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10 May 2023

PROXIMITY OR PRESENCE SENSOR, WHAT IT IS AND WHAT IT IS USED FOR

Negli ultimi anni i sensori di prossimità e presenza hanno preso parte del nostro linguaggio, proprio per via delle tecnologie sviluppate. Spesso abbiamo sentito nominare questi oggetti nelle presentazioni dei nuovi smartphone. Ma che cosa sono e a cosa servono?

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

What is a proximity sensor?

A proximity sensor is a device for detecting the presence of a body or object in the immediate vicinity. But how? This device uses the electromagnetic waves' property it can emit: the return of the waves means that the device can detect or not detect objects in its path.

Usually, these sensors are inserted on a phone and make use of infrared rays, but this is the typical operation of elements such as parking sensors in cars. The proximity or presence sensor is used in many cases to detect an object.

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

Sensore prossimità | Vision Device

What a proximity sensor is used for

The question naturally arises: what is such a device used for? This type of device, as we have seen, is used in various situations. If installed on a car, it can be very useful when parking or in traffic. If activated, they allow us to see if there is a body in the vicinity of the car (e.g. a cyclist or motorcyclist) and we can certainly be more careful.

Often these devices are also installed on a smartphone. Considering that touch screens are initiated by a simple swipe, in this case the motion sensor will only activate the touch when there is a finger swipe and not, for example, when talking on the phone.

How a proximity sensor works

But what is the real functioning of this device? The proximity or presence 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 set to return, depending on the intensity used, it will be possible to understand at what distance the object is, so the sensor will be activated or not. The proximity sensor could be compared, in a distant way, to the echo sounder on ships: it is measured precisely on the basis of the return of the wave echo.

Operation is virtually identical: based on the return, the sensor will measure the distance to the nearest object and activate the functions for which it has been programmed.

Different types for different uses

Of course, there are many models available of every proximity or presence sensor, as each type allows a different application. In fact, the development of this technology has gone through several stages and has made it possible to come up with really useful models used in every field. One only has to think of the smartphone that turns off the touch at the moment of proximity to the ear or the parking sensor in the car. 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 infrared: this technology is used to prevent interference with surrounding light.

The nominal sensitivity, i.e. the maximum the beam can reach under optimal conditions, is an impressive 50 metres. This technology is usually applied on the latest generation of smartphones.

Inductive proximity sensors

Questo tipo di sensore sfrutta la riluttanza, ovvero il fenomeno di riflesso che avviene quando un oggetto viene attraversato da onde elettromagnetiche. Hanno un campo di applicazione sicuramente meno diffuso, visto che per poter avere un riscontro ci deve essere un materiale che abbia delle proprietà ferromagnetiche.

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

Magnetic proximity sensors

This proximity sensor also exploits 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 depending on the magnetic field created.

They have very good sensitivity and very good signal switching speed, i.e. wave response. Their functioning is still driven by a magnet, so 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 relies on the electrical capacitance that can be developed by a capacitor. The switching of the signal, i.e. its interpretation and reception, is therefore due to the generated field.

They have a higher nominal 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 infrared sensors.

Ultrasonic proximity sensors

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

The functions of these objects are very customisable and allow for an incredible product, capable of having a truly incredible nominal range: we are talking about 10 metres and they can detect any type of object, composed of any material.

Use and applications in Machine Vision as well

As we have seen, the proximity or presence 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.

Depending on the object we need to detect, we will be able to tell which one is right for us or which one we are using. Sensors also have uses and applications in Machine Vision because, as we have to reconstruct images in three dimensions on a two-dimensional surface, the use of sensors is very useful in order to have an accurate detection of objects and also for dimensional control.

High technology allows many techniques to be developed and every device that enables Machine Vision has a motion sensor. The sensor technology allows greater and more precise detection than other objects, thus achieving an image 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 should remember that among the factors of choice we must evaluate above all the switching accuracy and the nominal range.

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