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Sheet N° 68

How to check a 2, 3 & 4 wire sensor

Electrical training

inductive or capacitive sensor
 

1-Role.

The sensors make it possible, for example, to check the position or the presence of a piece.

The inductive sensor detects ferrous objects while the capacitive sensor detects any material.

These detectors are active sensors. That is, they must be powered to working. These sensors must be tested with the power on.

The sensors can have 2, 3 or 4 wires. They are PNP or NPN type transistorized.

2- 2- wire sensor.

2-wire sensor
 

This type of sensor can be with NO or NC contact (Fig. A).

NO: Normally open

NC: Normally close

This type of sensor is not polarized and works in alternating or direct current.

 

2-wire sensor check
 
 

Test (Fig. B): The test is carried out with the sensor connected and powered on.

     - Check the integrity of the sensor.

     - Check the condition of the connections.

     - Install a voltmeter in parallel withrelay K1, insert a piece to be detected and check the voltage change.

To note: Often, sensors have a light diode that activates when they detect. Be careful that this diode does not validate the sensor check. The diode may be defect and the sensor may be working fine or the diode may be working and the sensor may be fault.

 

3- 3- wire sensor.

 

3-wire sensor
 

This type of sensor can be with NO (Normally Open) or NC (Normally Closed) contact.

This type of sensor operates on direct current. It is PNP or NPN type transistor.

We find:

     - A power supply, terminal 1 (brown wire) is connected to the positive terminal and terminal 3 (blue wire) is connected to the negative terminal.

     - A signal output at terminal 4 (black wire): A positive output signal for a PNP type sensor or a negative output signal for a NPN type sensor.

 The sensor can be wired connected to a terminal block or connected with a 3 or 4 pin connector.

 
 
3-wire sensor check

Test (Fig. D): The test is carried out with the sensor connected and powered on.

     - Check the integrity of the sensor.

     - Check the condition of the connections.

     - Install a voltmeter between the brown and blue wire to check the power to the sensor.

     - Install a voltmeter between the black and brown wire for a NPN sensor or between the black and blue wire for a PNP sensor. Place a piece to be detected and check the voltage change.

Test box sensor

When the sensor is connected with a connector, an interface box must be used for the checking.

test box 3 - wire sensor

     - (1,2,3): Disconnect the sensor and insert the box in the correct direction (male-female or female-male). This box has 4-pin M12 connectors.

     - (4): With a voltmeter, check the power supply to the sensor on terminals 1 & 3.

     - (5,6): Put a piece to be detected and check the voltage change on terminal 4 & 1 for a NPN sensor or between terminal 4 & 3 for a PNP sensor.

To note: Often, sensors have a light diode that activates when they detect. Be careful that this diode does not validate the sensor check. The diode may be defect and the sensor may be working fine or the diode may be working and the sensor may be fault.

4- 4- wire sensor.

 
4-wire sensor

This type of sensor has 2 contacts. NO (Normally Open) and / or NC (Normally Closed).

This type of sensor operates on direct current. They are PNP or NPN type transistorized.

     - A power supply, terminal 1 (brown wire) is connected to the positive terminal and terminal 3 (blue wire) is connected to the negative terminal.

      - A first signal output at terminal 2 (white wire): A positive output signal for a PNP type sensor or a negative output signal for a NPN type sensor.

     - A second signal output at terminal 4 (black wire): A positive output signal for a PNP type sensor or a negative output signal for a NPN type sensor.

The sensor can be wired connected to a terminal block or connected with a 4 pins connector

 
4-wire sensor check

Test (Fig. G) : The test is carried out with the sensor connected and powered on.

     - Check the integrity of the sensor.

     - Check the condition of the connections.

     - Install a voltmeter between the brown and blue wire to check the power to the sensor.

     - Install a voltmeter between the brown and blue wire to check the power to the sensor.

      - Install a voltmeter between the black and brown wire for a NPN sensor or between the black and blue wire for an PNP sensor. Put a piece to be detected and check the voltage change.

      - Install a voltmeter between the white and brown wire for a NPN sensor or between the white and blue wire for an PNP sensor. Put a piece to be detected and check the voltage change.

 
Test box sensor

When the sensor is connected with a connector, an interface box must be used for the checking.

 
test box 4-wire sensor
 

     - (1.2.3): Disconnect the sensor and insert the box in the correct direction (male-female or female-male). This box has 4-pin M12 connectors.

     - (4) With a voltmeter, check the power supply to the sensor on terminals 1 & 3.

     - (5,6): Put a piece to be detected and check the voltage change on terminal 4 & 1 for a NPN sensor or between terminal 4 & 3 for a PNP sensor.

     -(7,8):  Put a piece to be detected and check the voltage change terminal 2 & 1 for a NPN sensor or between terminal 2 & 3 for a PNP sensor.

 

To note: Often, sensors have a light diode that activates when they detect. Be careful that this diode does not validate the sensor check. The diode may be defect and the sensor may be working fine or the diode may be working and the sensor may be fault.

 

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