Proximity Sensor Types

In this guide, we will see what is a proximity sensor, the types of proximity sensor and their uses, and finally, we will do a comparison between them.

What is a Proximity Sensor?

The proximity sensor is a device used to detect nearby objects. When the object comes into its sensing area an electrical signal gets generated and this helps to detect the object.

Types of Proximity Sensor and their Uses

1. Capacitive Proximity Sensor

Capacitive proximity sensor

It works on the principle of varying capacitance. So, as the capacitance changes corresponding output signal generated also changes. This capacitance change is marked by the shape of the object and the distance of the object from the sensor.

Capacitive proximity sensor construction

The sensor consists of an oscillator, trigger circuit, and output switching device. As the target enters the electric field generated by the sensor, the electric field generated gets obstructed by the target resulting in a change in capacitance which results in a change in amplitude of the oscillator circuit. When the target moves further from the sensor the amplitude of oscillation decreases and when the target comes close amplitude increases. This change triggers the trigger circuit resulting in a change in the output of the sensor and thus glowing the output sensor led.

Application

As shown in the above image they can be used to detect objects on the conveyor belt.

2. Inductive Proximity Sensor

Inductive Proximity Sensor works on two principles

 

Faraday's Law of induction


When an electrical conductor is placed in a magnetic field, eddy currents are produced in the conductor.

 

Lenz’s Law

Lenz’s LawThese eddy currents generate a magnetic field that opposes the cause or the magnetic field which generated it.
This type of sensor has a wire wound around typically an iron core. As shown in the above figure, an alternating current is applied to the coil which generates a magnetic field around it. This magnetic field gives rise to an eddy current in the electrical conductor. These eddy currents then generate an eddy current magnetic field that opposes the electromagnetic field from the sensor. When the target is taken close to the sensor the electromagnetic field from the sensor gets reduced, which decreases the amplitude of the electromagnetic field. When it decreases beyond the threshold trigger circuit activates the output. This helps to identify that object has come into the desired vicinity of the sensor.
Note: It has a similar internal circuit as that of the capacitor sensor.

Inductive proximity sensor

Refer to this guide for interfacing proximity sensor with Arduino to get a hands-on experience with this sensor.

3. Magnetic Proximity Sensor

Magnetic Proximity sensor

This sensor works on the principle of the Hall effect. As shown in the figure, a potential voltage is applied across a hall element such as a hall element made of tin. So positive and negative charges start flowing. Now, when a magnet is brought in the vicinity of the hall element material, negative and positive charges get

accumulated across the opposite ends of the plate. When we measure the voltage across it a tiny voltage in microvolts is obtained. This is usually amplified by an amplifier. When the object is taken closer a higher potential gets generated across the plates and when it exceeds the threshold output is set to high. There are various other technologies too used in magnetic proximity sensors such as variable reluctance, reed switches, GMR (Giant Magneto-Resistive effect) inductive

4. Optical Proximity Sensor

Optical Proximity sensor

Optical proximity sensor consists of a transmitter and a receiver. The transmitter circuit consists of a photo transmitter that sends light out by converting electrical energy into light. This light gets bounced back from the target which is received by the photo receiver. There are three types of optical proximity sensors: through-beam sensor, retro-reflective sensor, and diffuser sensor.

5. Ultrasonic Proximity Sensor

Ultrasonic Proximity Sensor

An ultrasonic proximity sensor consists of a transmitter and receiver. As shown transmitter sends out a sound wave and the receiver detects the reflected wave from the object. You can refer to this guide Arduino Interfacing with an ultrasonic sensor if you want to try something hands-on.

Comparison Table of Proximity Sensors

 Parameter

Capacitive Proximity Sensor

Inductive Proximity Sensor

Magnetic Proximity Sensor

Optical Proximity Sensor

Ultrasonic Proximity Sensor
Sensing distance (mm) 1-35mm (some sensors up to 70mm) Up to 60 mm Up to 80 mm 2-30mm Up to 1000mm

Vibration tolerant

Excellent Excellent Excellent Excellent Poor
Sensitivity Very sensitive to changes in environmental conditions such as temperature and humidity. Adaptable to harsh environments Susceptible to magnetic interference Sensitive to dust and lubricants Temperature variations( since the speed of sound is dependent on temperature
Sensing object material The object can be made up of any material Ferrous metals such as iron and steel.
Non-ferrous metals sensing range decreases(will be given in datasheet)
The object should be of Magnetic material only. The object can be made up of any material. ( fails for a transparent object ) The object can be made up of any material. ( works for transparent objects)
Cost Medium Low Low Medium High
Size small small small small small
Application They are used for detecting parts in conveyors, workstations, and robots. Foil seal detection inside plastic caps, to count metal cans. Used to detect the open or closed status of windows, gates, and doors.
Used in the food industry.
Automatic soap dispenser, optical heart rate monitor, optical liquid level indicator. Liquid level control, robotic sensing, counting people, automobile self-parking technology, and anti-collision safety systems.

Components and Supplies

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