PLC – How to Connect Multiple Sensors to Single PLC Input

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Hello. I have a scenario where I have multiple PNP "error signal" from several sensors (let's assume 3 for now). If the sensor output is HIGH, then there is error. If the sensor output is LOW, then there is no error. The design is that if any of the sensor detect error then the PLC input will be HIGH. My question is, suppose if all three sensors detect error, it means all three will send voltage to the same port in PLC. Will it cause over current and damage the PLC input? Is the current in PLC port = current sensor 1 + current sensor 2 + current sensor 3?

Best Answer


simulate this circuit – Schematic created using CircuitLab

Yo do only have to add three diodes D1-D3 to your PLC input. The currents don't sum, right the opposite. If only one sensor is HIGH, then the current through sensor and PLC input is the same, if more than one sensor is HIGH, then current through PLC input is the same, but current through sensors are divided.

You may also omit the diodes and connect them parallel if they are industrial sensors. I do connect, for example photocells, parallel to increase the detection zone.