NPN Inductive Proximity Sensor

The operation of the NPN inductive proximity sensor is based on two key parts:

• Detection principle: The high-frequency oscillation circuit inside the sensor will generate an alternating magnetic field. When a metal object enters the magnetic field range (within the detection distance), eddy currents will be induced inside the metal, causing the amplitude of the oscillation circuit to decay. The sensor determines whether there is an object approaching by detecting this decay.

• Output characteristics: When a metal object is detected, the internal NPN transistor is turned on, the output end (OUT) is connected to the negative pole of the power supply (GND), and the output is low level (0V); when there is no object, the transistor is cut off and the output end is suspended (high level state, which needs to be achieved through a pull-up resistor).

1. Detection performance: Accurate identification of metal targets
Non-contact detection
Fast response speed
Strong anti-interference ability

2. Output characteristics: Adapt to the leakage control system
Low-level output logic
Open collector design

3. Structure and durability: Adapt to the industrial environment
Compact appearance
High protection level
Long service life

1) There is a difference between two-wire and three-wire proximity switches. Three-wire proximity switches are divided into NPN and PNP types, and their wiring is different.

2) The wiring of the two-wire proximity switch is relatively simple. The proximity switch can be connected in series with the load and then connected to the power supply.

3) The wiring of the three-wire PNP NPN inductive proximity sensor: the red (brown) wire is connected to the positive end of the power supply; Connect the blue wire to the 0V end of the power supply; The yellow (black) line is the signal and should be connected to the load. The other end of the load is connected as follows: for NPN-type proximity switches, it should be connected to the positive terminal of the power supply; For PNP-type proximity switches, they should be connected to the 0V terminal of the power supply.

4) The load of the proximity switch can be a signal light, relay coil, or digital input module of a programmable logic controller (PLC).

5) Special attention should be paid to the type selection of the three-wire proximity switch connected to the PLC digital input module. PLC digital input modules can generally be divided into two types: one type has a common input terminal of negative power supply, and the current flows out from the input module. At this time, NPN-type proximity switches must be used; Another type of common input terminal is the positive power supply, and current flows into the input module. At this time, a PNP-type proximity switch must be used. Don't choose the wrong one.

6) Working conditions limit the two-wire proximity switch. When it is turned on, the switch itself generates a certain voltage drop, and when it is turned off, there is a certain residual current flowing through it. Although the three-wire proximity switch has an additional wire, it is not affected by adverse factors such as residual current and works more reliably.

7) Some manufacturers will simultaneously output the "normally open" and "normally closed" signals of the proximity switch, or add other functions. In this case, please follow the product manual for wiring.

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