Common - PLC input signal

Industrial control often use the input components are mainly switch, knob switch, button switch, trip switch, proximity switch, encoder, etc. , as shown in the figure below:

commonly used PLC input switch

these switches have two wire system ( Button, knob, travel switch) , three wire system ( Proximity switch) And four wire ( The encoder) , the switch input type NPN and PNP. NPN sensor output signal through the switch of the switch tube with low level ( Power source to 0 v) Connection, when the sensor received signal action, switch tube conduction, output low level signal; PNP output signal with high level ( Power supply 24 v) Connection, when the sensor received signal action, switch tube conduction, a signal output level.

line PLC input types: PLC wiring has a leak, the source input, PLC controller type input leakage, the diagram below:

so-called type input leakage type, source, the input is for PLC public end S/S, when the 24 v dc power flow from the public S/S terminals from the input terminal ( X) Leakage flow, becomes input, when the 24 v dc power from the input terminals ( x) Child into the outflow from the public, is the input source type, can be seen that when the input leakage public end S/S + 24 v dc power supply, input source type dc power 0 v S/S.

how to choose the switch type source input of the input type?

with a PLC basic unit can only use a connection leak or source, for two wire switch, two kinds of connection can be, the diagram below:

type leakage input

input source type

for three-wire system sensor wiring must pay attention to the connection, according to the instructions in the face of NPN in PNP sensor, NPN base open collector type leakage sensor is the corresponding PLC type input.

NPN sensor for PNP open collector type sensor need to select the PLC input source type.

such as listed above, the proximity switch and sensor are NPN, connection is as follows:

NPN proximity switch connected to the PLC

NPN coder and PLC connection

above is common input device is connected to the PLC control in the schematic, choose the corresponding PLC input type depending on the type of switch to be successful connection, be sure to check the main switch in connection type.

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