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A Comprehensive Guide to Proximity Sensor Technology

An example of proximity sensor
An example of proximity sensor

In today’s world, the proximity sensor is one of the most widely used pieces of technology. Its applications are vast and include everything from industrial automation to object detecting in security installations. Here, you’ll learn all about proximity sensor technology and understand its many uses.

What Is a Proximity Sensor?

A proximity sensor is a type of sensing device that, using various means, detects the presence (or absence) of objects without physical contact. In other words, it senses when the object is within its vicinity or area of detection and trigger an output signal. Here’s is what you need to know about these sensors.

  • A typical proximity sensor device is composed of these parts: the sensing head or face, sensor body, and sensor connections.
  • The sensing head sends the signal to detect the object and receives a reply when contact is made.
  • The sensor body houses the electronics, which interpret the signal and send it back through the connections.
  • The proximity sensor connection links it to a power source and/or an output device.

Proximity sensors are also known as non-contact sensors and used in many different industries and applications, such as automated manufacturing processes and industrial robotics. Proximity sensor technology is also used in consumer electronic devices like phones and computers.

After the proximity sensor definition and features, let’s explore the circuit that makes up its operation. This will help you understand how the sensor works as well as the purpose that it serves, as we will be seeing shortly after.

A typical proximity sensor wiring diagram
A typical proximity sensor wiring diagram

Proximity Sensor Circuit

The typical proximity sensor circuit comprises two major sections: a sensing circuit to detect objects, and a driver circuit to control the output. The sensor circuit is usually composed of an oscillator or mutual induction device, which produces a signal when it detects an object in close proximity.

The signal is then sent to the driver circuit. This is the part of the sensor that takes the input signal and amplifies it to the appropriate level before sending it to output devices such as relays or a PLC. The output can then be used to control other systems, such as motors or lights

Depending on the type of proximity sensor circuit, the output may be adjustable in order to detect objects at different distances. This alters the sensitivity level of the device. With this information, let’s now see how a proximity sensor works.

Proximity sensor connections
Proximity sensor connections

Proximity Sensor Working Principle

So, how does a proximity sensor work? The basic principle is that when an object comes within close proximity to the sensor, it changes something (such as frequency or intensity) that the sensor can detect. This differs from other sensing technologies such limit switches, which require direct contact with the object being detected.

Depending on the type of sensor, the sensing mechanism may be an oscillator that generates electromagnetic waves, a sound waves generator, or a light emitter-receiver unit. It can also be a capacitive sensor that uses an electric field to detect objects. Here’s the general working of proximity sensor explained.

  • When the object comes in close proximity to the sensor, it changes either the frequency or intensity of the waves that are generated by the sensor.
  • This alteration is detected and an output signal is sent from the driver circuit to activate a switch or relay.
  • The switch or relay will then trigger different types of actions depending on its applications.
  • You can install proximity sensors to detect objects of different shapes and sizes, based on the range that the sensor is able to detect.

A proximity sensor module is also either a PNP or NPN type. PNP type sensors emit a positive output signal when an object is detected, while NPN type sensors emit a negative output signal as described below.

Proximity Sensor PNP

A PNP proximity sensor can be identified as a switched positive or active-high-output sensor. That means its load is always connected to ground or negative, and only connects to the positive when an object is detected. In other words, the output signal switches to low when no object is detected and high when it senses no target.

Proximity Sensor NPN

An NPN proximity sensor is identified as a switched negative proximity sensor, or active low — the opposite of the PNP type. Unlike a PNP type, it emits an active low output signal, or a signal that is constantly in the low state until an object is detected. The output signal will, therefore, switch to high when a target is detected.

Proximity sensor range
Proximity sensor range

Proximity Sensor Range

The proximity sensor range is used to refer to the maximum distance at which the sensor can detect an object. This is commonly measured in millimeters and depends on the type of sensor used, as well as the intended application.

For example, the inductive proximity sensors commonly used in industrial applications need to detect objects at a different distance than those used in consumer product applications.

So while an inductive industrial proximity sensor may have a range of up to 80 mm, a capacitive proximity sensor for mobile phone use would typically have a much smaller detection range of only a few millimeters.

The different detection distances for proximity sensor mostly lie between 1 and 100 mm. That said, some, such as the ultrasonic proximity sensor, can find targets that are several meters away.


An example of proximity sensor function in industrial applications
An example of proximity sensor function in industrial applications

Proximity Sensor function

The main function of proximity sensor devices is to detect the presence of an object without actually making contact with it. This makes it perfect for applications where physical contact between objects may not be desirable or feasible.

Proximity Sensor Uses

The many different proximity sensor uses includes industrial automation, robotics, security systems, medical equipment and automotive industry. For example, these sensors are commonly installed in robots to detect objects in their path and to avoid collisions.

In safety and security applications, proximity sensors can be used to trigger alarms when human or other target is detected. Other proximity sensor uses include human-machine interactions, such as activating an alarm when hands are placed near a machine or device, or to detect and respond to motion in a room.

In the car industry, the automotive proximity sensor is commonly are used for detecting other vehicles in order to provide advanced warning systems and ultimately improving safety. In medical applications proximity sensor uses include monitoring equipment components and counting systems.

Proximity Sensor Advantages and Disadvantages

Proximity sensor applications have their upsides and downsides, which users must know about. The advantages and disadvantages proximity sensors, based on the above uses, include the following.


  • Proximity sensors can detect objects without any physical contact, making them suitable for delicate or hazardous environments.
  • They are reliable and require minimal maintenance, which makes them an ideal choice for most industrial automation and other applications.
  • The proximity sensor cost is generally very low, from price to installation and power consumption.
  • Proximity sensors offer long service life owing to contactless operation.
  • Thee sensors offer superb operational stability to provide greater accuracy and other benefits.


  • Some proximity sensors may have a limited operating range, and can only detect objects within a certain distance.
  • Some sensors may not be suitable for objects that move quickly, as their response time is low.
Proximity sensor vs. limit switch
Proximity sensor vs. limit switch

Proximity Sensor vs. Limit Switch

Both proximity and limit switches are primarily used to detect the absence or presence of objects. However, they use different technologies and, therefore fit different applications. So, how is proximity switch differentiated from limit switch?

Limit switches are electromechanical, requiring physical contact with an object to detect it. Proximity sensors do not require physical contact and can detect things from a certain distance away.

Because proximity sensors do not need to be in contact with an object, you can use them in many situations where limit switches may not be suitable, such as debris-prone environments.

Additionally, proximity sensors are not subjected to wear by the target since they do not need to physically contact it.

Limit switches tend to be generally larger than proximity sensors. In comparison, proximity sensor dimensions vary widely, with the device size ranging from small to very large.

An example of proximity sensor (1)
An example of proximity sensor

Price of Proximity Sensor

For anyone intending to buy proximity sensor products, the price is one of the things that influence choice. While there is no one-size-fits-all sensor, understanding the different types of these sensors and their prices will help you select the most suitable option for your application needs.

The price of proximity sensor can vary widely, depending on its quality and specifications. Usually, the higher the features of a particular model, the more expensive it will be. That said, different types of proximity sensors may also come at different prices.

For example, the ir proximity sensor price may range from less than a dollar to over $50 while an ultrasonic sensor goes for as high as $400. Overall, when choosing a proximity sensor, we recommend that you consider the application that you need it for besides price.


Proximity sensors are a type of sensor technology that can be used for a variety of applications, ranging from industrial automation to robotics and security systems. They can detect objects at different distances to provide either an active high or low output signal. We hope this article has helped you understand the proximity sensor technology and its applications.

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I am William, Electrical Engineering Author. Dedicated to writing technical articles on Timer Relay, Monitoring Relay, Surge Protection Device and other electrical devices. With 7 years of writing experience, I am committed to providing accurate and in-depth expertise to my readers.

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