Answer Posted / chandrasekarapandian

4-20 mA is the universal standard.
Justification:
1. easily splittable ranges 0 % = 4mA
25 % = 8mA
50 % = 12mA
75 % = 16mA
100 % = 20mA
2. 4 to 20 mA passed over 250 ohms coil resistance will
produce a suitable voltage sourcew of 1 to 5 volt.
3. LIVE ZERO
If our sensor to PLC wire connecton is open PLC reads 0mA
where as if the input of sensor in ZERo PLC reads 4mA.

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