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12/27/2017 2:42:00 PM
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Relays rock
I am all with you on relays. If their duty cycle is anything reasonable as it is in HVAC, they last a long time and the isolation is complete.

I service industrial equipment and much of it is old, It is old because it does the job and the cost is already fully paid.  The cost of replacement is often extreme, in hundreds of thousands of dollars, and there are training, interface and operational differences to be overcome.

Out in my world and that of my customers, the latest is usually overpriced, overfeatured and different enouigh to make things difficult for my customers.  Service for these brand new darlings is a several hundred dollar service call to say, "It's broke, buy an entire new unit as they are not repairable, $5000 please."

In terms of assumptions, a line of CNC machines made in Italy uses green which means frame ground in the rest of the world for +24 volts. And all the services docs are in the German (which I studied 40 years ago) and Italian (which I never did study.)

In another product line, remote controls, the mounting frame is ground, sort of, so long as the mounting posts that hold the circuit board up in the case are tight, otherwise it is not. Thke unit is dingy and borderline to begin with, so it doesn't need any hellp from intermittent operation.  This particular company started in Sothern California, was bouight out by another company in Pennsylvania that tried to kill the line and replace it with their own shoddy line. It is turn was bought out by an English comgomerate. The docs on the old unit and all the parts went in the dumpster when they moved out of California.

Remember young engineer that your product will go out in the cold cruel world that will appreciate not your cleverness or saving 2 cents on that borderline resistor, but that their assembly line doesn't shut down costing them $1000/hour so you could save the 2 cents per unit on your $50,000 product.


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