Manufacturing AUTOMATION

What’s old is new again

June 13, 2013
By Jeremy Pollard

This isn’t a software column as such. But it is.

I had just finished writing a four-part series on technology and the effects on our economy when, suddenly, a thought struck me.

We have been using PLCs for 40+ years. There are tons of things that have changed and some things that haven’t. Any PLC or PAC is doing the same job as it did years ago, but now it’s for a different reason—business.

The business of technology used to be fun. In my last column, I talked about the Raspberry PI and how much fun it’s going to be to get back into a bit of banging mode. So far it’s not all that much fun because I am realizing that I am far behind the curve.


I grew up with PLCs, as did most people my age in my industry. The changes that occurred were phenomenal. We went from a relay-replacement expensive slow appliance to a compact, fast, “I can do anything” device/node.

Before laptops, the industry used definite purpose devices for interfacing. Remember that, all along, PLCs used a programming language—you just needed a device to enter it.

There are varying accounts about how stuff got started, but Dick Morley and his company Modicon (Bedford Associates at the time) created a technology appliance that could do what the big boys were asking: replace relays. The technology was sold on troubleshooting and the fact that anyone in your maintenance department who knows relay logic can program and work with PLCs.


The language to program them was ladder logic, the same representation that an electrician has seen for years on D-size drawings.

In the ‘90s there were individual software companies popping up everywhere. But after so many years and permutations and false starts on successors, the PLC (and its ladder logic) is still the king.

Morley wrote in the mid ‘90s that ladder logic will erode in time. Seems it hasn’t. It works—plain and simple.

There are more than 200 vendors of PLC hardware. Not one of them offers a non-ladder programming solution.

Remember fuzzy logic? Today, it’s nowhere to be found.

So here we are. Companies are delivering solutions with PCs, dedicated hardware, fancy screens and a full array of options. You can even connect to your nuclear controller over the Internet!


But the one consistent theme in all of this is ladder logic. It’s simple, robust, extendable and, having learned it, it provides a career that may more sustainable than most, or at least some.

What’s old is new again

This article originally appeared in the June 2013 issue of Manufacturing AUTOMATION.

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