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Explain about 4 wire instrument concept & tell about its
wiring fron sensor in Field to PLC panel.Explain with an
example?

Question Posted / ramaswamy and karuppusami

Answer Posted / ramaswamy and karuppusami

Usually in 2wire transmission, 24v supply is given and o/p
in mA are taken through single pair cable. e.g: Transmitters.

But in 4wire system, supply is provided in separate single
pair cable and o/p is taken through another cable. e.g :
local speed indicator device: i/p = 230v and o/p = 4-20
mA(Both are in separate cables ).

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