What the ability to design or program a simple start/stop circuit says about you

The ability to design or program a simple start/stop circuit says much about both the individual and our educational system. Here's why.

By Dave Perkon, technical editor

There are many experienced and productive control designers and programmers in industry today. The companies they work for know the value of a good controls engineer. Unfortunately, there are many inexperienced engineers, such as recent college graduates or maybe the seasoned engineer who likes to hide in the corner and just do what's necessary. Some are excited to learn, and others not so much. The point is, engineers come in all types—some great, some good and some bad, as in life. At no point is this less obvious than in a job interview or more obvious than while working on a project.

As an engineer and manager, I've interviewed many controls engineers, electrical designers, programmers and CAD operators through out my 27 years in industry to design and program automated equipment. Along with all the typical interview questions, I had what I consider a basic interview task: draw a start/stop circuit. Unfortunately, only about 20% of the "experienced" control-design and programming applicants could do it. Clearly, industrial, hands-on experience is all relative, and each interview was quite the learning experience for both me and interviewee.

Perhaps I'm asking too much and shouldn't expect an experienced control designer or recent EE graduate to draw a hardwired start/stop circuit.

During the interview I simply asked, in writing, that the applicant draw a start/stop circuit ladder diagram using the following hardware: a normally open pushbutton, a normally closed pushbutton, a pilot light and a DPDT relay. I also noted the requirement was to turn on the green pilot light when the momentary start button was pressed and turn off the light when the momentary stop button was pressed. I also asked the applicant to add wire numbers, device designators and relay contact cross references.

If you want to see the circuit, let me know as it was a great test. It clearly showed experience with control design and the applicant’s attention to detail—just not many applicants showed much of either. The experienced designer forgot the wire numbers or cross references and the inexperienced designer used the eraser quite a bit, along with many other issues.

Also read: How the industry can leverage new skill sets of Generation Y

Perhaps I'm asking too much and shouldn't expect an experienced control designer or recent EE graduate to draw a hardwired start/stop circuit. If they could not draw a simple hardwired start/stop circuit, I didn't think they could program one either. However, many of the applicants, who couldn't draw it, stated on their resumes that they were experienced PLC programmers, as well. This highlighted concerns about the applicant’s ability to program a PLC step sequence.

In many cases they didn't make the connection that they were the same logical circuit—one was just hardwired and the other programmed. If they didn't know the answer, I showed them how to do it with the thought that I could develop the engineer as needed, if the candidate was interested in learning. It's clear that even with a four-year degree in engineering, the interviewees didn't have any practical experience. Examples of the problems this causes are endless, so engineering talent must be developed.

"Developing and training an engineer is a good thing although the results will vary," notes Otto Fest, president at Otek. Fest thinks the real technical education starts after graduation. "College graduates are expecting $60,000 to $100,000 per year but are not worth that without experience. Industry needs to invest two or three years’ time and effort to teach them what schools don't. And then, once trained in this hands-on work, the engineer may leave for greener pastures."

Fest does offer up what I think is an excellent solution—mandatory internships. "It works great for doctors, and it works great for German college students,” says Fest. “Maybe we can learn from that. From my experience, we need to improve the technical education of graduates. Although college is a great start, it is not enough, as real life doesn't happen in college."

Colleges in Germany, arguably the world’s top technical source, have mandatory internships. In the United States, college has more to do with the “college experience,” but in Germany it's more about the classroom and hands-on experience. Forget the dorm room, student union and the parties. To graduate in Germany, you must read, write, understand and express yourself in three languages and have three or more six-month internships in foreign countries related to your major. That sounds like an excellent way to get the technical education needed for industry.

If you don't agree, I'm good with that. However, consider the mechanical engineer who graduated at the top of his class from a leading engineering university but had no practical, hands-on experience. This intelligent engineer climbed a cooling tower under construction, in the hot sun, and spent several hours removing bolts, turning over a split washer and re-tightening the bolts because he was told the split lock washers, located under the bolts we marked, were upside down. Yes, we probably shouldn't have done this on-the-job training, but we did stop him after a few hours of hard work and he now knows what a split lock washer is, in addition to the thermal dynamics he aced in college.

Nothing beats experience. If you are an engineer and don't have the experience, go get it. Wire some control panels and design some electrical schematics. It also pays to find a mentor to help you get there.

This brings me to a future article I’ll be writing on mentoring and the mentored. A mentor benefits both young and old. As a young engineer, working with a mentor is a great opportunity to improve productivity and the results of your next control-design project. I've done both, but I would love to hear some of your comments on that subject.

None of these comments are about politics. Let’s stay away from that; they are about control design for machine builders and include a few of the many ways to "re-manufacture America." I'd like to help re-manufacture America and hope industry does, also. If you cannot get it built in the United States, where are you going to go? My least favorite, but a popular option for others, is to go to China. They happen to be copying, which they are good at, the German educational requirements and flooding the world with technical students. Seems like the smart thing to do.

Do you know how to start/stop?

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Main image courtesy of phasinphoto at FreeDigitalPhotos.net


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  • <p>Great one Dave, and so true. Its all about balance, time, education (theory/practical app) and experience. But in your test subject's defence, if an industrial engineer found him/herself writing SCADA source code for the last 10 years, I would not expect them to pass your test either. (May have been taught in school, but never used in out in the real world. Use or lose it factor) for those you test straight out of school, doesn't surprise me, we see the same thing with PLC education delivered in college, it's not PLC training teach practical application skills.</p> <p>Your test in our PLC training world is similar to a smart student learning how to do PLC programming in college, only to find out in the real world, they do not know how to connect with the PLC so they can use that knowledge they gained in college. (or not knowing how to troubleshoot a communication driver, etc.)</p> <p>Basically what is occurring is we send our young to a college which by definition is "An institution of higher learning that grants the degree in liberal arts or science or both." ... But expect out of it "technical or professional training" which is not what college was conceived for. </p> <p>Underpinning the problem of an ancient greece educational system being used now days when we have technology, global market, etc., is society quit distinguishing between the words education and training. Employers are expecting college students to come out of the educational institutions trained, but that is not what colleges traditionally were designed for. Supply and demand is slowly changing that, while people continue to use "education" and "training" interchangeably. :)</p>


  • <p>I think this article hits tons of points right on the head. I am one of the very few younger generation Controls Engineers. I did a mandatory co-op in college (3 full-time semesters). My co-op was a controls engineering position although I couldn't get my school to accept our PLC course as one of the required electives for my degree. Only the mechanical engineers could use it as an elective. Aside from basic circuit laws and binary, the rest of my education did not directly relate to what I do for a living. However, the rest of it did indirectly give me a deeper understanding to the "behind the scenes" of what I do now.</p> <p>I was very lucky to be mentored the way that I was in my co-op. I was even luckier to find employment under other great mentors. I think my education combined with my experience being mentored have turned me into somewhat of a double edged sword in a market that is full of electricians-turned-controls engineers who are still using Windows XP and refuse to learn how to use the middle mouse button and college graduates who have never operated a machine before. </p> <p>I have faced a lot of resistance mostly from the copy and paste engineer who does it the way he has always done it because that is the way it has always been and it works. However, I have had great success with the too-few-and-far-between open-minded mentors who aren't threatened by being questioned. These mentors have made me the success that I am and I believe that my mentors would agree that they have benefited from my constant questioning and newer way of looking at things. </p> <p>Btw, I did draw up a little start/stop circuit. It is silly how something so simple can be so intimidating when asked on the spot. I remember my first mentor told me that he used to ask people to draw out the logic for a simple cylinder motion during interviews. He was also amazed at how many people could not do it. He then went on to show me how he thinks it should be done as well as the pros and cons to the other variations that have led him to his way. From then on, I've always had a hunger to learn the fundamentals and keep them close in mind.</p>


  • <p>Hi Don, thanks for your comments. You made some great points and had me thinking about my current issue--teaching my daughter to drive. She easily passed the test to get a permit, but she needs to develop the skill and experience. It drives home the point that internships are needed as a part of college. The young drives can be expensive.</p>


  • <p>Hi Tisha, I enjoyed your comments. I also had some great mentors at my first job out of college. I had little experience, but they got me up and running quickly. Thanks Bill and Jim!</p> <p>It's great that you are pushing past the old-school and old-fashioned guys. I'll gently question and ignore those guys with you. Embrace the new technology, define a new tradition and be sure to mentor someone along the way. You know how to start/stop. Enjoy.</p>


  • Funny. Applying for a drafting job while working my way through college, I was asked to explain that circuit. I did. Got the job. It was 1966.


  • I love it. And I'm sure that 50 years from now, it will still be important to know how to start and stop.


  • Dave, I'm at the 25+ year point of a Controls Engineering career and drew out a stop/start circuit in about 2 minutes, including the time to grab a piece of paper. One thing stumped me, though--and not for the usual reasons. I favor compact, self-evident design and have been using a single-line Start/Stop circuit for years. Without adding a PLC input or something driven by the MCR, I don't have any cross-references to complete the exercise with! This is a particularly memorable concept for me because designing a Start/Stop circuit was my first crossover from being a Mechanical Engineer (my degree) to an Electrical Engineer (my profession by practice). The stress level of doing this in an interview would definitely make it more challenging, though. I once asked two programmers I interviewed to design a heartbeat circuit between PLC's. One couldn't do it, the other created something that worked, but was overly complex. The simplest solution is for one PLC to turn it on if it's off and the other to turn it off if it's on. --] / [------------------( )--- --] [------------------( U )---


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