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Proximity or presence sensor, what it is and what it is used for

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In recent years, proximity and motion sensors have taken part in our language, precisely because of the technologies developed. We have often heard of these objects in presentations of new smartphones. But what are they and what are they for?

Here is an overview of proximity sensors and what types are on the market.

What is a proximity sensor?

The proximity sensor is a device that allows you to detect the presence of a body or an object in the immediate vicinity. But in what way? This device exploits the property of the electromagnetic waves that it can emit: the return of the waves makes it possible for the device to detect objects on its way or not.

Usually, these sensors are inserted on a phone and take advantage of infra-red rays, but the typical functioning is that of elements such as the parking sensors present on the car. The proximity or presence sensor is used in many cases and, therefore, is used to detect an object.

There are many different models, which use technology to detect an object or body in the immediate vicinity. There are two terms that are often used: one is the switching speed, which is the speed at which the signal is processed, and the other is the nominal distance, which is how far the sensor reaches in optimal conditions.

What is a proximity sensor for?

The question is obviously spontaneous: what is such a device for? This type of device, as we have seen, is used in various situations. If installed in a car, it can be very useful when parking or in traffic. If active, they allow us to understand if there is a body near the car (for example a cyclist or a motorcyclist) and we can certainly pay more attention.

Often, these devices are also installed on a smartphone. Considering that the touch screens are started with the simple touch, in this case the motion sensor will activate the touch only by a finger-touch but not, for example, when we talk on the phone.

How a proximity sensor works

But what is the real operation of this device? The proximity or motion sensor is a device that can emit and receive waves. When the waves are emitted they have a return as soon as they encounter an obstacle in front of them.

Being predisposed to return, on the basis of the intensity, you will have the possibility to understand at what distance the object is, and the sensor will activate or not accordingly. The proximity sensor could be compared, in a distant way, to the echo-sounder of ships: the measurement takes place precisely on the basis of the return of the wave echo.

The operation is practically identical: based on the return, the sensor will measure the distance to the nearest object and activate the functions for which it was programmed.

Different types for different uses

Obviously there are many models of each proximity or motion sensor, since each type allows a different application. In fact, the development of this technology has gone through several stages and has allowed us to come up with really useful models, used in every field. Just think of a smartphone that turns off the touch when in proximity to the ear or the car’s parking sensor. A set of problems solved with a single device.

Optical proximity sensors

Optical proximity sensors have the same basic operation as proximity sensors but use a light beam to detect the object. Usually the beam is infra-red: this technology is used to prevent interference with the surrounding light.

The nominal sensitivity, that is the maximum that the beam can reach in optimal conditions, is 50 meters. Usually this technology is applied on the latest generation smartphones.

Inductive proximity sensors

This type of sensor exploits reluctance, that is the reflection phenomenon that occurs when an object is crossed by electromagnetic waves. They have a certainly less widespread field of application, given that in order to have feedback there must be a material that has ferromagnetic properties.

The nominal capacity, compared to other materials, is very low: we are talking about a few millimeters. The proximity or presence sensor is certainly much more sensitive but has a minor application.

Magnetic proximity sensors

This proximity sensor also exploits the magnetic properties, developing the Hall Effect, which creates a potential difference between an electric and a magnetic field. Compared to other sensors, the nominal range varies according to the magnetic field created.

They have excellent sensitivity and excellent signal switching speed, i.e. wave response. Their operation is still due to a magnet, therefore disturbances in the presence of other sources can be a real problem.

Capacitive proximity sensors

Another type of proximity sensor is the capacitive one, which is based on the electrical capacity that can be developed by a capacitor. The switching of the signal, that is its interpretation and reception, is therefore due to the generated field.

They have a higher rated range than inductive ones and are not disturbed by electromagnetic signals. These sensors are also applied in precision mechanics and have a less commercial range than infra-red ones.

Ultrasonic proximity sensors

One of the best known technologies is certainly that of ultrasonic sensors. The principle is that of sonar, that is an emission of waves that allows the detection of objects based on the return.

The functions of these objects are highly customizable and allow you to have an incredible product, capable of having a truly incredible nominal range: we are talking about 10 meters and they can detect any type of object, made up of any material.

Use and applications also in machine vision

As we have seen, the proximity sensor or motion sensor has an application in many fields. This also depends on the type of technology in which it is used and what kind of waves it can emit.

Based on the object we have to detect, we will have the opportunity to understand which one is right for us or which one we are using. Sensors are also used and applied in machine vision because, having to reconstruct images in three dimensions on a surface in two dimensions, the use of sensors is very useful in order to have a precise detection of objects and also for dimensional control.

The high technology allows to develop many techniques and every device that allows machine vision has a motion sensor. The technology that uses the sensor allows a greater and more precise detection than other objects, thus arriving at an image that is ever closer to reality.

Considering that there are different types of proximity sensors and each one for a different application and field of use, we remind you that among the choice factors we must consider, above all, the switching accuracy and the nominal range.