high usage. If you have a high electricity bill, this is a great way to start saving money. Good Luck!