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I'm designing some boards for an industrial application. Basically, these are boards that verify the correct functioning of some power supplies (they measure the output voltage and check some POK signal and report the status via a message on the serial port).

My question is, do these boards have to have an isolated power supply and isolated analog inputs? If so, what could be the problems I might have if I don't do isolated inputs? Or what could be the benefits of making the inputs isolated?

To clarify, this is the situation: enter image description here The PSU powers the SYSTEM, while the board on the left has to monitor the power supply. I only drew some of the analog inputs, there are also other analog in for other voltages, but they are all in the same situations. The power supply of the board is also taken from one of the analog inputs, probably from the +48V one.

Federico Massimi
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  • More than likely but, without much more detail, this is impossible to to be sure about. – Andy aka Dec 14 '22 at 10:38
  • I don't think we have enough information to answer that. Especially about the isolated inputs. – Simon B Dec 14 '22 at 15:59
  • I would isolate the communication output. You could end up with some undesirable behaviour when you attach the communication ground to the common of the supply. Isolating the comms is easiest and cheapest and a well solved problem. – Bryan Dec 15 '22 at 01:30

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If it is monitoring a single power supply or several with their grounds tied together then shouldn’t need true isolation just maybe a high impedance input with over voltage protection. Then just isolate the serial port to be safe

ScottK
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  • Okay. There are actually two serial ports, one external RS232 (to connect a user's PC) and one internal RS422 to possibly connect other boards. Do they both have to be isolated? – Federico Massimi Dec 15 '22 at 09:34
  • I would isolate both if the other boards have some other power source. If the power is shared between boards then probably not necessary to isolate. – ScottK Dec 15 '22 at 12:30