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A tell-tale sign of good content is the handling of how a three-wire control circuit is built in a PLC. Embedded Intelligence columnist Jeremy Pollard, CET, reports that he finds the book's explanation confusing, although accurate.

Jeremy Pollard, CETBy Jeremy Pollard, CET, Columnist

 

My editor asked me to review Programmable Logic Controllers, 4th Edition, a book by William Bolton, author of college texts in engineering and other technical subjects, and published by Elsevier.

The book has been on engineering book shelves for 10 years now, and with a 4th edition, one has to wonder what more can be said. I looked at this book first from the point of view of a rookie entering today’s controls environment, which seems to be its audience target. I also looked at the content for relevance to someone who has been in the biz for 10 years or so. Does this book offer anything for them?

I taught with Rockwell Automation for more than five years, and have been teaching PLC instruction for more than 25 years. If anything is clear, when comparing this book to the BTEC syllabus from Edexcel that was the basis of what I delivered in Level 1 and Level 2 courses back in the `80s, it’s that not much has changed.

The book’s primary additions include safety instruction and IEC-61131 coverage.

PLC basics have been written about many, many times, and Bolton does a good job of presenting what a PLC is and does. He uses examples from various manufacturers, but I would have preferred his drawings to be a bit more informative and clear. Scanned images just don’t cut it these days.

He spends a lot of time on input and output devices, which is very cool for those who might be wading into this pool for the first time. He deals with digital and analog devices, and does a good job with them. Pictures would be nice though, since a newbie might not know exactly what these devices look like.

Hydraulics with a few fundamentals is included, which is good for anyone interfacing with certain machine control applications. Examples aid the reader in understanding how some of these devices are used.

I’ve always thought numbering systems was the hardest thing to teach someone, and the author treats this subject with clinical style—there just isn’t any other way.

The basics of any PLC are covered well, such as I/O scan, hardware (very specific to each vendor), and some basic communications issues.

He talks about the MAP protocol. I have to wonder why.

In the past 25 years we should have migrated from normally open and normally closed to describe logic instructions. Apparently not here. I think it doesn’t allow a rookie, who probably has more experience in the computer world, to think outside the relay/electrician box.

A tell-tale sign of good content is in the handling of how a three-wire control circuit is built in a PLC. Sorry to report that I find the explanation confusing, although accurate. The author uses the term switch for both a PLC instruction as well as the hardwired pushbutton. That’s very confusing to the uninitiated.

His inclusion of test questions at the end of each chapter is encouraging—and, yes, there are answers to guide you.

There are sample programs as well, using the different manufacturer nomenclatures. Again, I find Bolton a little out of touch, since “F1” in any computer software is the help key—not entering offline-mode programming. He must be using ODS-based ICOM software, or 6200 series software, both of which have been out of service for a while.

The sample program documentation states that the removal of the right-hand power rail is allowable in IEC-1131. This feature was in 6200 series software due to the use of dot matrix printers, and printing the right edge took a lot of time.

I really was a bit disappointed in his handling of the IEC-61131 languages. He refers to the IEC-1131 standard as being proposed. The standard was adopted about 15 years ago, and the 61131 nomenclature has been in regular use for more than four years.

He deals with safety circuits and safety relays in a basic form, and does it pretty well. The reader will get a particularly good understanding of what not to do.

There is nothing in this book for someone with experience. For a rookie, it would be an OK read, but know that you certainly will not get everything you will need from it. Although revised in 2006, it feels very dated.

 


  About the Author
Jeremy Pollard, CET, has been writing about technology and software issues for many years. Publisher of The Software User Online, he has been involved in control system programming and training for more than 20 years. He’ll be pleased to hear from you, so e--mail him at jpollard@tsuonline.com.
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