SIS signal isolation
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For signals from the field such as valve position and liquid level (intrinsically safe), can relays be used in place of safety barriers?
Shouldn’t the valve position and liquid level be 4-20mA? How to use a relay? If you’re referring to a Namur switch signal, it requires an 8V power supply. What do you plan to use for powering it?
There was a scene where I saw it done that way, and I couldn’t figure out the principle behind it. The on-site instrument technicians couldn’t explain it either
Haven’t seen it; looking forward to an expert explaining it
Is the liquid level a liquid level switch? The relay cannot be used to replace the NUMER signal from the level switch; however, the digital signal can be replaced by a safety barrier. The valve position is acceptable; any contact-type digital signal will do
I get it roughly; what you’re referring to are most likely switches – level switches, valve position switches. If they are dry contacts, a 24V supply connected in series to the circuit will work, but it’s not recommended. It’s still recommended to install a isolation fence.
Intrinsic safety is only considered such when it’s used in conjunction with a safety barrier. If there are no explosion-proof requirements, it can be modified freely :lol