I did not regard any of the situations that I encountered using optical isolated relays as a drawback. They never gave me any problems, with one small exception. A solid state relay that controlled s solenoid valve had one of it's twi anti-parallel SCR devices fail open. So the indicator light would show that the output was active but the valve would not shift. Once I realized that the bulb was at reduced intensity the replacement effort quickly solved the problem.
My primary use of the opto-isolated relays has been as a computer interface in industrical test systems. 100,000 hours of on time before a 3% reduction in illumination, and the associated increase in turn-on time would be no problem, since the production lifetime of the product tested may not be that long. And for those very long-life products another few milliseconds of response time would not be a problem either.
The other use of opto-relays is for on-off cycling of heaters in temperature controlled systems, where electrical heater powr is cycled to control temperature. For those applications with the zero-crossing switching the problem is even less likely to be noticed or to cause problems. It might possibly have some effect in motion control systems,but that is a different realm completely.
Transfers the control of a large number of motion axes from one numerical control kernel to another within a CNC system, using multiple NCKs, and enables implement control schemes for virtually any type of machine tool.
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