The Importance of Fundamentals

Summary

It is hard to believe that I recently surpassed 30 years in the automation business. In the early 1990s, when I started my journey as a co-op student, I was handed a pile of drawings, a couple of documents and a book on how to program an Allen-Bradley PLC5. It has been an awesome ride since then.

As our world grows more connected, vendors want us to connect their devices directly to our control systems, and others want us to move control out to the edge of our networks. I am not sold on this being a good thing, because automation systems do not handle chaos. The automation programmer usually does not have enough time or background to properly account for every abnormal condition the automation system may face.

These new technologies are exponentially increasing the complexity of our systems without addressing the people who must maintain them. End users are looking for ways to keep things simple and broaden the resource pool that can work for them. A core issue is that we seem to have lost our connection with the automation fundamentals. We can barely maintain what we have and, in many cases, have already lost the battle as workers age out. Even if they are replaced, there is no mentoring or job training program for the new resource. Let us get back to the core principles that make automation systems work.

Start at the beginning

Fundamentally, an automation system is just a bunch of computers talking to each other with ones and zeros. Programmable logic controllers (PLCs) and control programs running on computers are deterministic. “IF” this “AND” that, “THEN” do this “ELSE” do that. A human must work through scenarios and then program all of them into the control system so it can react. Process definition is required for the programmer. Remember the old term “garbage in, garbage out.” It does not matter how well you program the system if the mechanical design is junk. Because one can never plan for every scenario, limiting the number of abnormal situations may be better than trying to account for all of them.

I remember troubleshooting a large data highway protocol (DH/DH+) with more than 20 PLC5s, five PLC3s and a couple of 1774s communicating with each other. The network was slow and unreliable, not performing close to its design parameters. I was a co-op student tasked with figuring it out. The Rockwell Automation technician showed up with an oscilloscope and far less knowledge about the data highway protocol than I had. He brought a book containing a wealth of information about what we should expect to see on the oscilloscope for the different speeds it could run. I learned so much that afternoon. I figured out the oscilloscope and, in a matter of minutes, made several astonishing findings that we quickly corrected to restore the network to its design performance. This started me on my path of learning about the difference between the theoretical and the practical, the office and the field.

One night I was called into a plant after the production train had been down for several hours because they could not establish flow. The maintenance team had tried everything: forcing inputs, changing code and restarting the train several times. The human-machine interface (HMI) screen showed that all the valves were in the correct position, but still no flow. After listening to what had transpired, I asked if anyone had walked the line yet to see what was happening. Because the train runs every 40 minutes, no one expected anything physical to have changed.

As we opened the door to the production area, we immediately saw that one of the actuators had fallen off the valve, but the air and electrical connections were still connected. The actuator was doing what it was supposed to, but it was no longer attached to the valve body. The team was so focused on the problem being a programming issue that they lost the ability to look beyond it. We must strive not to make assumptions like this. If it worked fine before you made changes and it does not work now, it is highly likely that your changes are affecting it. You missed something and made an incorrect assumption. It is, again, time to get back to basics.

The problem with assumptions

Every decision you make and keystroke you perform in developing a control system comes with many assumptions. How have you validated those assumptions? Are you qualified to make those assumptions? Do you have enough information to make those assumptions? A common issue I often run into is being asked to control something very tightly, but the measurement device cannot provide a value at the same resolution. You may have heard this as “controlling with a micrometer but measuring with a yardstick.”

Do you have enough information or knowledge to know the resolution of your measuring device and the abilities of the controlling device? How about the process? Can it be controlled at the resolution the user is asking for? If the desired control is one-quarter-inch but the device can only measure to a half-inch, what should my expectations be about how well I can control the process (Figure 1)?

As more systems are implemented, we are quickly moving away from ac circuits to dc circuits. One thing about ac circuits is you do not have to worry about polarity. In dc circuits, polarity is critical. Even how you measure the circuit with your multimeter is important.

While drafting this article, I had the opportunity to troubleshoot a 600 Vdc short circuit on a label machine. I had to relearn a few of the basics that I had not used in a long time. For example, when measuring a dc circuit, you must maintain polarity on your meter connections to the circuit. I had forgotten that, and the readings I was getting did not make sense. In one case, this led us down the wrong path and wasted valuable time. To understand why this is, you must understand how the components of electronics work (transistors, capacitors, diodes, etc.). Without understanding how these devices work, a lot of energy, money and downtime is spent arriving at incorrect conclusions and replacing many good components to stumble across the one that failed.

Four foundational concepts

Automation professionals should have many core foundational concepts committed to memory. The basics like Ohms law, numbering systems, signal conversions and others are critical to us being successful in our profession. Knowing and understanding foundational concepts will make you a far better control engineer and system programmer, not to mention a much safer person in the field and an expert troubleshooter.

I recommend every automation professional understand these four concepts related to instrumentation and measurements:

1. How a field instrument converts the physical thing it measured to an electronic signal for the controller to use.

2. The opposite of No. 1: How a controller converts the electronic signal to a physical action.

3. The equations used in instrumentation scaling and the potential errors that can enter our systems (such as those for zero and span error, as represented in Figure 2)

4. The different numbering systems available to you (such as octal, decimal and hexadecimal, as shown in Figure 3)

What to know

As automation professionals, we must never lose sight of a critical distinction between our work and the work of other programmers and technology professionals: Our work controls things in the field. Our work makes things move, potentially putting people, equipment and products in dangerous situations that we did not intend. So, knowing the basics is essential to both operation and safety.

Understand fundamental properties that convert code into physical movement: volts, amps, ohms and direct current (dc) and the concept of alternating current (ac). Know that ac requires a different approach when using troubleshooting techniques, and one must understand the readings you get on your test equipment. Understanding ac behaviors is essential as most of our modern world uses these behaviors to run industry, to provide information, for medical therapies and more. To understand ac is to understand the why of modern technology.

Our programs have become bloated and inefficient because memory is cheap and processor speeds are incredibly fast. Knowing the appropriate use of different data types is a foundation of well-written and efficient programs.

To be a great automation professional, you also must know the tools of the trade. Know how to use basic tools, such as multimeters and oscilloscopes, what to anticipate in the measurements and how to correct the errors.

Modern electronic industrial devices are increasingly digital; features provided through software can make a more efficient and scalable networked device that is useful in different environments. While most systems communicate in digital format, the measurements made in industry operate in a continuous or analog world. For the digital device to communicate and control, analog-to-digital (A/D) and digital-to-analog (D/A) conversions are necessary. There are different methods for performing either type of conversion. Know and understand those methods so you will be prepared for the time you work on the systems.

Make the numbers count

Understanding the various numbering systems and data types used in a controller’s memory is another important part of our work and one of my favorite topics. It is unfortunate that today’s technology creates an environment in which programmers do not have to be efficient.

Processing technology has improved so much that we do not need to worry about efficient programming and how much scan time one instruction uses over another. Different data types, such as double integers versus a float, and how much memory each tag uses are important. Our programs have become bloated and inefficient because memory is cheap and processor speeds are incredibly fast. Knowing the appropriate use of binary, decimal, integer and double integer data types is a foundation of well-written, elegantly simple and efficient programs that are easy to troubleshoot.

It is also critical to understand logic. The core of any automation program is to know the rules of logic. Understanding AND, OR, NOR and truth tables is key to not only writing PLC programs but also to writing the functional documentation used to define the process that the program controls (such as the NAND gate and logic map shown in Figure 4).

Final thoughts

After more than 30 years of continuous learning about new technologies and devices and how they fit—or do not fit—into process automation, the one lesson that I want to pass on to every automation professional is to learn and understand the basics. It will make your job easier. It will make the systems you design or create programs for more efficient and easier to troubleshoot, which will increase throughput and profit and reduce waste and downtime.

The value you return to your clients and employers will be exponentially greater when you address problems using the fundamentals.

Core principles from author and educator Larry Thompson

In January 2020, ISA and the world of automation and control lost a passionate and dedicated innovator, educator and author, as well as a funny, kind and caring man of great faith. Larry Thompson was dedicated to helping others succeed and expanding the profession. He was also the author of Basic Electricity and Electronics for Control.

This student-centered, two-book set focuses on practical applications and provides exercises that simulate real-world applications. The book begins by reviewing the basics, including how to use digital and analog meters, bridges, power supplies, solidstate circuitry, oscilloscopes and analog-to-digital converters. It expands to more advanced topics, such as understanding how transistors work and their practical application in operational amplifiers. The workbook contains a series of real-world labs so readers can immediately apply the lessons learned.

The principles in this book are core to the automation profession. Even though the original version of the book was written when programmable controllers were just starting, the principles of how devices work have not changed.

Throughout his distinguished career, Thompson was a technician, technical trainer and course developer in electronics, measurement/control and computer networking. He was a Certified Automation Professional (CAP) who served as an adjunct instructor for ISA for more than 35 years. He wrote several books, including ISA’s Industrial Data Communication.

Thompson was a longtime automation professional and owner/general manager of ESdat Co. (Electronic Systems: Development and Training Company), a consulting firm specializing in industrial data communications. A 20-year veteran of the U.S. Air Force, Thompson specialized in maintaining electronic encryption equipment during his service. His postmilitary industrial experience included test engineering supervisor for numerous companies and department chair for E-Commerce Technology at Texas State Technical College.

Thompson’s legacy will continue as those he taught share their knowledge with the next generation of automation professionals, and the books he authored continue to be essential resources. I hope you enjoy the book and workbook as much as I enjoyed supporting the revision.

_{This feature originally appeared in the February 2024 issue of InTech digital magazine.}