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Ernst Dummermuth's articles in Control Design over the years reflect his considerable controls experience as a long-time Allen-Bradley/Rockwell Automation employee and independent consultant. He's been involved in advanced technology endeavors, including architecture proposals, fast prototyping, concept verification and standardization, and product development. His work yielded 42 patents and numerous publications. Dummermuth's articles proved very popular as measured by the number of page views they've tallied on our website over the years.
This month we reprise his April 2007 article, "Closed-Loop PID Algorithms in Motion/Motor Control."
I also came across a November 2003 discussion about terminal block choices in the department we then called The Answer to Your Problems — now called Real Answers. We're rerunning it as originally published, starting on p50, because it's a pretty timeless piece about the technology choices available.
It also reminded me of the first time we poked that hornet's nest, with a December 1998/January 1999 article about choosing the right terminal block for your application ("Choosing Terminal Blocks"), and we found ourselves in the midst of heated disagreements over the merits of screw-clamp vs. spring-clamp, and NEMA vs. IEC. IDC technology hadn't really entered the North American skirmish at that point.
Here's a sample of the tone: A Rockwell Automation product manager says spring clamps are superior when vibration is a concern. "They're more secure than screw clamps, which can be lifted out by vibration, where the [spring] clamp cannot," he explains. "Others may say that the screw is better, but our testing indicates otherwise. These tests were done to meet the very stringent vibration requirements of submarine standards and UL 'pull-out force' requirements."
Dissenters say screw clamps are superior in high-vibration environments — it just has to be the right screw clamp. "Some manufacturers just use an extruded box-type clamp and tap and thread a hole — that's the least expensive way," explains a product engineer from [what was then] PLC Direct. When using these terminal blocks, the screw can vibrate loose, especially during shipping or in a rugged environment. To prevent loosening, manufacturers use various locking mechanisms that act like a lock washer on the screw. "You can get about 30 times more force with a screw clamp," he argues. "In most rugged industrial environments, I don't see many spring clamps. They're not seen as very rugged."
And so it went. And so it goes today, for that matter.