NPN Sensor Explained | Working, Wiring, and Testing

🎥 When dealing with 24-Volt DC sensors, it is common to encounter the term NPN, which can be challenging to understand as it is frequently used in the industry.

By watching this video, you’ll get the answer to these questions:
- What is an NPN sensor?
- How to test an NPN sensor?
- How to wire an NPN sensor?
- What is an NPN output sensor?
- How does an NPN sensor work?
- What is an NPN sensor used for?
- How to connect an NPN sensor to a PLC?
- What are the components of an NPN sensor?
- What are some typical applications of NPN sensors?

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💬 Video Summary:

NPN Circuit
- The first step is to check if the circuit is designed to accommodate NPN sensors

- The NPN is shorthand for negative-positive-negative. The middle letter P in NPN stands for Positive polarity and serves as a reminder of a direct connection of the load to the Positive side of the power supply.

NPN Sensor Diagram
- The internal circuitry of a 3-wire NPN sensor typically contains two main components: the sensing element circuit and an NPN transistor.

NPN Sensor Wiring
- Active solid-state 3-Wire NPN sensors typically require an operating power to function.

- The power wire, identified by its brown color, is connected to the positive side of the power supply, while the blue wire is attached to the power supply's negative terminal.

- The signal output wire of the sensor, which connects to the input terminal of the load, is identified by its black color. This wire is the third wire of the sensor.

NPN Sensor Working
- When the 3-wire NPN sensor doesn't sense any metal object, the active line goes low, causing the NPN transistor to switch off and function somewhat as an open switch. So, it leaves the NPN output circuit open, resulting in no current flowing through it and the alarm device remaining off.

- The sensor's detection of a metal object causes the active line to go high, then turns on the NPN transistor to act like a closed switch and activate the alarm device.

- Since the NPN sensor can be considered as receiving input power from the load for sinking it to the ground, it is commonly referred to as a sinking sensor.

NPN Sensor Connection to PLC
- It is crucial to select a field sensor type that is complementary or opposite to the type of PLC discrete input module used to have reliable performance. Since the NPN or sinking sensor has been incorporated into this circuit, it is imperative to use a sourcing PLC discrete input module to match it.

- Finalizing the circuit requires attaching the sensor output, represented by the black wire, to the input of the PLC module and then linking the common terminal of the PLC module to the power supply's positive terminal.

Checking NPN Sensor
- Lastly, you will discover how to test the NPN sensor to ensure it operates correctly. To do so, make sure you have a multimeter on hand.

- Attach the multimeter's red lead to the NPN sensor's black wire and connect the black lead of the multimeter to the ground.

- If the NPN sensor doesn't detect a metal object, then you can expect that the sensor's output voltage will be high, which indicates that it is supplying a voltage nearly equivalent to the power supply to the input of the PLC module.

- And you expect when a metal object enters the detection range of the sensor, the sensor's output voltage will be pulled down to almost zero volts.

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⏰ TABLE OF CONTENTS ⏰
00:00 24-Volt DC Sensors
01:13 NPN Circuit
02:36 NPN Sensor Internal Diagram
03:22 NPN Sensor Connection
04:24 NPN Sensor Working Principle
05:32 NPN Sensor Wiring to PLC
07:30 NPN Sensor Testing

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