Video summary

What is PNP Sensor? Working, Wiring and Testing

Main summary

Key takeaways

Technology

Summary of the Video (PNP Sensor: Working, Wiring, and Testing)

The video explains how PNP (sourcing) proximity sensors work in industrial automation using 24V DC discrete I/O. It also covers wiring a PNP sensor to a PLC, common setup considerations, and how to test/verify the sensor with a multimeter.

Key Technological Concepts / Definitions

  • Industrial automation systems rely on discrete input/output signals from sensors.
  • Many industrial sensors use 24V DC, where PNP vs. NPN naming is frequently confusing.
  • PNP stands for “positive–negative–positive” (mnemonic: the middle N reminds you that the load should connect to the negative side of the supply).

Working Principle of a PNP (Sourcing) Sensor

  • The video shows an example circuit using a two-wire proximity sensor + load (light bulb):

    • When no target is detected, the sensor does not conduct.
    • When an object (metal target) is detected, the sensor activates so current flows from:

    + supply (brown wire) → sensor → load (through blue wire) → − supply

  • Because of this behavior, a PNP sensor is called a sourcing sensor (it provides current/power to the load side).

Internal Design of a 3-Wire PNP Sensor (What’s Inside)

A typical 3-wire PNP proximity sensor includes:

  • Sensing element: detects nearby objects in range.
  • PNP transistor: acts like a switch controlling current flow.
  • The sensor output is controlled by turning the transistor on when a target is present and off when absent.

Wiring a 3-Wire PNP Sensor (Color-Coded)

  • Brown wire: power (+24V)
  • Blue wire: power (0V / negative terminal)
  • Black wire: signal output to the input/load/PLC input

The PNP transistor is positioned for positive switching, and the sensor’s negative side must connect to the load/common terminal to complete the circuit.

Connecting a PNP Sensor to a PLC (Sourcing vs. Sinking Compatibility)

The video highlights two key compatibility points:

  1. PLC discrete inputs can be configured as sourcing or sinking (the focus is on matching the PLC input type).
  2. The selected field sensor type (PNP/NPN) must match the PLC input module type.

For the discussed case:

  • Sensor output (black wire) → PLC input
  • PLC common terminal tied to the − side of the power supply

When the sensor detects a target:

  • The sensor transistor turns on (acts like a closed switch),
  • Current flows:

+24V → sensor → PLC input → PLC common → −24V

Testing / Identifying a PNP Sensor Using a Multimeter

Testing assumes a 24V DC supply.

  • If no object is detected:
    • The sensor output voltage should be low / near 0V at the sensor output (input to PLC).
  • If a metal object is detected:
    • The output voltage should rise to nearly the supply voltage.
    • Expected reading is typically about 1–2V lower than the supply voltage due to transistor behavior.

Multimeter connections described:

  • Red lead → black (sensor output) wire
  • Black lead → ground / negative

Main Speakers / Sources

  • Primary source: The video narrator/presenter (no specific name given in the subtitles).

Original video