Answer / carl_ellis

Often identification data is printed on proximity (or prox) sensor's label but it is not uncommon for the label to damaged, missing or unreadable.

Many prox sensors are DC powered, 3 wire devices that conform to a standard wiring color code:

brown is (+) supply voltage, typically 24Vdc
blue is (-) supply voltage common or return
black is the sensor's switched output

To test a 3 wire sensor to determine whether it is a PNP or NPN type you need a DC power supply and a DC voltmeter.

Set the meter to DC voltage to a range greater than the supply voltage (typically 24Vdc), like 50/100/200/600V

The black meter probe should be in the 'common' meter socket
The red meter probe should be in the DC 'volts' socket

Connect the sensor's brown wire to the power supply (+)
Connect the sensor's blue wire to the power supply (-).

Turn the power supply on.

Ensure that the prox sensor is not triggered by presence to an object.

Connect the black meter probe to the blue sensor wire.
Connect the red meter probe to the black switched signal output sensor wire.

If the meter is connected to a PNP device, the meter will read 0V.
If the meter is connected to an NPN device, the meter will read 24Vdc.

Force the sensor to change state/output by detecting an object.
- If it is an inductive proximity switch, place a piece of metal in front of the sensor.
- If it is a photoelectric sensor, block the photoelectric beam.
- For an ultrasonic sensor or a capacitive sensor, you can just use your hand to make the sensor output. Some prox sensors use an LED that lights up when the sensor detects an object.

With an object present, a PNP device's output will change and the voltmeter readout will read 10V to 30V. This is also known as a "sourcing" device.

With an object present, an NPN device's output will change and the voltmeter readout will be 0V. This is also known as "sinking."

Another test to check for PNP:
Connect the power supply (+) to brown, (-) to blue.
Connect the red meter probe to the brown (+) sensor wire.
Connect the black meter probe to the sensor's black signal output wire.

When sensing no object, the signal output will be 10V to 30V.

When sensing an object, the signal output will be 0V.

Another test to check for NPN:
Connect the power supply (+) to brown, (-) to blue.
Connect the red meter probe to the brown (+) sensor wire.
Connect the black meter probe to the sensor's black signal output wire.

When sensing no object, the signal output will be 0V.

When sensing an object, the signal output will be 10V to 30V.

What is offset in a control system.

2 Answers   Sabic,

---

which one is best profibus or RS485 for communication?

2 Answers   Honeywell,

---

What are the type of bonnets in the control valves?

0 Answers   CCIE,

---

Q- What are the application in which PNP transistor is preferred over NPN ?

0 Answers  

---

How to decrease opening & closing time of on/off valve?

0 Answers   UPL,

---

---

What does threshold mean? what does tolerance mean?

1 Answers   DEWA,

---

Foe selecting control valve if i have the min,normal & max data of flow rate,inlet pressure& outlet pressure,inlet tem.&density than how can i assure that these data are correct,pl. let me know if therew there is any method to check it.& also how we assure that the Cv we get from this data is suitable for valve for controlling require flow.

3 Answers   HPCL,

---

what is unit and element of viberation?

1 Answers   Kentz, KOC,

---

what are the values of fuel flow rate in various places in boiler.

0 Answers  

---

what is Potential free contact? where it is used?

3 Answers   Engineers India Limited,

---

how to design orifice plate?what is the equation?

0 Answers   REL,

---

what is the advantage by using PID controller than P& PID?

1 Answers  

---