Can I connect Inductive Proximity sensor to two different PLC
If the two systems share a common negative then yes, if the PLC has an NPN (sourcing) input but it could cause problems.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Opto-isolated feed to PLC.

With the addition of a resistor and opto-isolator you can ensure trouble-free operation due to the complete isolation between the two systems.


Calculate R1 to give about 10 mA through D2. D2, being an infrared LED will drop about 1.4 V at this current.
Q2 can be connected to the PLC input and common but observe correct polarity. One of the beauties of this arrangement is that Q2 can drive a PNP (sinking) or NPN (sourcing) input.