How to determine what kind of proximity switch used in the PLC -

proximity switch is very widely used equipment, industrial control automation industry access PLC can achieve the function of mechanical arm, location in detection. Its output form has two kinds of NPN and PNP. The two forms of proximity switch and PLC controller wiring is not the same, the output signal is different also. So, through the connection mode and the output signal to determine what kind of proximity switch used in the PLC.

1, the output form by nameplate query proximity switch

this is the most direct way of query through the nameplate products can query to the product technical parameters. If plaque fall off, can be judged through the connection mode and the output signal. Described below.

2, judging by an external resistor

close to switch is the core components of transistor, the output signal for the open collector output transistor OC, so it needs to be connected to the PLC through the external resistors.

NPN when use, you need to output end up by resistance to the power end; PNP when use, you need to output through a pulldown resistor to GND. So, you can check the other end of the external resistance to determine the output form of proximity switch.

if the resistance is power supply side, on the other side of the proximity switch as NPN; If on the other side of the resistance to the GND terminal, the proximity switch for the PNP. Pictured above is NPN proximity switch wiring diagram, this is the wiring diagram of the PNP proximity switch.

3, judging by the output signal

NPN proximity switch, when not reach the designated position signal, the output high level; Have in place signal output low level. PNP proximity switch, when not reach the designated position signal, the output low level; When in position signal output high level. So, according to the above information, induction of the proximity switch through the analog signal to judge.

the most quickly determine proximity switch is at the input to PLC NPN and PNP:

PLC input COM if pick up was the proximity switch power negative 0 v must be NPN

PLC input COM if pick up was the proximity switch the positive 24 v power supply must be PNP.

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