- These are sensors that operate without physical and mechanical contact. They operate through electric and magnetic fields, and optical sensors are also widely used. In this article, we will analyze all three types of sensors: optical, capacitive and inductive, and at the end we will do an experiment with an inductive sensor. By the way, people also call contactless sensors proximity switches, so don't be afraid if you see such a name ;-).

Optical sensor

So, a few words about optical sensors... The principle of operation of optical sensors is shown in the figure below

Barrier

Remember those scenes from movies where the main characters had to walk through optical beams without hitting any of them? If the beam touched any part of the body, an alarm was triggered.

The beam is emitted through some source. There is also a “beam receiver”, that is, the little thing that receives the beam. As soon as the beam is not on the beam receiver, a contact in it will immediately turn on or off, which will directly control the alarm or anything else at your discretion. Basically, the beam source and the beam receiver, correctly called the beam receiver “photodetector,” come in pairs.

Optical displacement sensors from SKB IS are very popular in Russia.

These types of sensors have both a light source and a photodetector. They are located directly in the housing of these sensors. Each type of sensor is a complete design and is used in a number of machines where increased processing accuracy is required, down to 1 micrometer. These are mainly machines with a system H and verbal P programmatic U board ( CNC), which work according to the program and require minimal human intervention. These non-contact sensors are built on this principle

These types of sensors are designated by the letter “T” and are called barrier. As soon as the optical beam was interrupted, the sensor was activated.

Pros:

• range can reach up to 150 meters
• high reliability and noise immunity

Minuses:

• at long sensing distances, precise adjustment of the photodetector to the optical beam is required.

Reflex

The reflex type of sensors is designated by the letter R. In these types of sensors, the emitter and receiver are located in the same housing.

The operating principle can be seen in the figure below

Light from the emitter is reflected from some light reflector (reflector) and enters the receiver. As soon as the beam is interrupted by any object, the sensor is triggered. This sensor is very convenient on conveyor lines when counting products.

Diffusion

And the last type of optical sensors is diffusion - designated by the letter D. They may look different:

The principle of operation is the same as that of a reflector, but here the light is already reflected from objects. Such sensors are designed for a short response distance and are unpretentious in their operation.

Capacitive and inductive sensors

Optics are optics, but inductive and capacitive sensors are considered the most unpretentious in their operation and very reliable. This is roughly what they look like

They are very similar to each other. The principle of their operation is associated with changes in magnetic and electric field. Inductive sensors are triggered when any metal is brought close to them. They don't bite on other materials. Capacitive ones react to almost any substance.

How does an inductive sensor work?

As they say, it’s better to see once than to hear a hundred times, so let’s do a little experiment with inductive sensor.

So, our guest is a Russian-made inductive sensor

We read what is written on it

Brand of VBI sensor blah blah blah blah, S – sensing distance, here it is 2 mm, U1 – version for temperate climates, IP – 67 – protection level(in short, the level of protection here is very steep), U b – voltage at which the sensor operates, here the voltage can be in the range from 10 to 30 Volts, I load – load current, this sensor can deliver a current of up to 200 milliamps to the load, I think this is decent.

On the reverse of the tag there is a connection diagram for this sensor.

Well, let's check out the sensor's performance? To do this, we attach the load. Our load will be an LED connected in series with a resistor with a nominal value of 1 kOhm. Why do we need a resistor? The moment the LED is turned on, it begins to frantically consume current and burns out. In order to prevent this, a resistor is placed in series with the LED.

We supply the brown wire of the sensor with plus from the power supply, and the blue wire with minus. I took the voltage to 15 Volts.

The moment of truth is coming... We bring it to work area sensor is a metal object, and our sensor immediately triggers, as evidenced by the LED built into the sensor, as well as our experimental LED.

The sensor does not respond to materials other than metals. A jar of rosin means nothing to him :-).

Instead of an LED, a logic circuit input can be used, that is, when the sensor is triggered, it produces a logical one signal, which can be used in digital devices.

Conclusion

In the world of electronics, these three types of sensors are increasingly wide application. Every year the production of these sensors is growing and growing. They are used in completely different areas of industry. Automation and robotization would not be possible without these sensors. In this article, I analyzed only the simplest sensors that give us only an “on-off” signal, or, to put it in professional language, one bit of information. More sophisticated types of sensors can produce various parameters and can even connect to computers and other devices directly.

Buy an inductive sensor

In our radio store, inductive sensors cost 5 times more than if they were ordered from China from Aliexpress.

Here You can look at the variety of inductive sensors.

First of all, it is necessary to make a distinction between the concepts of “sensor” and “sensor”. A sensor is traditionally understood as a device capable of converting the input influence of any physical quantity into a signal convenient for further use. Today there are a number of requirements for modern sensors:

• Unambiguous dependence of the output value on the input value.
• Stable readings regardless of time of use.
• High sensitivity.
• Small size and light weight.
• No influence of the sensor on the controlled process.
• Ability to work in various conditions.
• Compatible with other devices.

Any sensor includes the following elements: a sensitive element and a signaling device. In some cases, an amplifier and signal selector may be added, but often there is no need for them. The components of the sensor also determine the principle of its further operation. At the moment when any changes occur in the object of observation, they are recorded by the sensitive element. Immediately after this, the changes are displayed on the alarm device, the data of which is objective and informative, but cannot be processed automatically.

Rice. 22.

An example of a simple sensor is a mercury thermometer. Mercury is used as a sensitive element, the temperature scale acts as a signaling device, and the object of observation is temperature. It is important to understand that the sensor readings are a set of data, not information. They are not saved to external or internal memory and are not suitable for automated processing, storage or transmission.

All sensors used by various technological solutions from the Internet of Things can be divided into several categories. One of the most convenient classifications is based on the purpose of devices "3:

• presence and motion sensors;
• position, movement and level detectors;
• speed and acceleration sensors;
• force and touch sensors;
• Pressure Sensors;
• flow meters;
• acoustic sensors;
• humidity sensors;
• light radiation detectors;
• temperature sensors;
• chemical and biological sensors.

The operation of sensors is very different from the operation of sensors. First of all, it is necessary to dwell on the definition of the concept “sensor”. A sensor is a device capable of converting changes that have occurred in an object of observation into an information signal suitable for further storage, processing and transmission.

The sensor operation circuit is close to the circuit characteristic of the sensor. In a certain sense, the sensor can be interpreted as an improved sensor, since its structure can be expressed as “component elements of the sensor” + “information processing unit”. The functional diagram of the sensor is as follows.

Rice. 23.

In this case, the classification of sensors by purpose is equivalent to the same classification for sensors. Often, sensors and transducers can measure the same value for the same object, but the sensors will display the data, and the sensors will also convert it into an information signal.

In addition, there is a special type of sensors that makes sense to consider to understand the concept of the Internet of Things. These are the so-called “smart” sensors, functional diagram which are complemented by the presence of algorithms for the primary processing of collected information. Thus, a conventional sensor is capable of processing data and providing it in the form of information, and a “smart” sensor is capable of performing any actions with independently captured information from the external environment.

In the future, we can expect serious development of 3D sensors capable of scanning the surrounding space with high accuracy and building a virtual model of it. Thus, the Capri 3D sensor is currently capable of detecting people’s movements and their metric characteristics.

teristics. In addition, this sensor can scan an object in the external environment and save the information in an SAE file for further sending for printing on a ZE printer.

Rice. 24. Capri 3D sensor connected to Samsung Nexus 10

The development of devices that combine several sensors at once deserves special attention. different types. As stated in paragraph 2.2.1, to obtain knowledge, information about various characteristics of an object is required. And the use of different sensors allows you to obtain the necessary information. In a sense, such devices can actually recognize people. An example of such a device is the Kinekt wireless controller, used in modern video games.

IR Emitter Color Sensor

Microphone Ar ray

Rice. 25. Kinekt 57 wireless controller device

The Kinekt controller contains several components: an infrared emitter; infrared receiver; color camera;

a set of 4 microphones and an audio signal processor; tilt correction tool.

Operating principle of the Klpek controller! simple enough. The rays leaving the infrared emitter are reflected and hit the infrared receiver. Due to this, it is possible to obtain information about the spatial position of the person playing the video game. The camera is able to capture various color data, and the microphones are able to pick up the player's voice commands. As a result, the controller is able to collect enough information about the person so that he can control the game through movements or voice commands.

In a sense, the Ktek controller! belongs to the field of Internet of Things technologies. It is able to identify the player, collect information about him and transfer it to other devices (game console). But a similar set of sensors can potentially be used in other areas that are promising for the Internet of Things concept, including the deployment of smart home technologies.

The types of sensors and their names are determined by the use of various ultrasonic transducers and scanning methods in them. Depending on the type of converters, we can distinguish:

● sector mechanical sensors(sector mechanical probe) - with single-element or multi-element annular grids;

● linear sensors with multi-element linear arrays;

● convex and microconvex sensors(convex or microconvex probe) - with convex and microconvex grilles, respectively;

● phased sector sensors(phased array probe) - with multi-element linear arrays;

● sensors with two-dimensional grid th, linear, convex and sector.

Here we have named the main types of sensors, without specifying their medical purpose, operating frequency and design features.

In sector mechanical sensors (Fig. 2.11 a, 2.11 b), the working surface (protective cap) covers the volume in which there is a single-element or ring ultrasonic transducer moving along the corner. The volume under the cap is filled with an acoustically transparent liquid to reduce losses during the passage of ultrasonic signals. The main characteristic of sector mechanical sensors, in addition to the operating frequency, is angular size scanning sector, which is indicated in the sensor marking (sometimes the length of the corresponding arc H is additionally given work surface). Marking example: 3.5 MHz/90°.

In linear, convex, microconvex and phased (sector) electronic scanning sensors, the working surface coincides with the emitting surface of the transducer, which is called aperture, and is equal to it in size. The characteristic sizes of apertures are used in sensor markings and help determine the choice of sensor.

In linear sensors, the aperture length L is typical (Fig. 2.11 c), since it is this that determines the width of the rectangular viewing area. Example of marking for a 7.5 MHz/42 mm linear sensor.

It should be borne in mind that the width of the viewing area in a linear sensor is always less than 20-40% of the aperture length. Thus, if the aperture size is specified as 42 mm, the width of the viewing area is no more than 34 mm.

In convex sensors, the viewing area is determined by two characteristic dimensions - the length of the arc H (sometimes its chord), corresponding to the convex working part, and the angular size of the scanning sector α in degrees Fig. 2.11 d. An example of convex sensor marking: 3.5 MHz/60°/ 60 mm. Use radius less often for marking R curvature of the working surface, for example:

3.5 MHz/60 R(radius - 60 mm).

Rice. 2.11. The main types of sensors for external inspection: a, b-

sector mechanical (a – cardiological, b – water

nozzle); c – linear electronic; g – convex;

d – microconvex; e – phased sector

In microconvex sensors, R is the characteristic radius of curvature of the working surface (aperture); sometimes the arc angle α is additionally given, which determines the angular size of the viewing sector (Fig. 2.11e). Marking example: 3.5 MHz/20R (radius - 20 mm).

For a phased sector sensor, the angular size of the electronic scanning sector is given in degrees. Marking example: 3.5 MHz/90°.

Shown in Fig. 2.11 sensors are used for external inspection. In addition to them, there are a large number of intracavitary and highly specialized sensors.

It is advisable to introduce a classification of sensors according to areas of medical application.

1. Universal sensors for external inspection(abdominal probe). Universal sensors are used to examine the abdominal region and pelvic organs in adults and children.

2. Sensors for superficial organs(small parts probe). Used to study shallowly located small organs and structures (for example, the thyroid gland, peripheral vessels, joints)

3. Cardiac sensors(cardiac probe). To study the heart, sector-type sensors are used, which is due to the peculiarity of observation through the intercostal gap. Mechanical scanning sensors (single-element or with a ring array) and phased electronic sensors are used.

4. Sensors for pediatrics(podiatric probes). For pediatric patients, the same sensors are used as for adults. , but only with a higher frequency (5 or 7.5 MHz), which allows you to get more high quality images. This is possible due to the small size of the patients.

5. Intracavitary sensors(intracavitary probes). There is a wide variety of intracavity sensors, which differ in their areas of medical application.

● Transvaginal (intravaginal) sensors (transvaginal or edovaginal probe).

● Transrectal or endorectal probe.

● Intraoperative probes.

● Transurethral probes.

● Transesophageal probes.

● Intravascular probes.

6. Biopsy or puncture probes(biopsy or puncture probes). Used for precise guidance of biopsy or puncture needles. For this purpose, sensors are specially designed in which the needle can pass through a hole (or slot) in the working surface (aperture).

7. Highly specialized sensors. Most of the sensors mentioned above have a fairly wide range of applications. At the same time, a group of sensors with narrow applications can be distinguished, and special mention should be made of them.

● Ophthalmology probes.

● Sensors for transcranial probes.

● Sensors for diagnosing sinusitis, sinusitis and sinusitis.

● Sensors for veterinary medicine (veterinary probes).

8. Broadband and multi-frequency sensors. Broadband sensors are increasingly used in modern complex devices. These sensors are designed similarly to the conventional sensors discussed above and differ from them in that they use a broadband ultrasonic transducer, i.e. sensor with a wide operating frequency band.

9. Doppler sensors. Sensors are used only to obtain information about the speed or spectrum of blood flow speeds in the vessels. These sensors are described in the sections devoted to Doppler ultrasound devices.

10. Sensors for 3D imaging. Special sensors for obtaining 3D (three-dimensional) images are rarely used. Conventional two-dimensional image sensors are more often used together with special devices, providing scanning along the third coordinate.

The quality of the information obtained depends on the technical level of the device - the more complex and advanced the device, the higher the quality of diagnostic information. As a rule, according to the technical level, devices are divided into four groups: simple devices; middle class devices; high-end devices; high-end (sometimes called high-end) devices.

There are no agreed upon criteria for assessing the class of devices among manufacturers and users of ultrasound diagnostic equipment, since there are a very large number of characteristics and parameters by which devices can be compared with each other. Nevertheless, it is possible to evaluate the level of complexity of the equipment, on which the quality of the information obtained largely depends. One of the main technical parameters that determine the level of complexity of an ultrasonic scanner is the maximum number of receiving and transmitting channels in the electronic unit of the device, since what larger number channels, the better the sensitivity and resolution - the main characteristics of ultrasound image quality.

In simple (usually portable) ultrasonic scanners, the number of transmission and reception channels is no more than 16, in medium and high-end devices - 32, 48 and 64. In high-class devices, the number of channels can be more than 64, for example 128, 256, 512 and even more. As a rule, high-end and high-end ultrasound scanners are devices with color Doppler mapping.

High-end instruments typically take full advantage of modern digital signal processing capabilities, starting right down to the sensor output. For this reason, such devices are called digital systems or platforms.

Control questions

1. What is acoustic impedance and its effect on reflection

ultrasound?

2. How does the attenuation of ultrasound in biological tissues depend on frequency?

3. How does the spectrum of a pulsed ultrasonic signal change with depth?

4. What operating modes are provided in ultrasound scanners?

5. What is the operating mode? IN?

6. What is the operating mode? A?

7. What is the operating mode? M?

8. What is the operating mode? D?

9.Explain the operation of the ultrasonic transducer.

10. What configurations of piezoelements are found in different types

sensors?

11. What types of sensors exist in ultrasound scanners?

In automation systems, the sensor is designed to convert a controlled or controlled quantity (parameter of a controlled object) into an output signal that is more convenient for the further movement of information. Therefore, the sensor is often called a converter, although this term is too general, since any element of automation and telemechanics, having an input and output, is to one degree or another a converter.

In the simplest case, the sensor carries out only one transformation Y=f(X), such as, for example, force in movement (in a spring), or temperature into electromotive force (in a thermoelement), etc. This type of sensor is called direct conversion sensors. However, in a number of cases it is not possible to directly influence the input value X on the required input value U (if such a connection is inconvenient or it does not provide the desired qualities). In this case, successive transformations are carried out: the input value X influences the intermediate Z, and the value Z influences the required value Y:

Z=f1(X); Y=f2(Z)

The result is a function connecting X to Y:

Y=f2=F(X).

The number of such successive transformations may be more than two, and in the general case, the functional connection between Y and X can pass through a number of intermediate quantities:

Y=fn(...)=F(X).

Sensors that have such dependencies are called sensors with serial conversion. All other parts are called intermediate bodies. In a sensor with two transformations there are no intermediate organs; it only has a sensing and an actuating organ. Often the same structural element performs the functions of several organs. For example, an elastic membrane performs the function of a sensing organ (converting pressure into force) and the function of an executive organ (converting force into displacement).

Classification of sensors.

The exceptional variety of sensors used in modern automation necessitates their classification. Currently, the following types of sensors are known, which are most appropriately classified according to the input value that practically corresponds to the principle of operation:

Sensor name	Input quantity
Mechanical	Moving a Rigid Body
Electric	Electrical quantity
Hydraulic	Moving Fluid
Pneumatic	Gas movement
Thermal
Optic	Luminous magnitude
Acoustic	Sound magnitude
Radio wave	Radio waves
	Nuclear radiation

Here we consider the most common sensors in which at least one of the quantities (input or output) is electrical.

Sensors are also distinguished by the range of variation of the input signal. For example, some electrical temperature sensors are designed to measure temperatures from 0 to 100°C, while others are designed to measure temperatures from 0 to 1600°C. It is very important that the range of variation of the output signal is the same (unified) for different devices. Unification of sensor output signals allows the use of common amplifying and actuating elements for the most different systems automation.

Electrical sensors are among the most important elements automation systems. With the help of sensors, the controlled or controlled quantity is converted into a signal, depending on the change in which the entire control process takes place. The most widely used sensors in automation are sensors with an electrical output signal. This is explained primarily by the convenience of transmitting an electrical signal over a distance, its processing and the possibility of converting electrical energy into mechanical work. In addition to electrical ones, mechanical, hydraulic and pneumatic sensors have become widespread.

Electrical sensors, depending on the principle of the transformation they produce, are divided into two types - modulators and generators.

For modulators (parametric sensors), the input energy affects the auxiliary electrical circuit, changing its parameters and modulating the value and nature of the current or voltage from an external energy source. Due to this, the signal received at the sensor input is simultaneously amplified. The presence of an external source of energy is prerequisite operation of sensors - modulators.

Rice. 1. Functional blocks of the sensor - modulator (a) and sensor - generator (b).

Modulation is carried out by changing one of three parameters - ohmic resistance, inductance, capacitance. In accordance with this, groups of ohmic, inductive and capacitive sensors are distinguished.

Each of these groups can be divided into subgroups. Thus, the most extensive group of ohmic sensors can be divided into subgroups: strain gauges, potentiometers, thermistors, photoresistors. The second subgroup includes options for inductive sensors, magnetoelastic and transformer. The third subgroup combines various types of capacitive sensors.

The second type - sensor-generators are simply converters. They are based on the emergence of electromotive force under the influence various processes associated with the controlled variable. The occurrence of such an electromotive force can occur, for example, as a result of electromagnetic induction, thermoelectricity, piezoelectricity, photoelectricity and other phenomena that cause separation of electrical charges. According to these phenomena, generator sensors are divided into induction, thermoelectric, piezoelectric and photoelectric.

Groups of electrical, electrostatic, Hall sensors, etc. are also possible.

Potentiometric and strain gauge sensors.

Potentiometric sensors are used to convert angular or linear movements into an electrical signal. The potentiometric sensor is variable resistor, which can be switched on using a rheostat circuit or a potentiometer (voltage divider) circuit.

Structurally, a potentiometric sensor is an electromechanical device (Fig. 2-1), consisting of a frame 1 with a thin wire (winding) wound on it from alloys with high resistivity, a sliding contact - brush 2 and a current conductor 3, made in the form of either a sliding contact or a spiral spring.

The frame with the wound wire is fixed motionless, and the brush is mechanically connected to the moving part of the op-amp, the movement of which must be converted into an electrical signal. When the brush moves, the active resistance Rx of the wire section between the brush and one of the terminals of the sensor winding changes.

Depending on the sensor connection circuit, movement can be converted into a change in active resistance or current (with sequential circuit switching on) or a change in voltage (when switching on using a voltage divider circuit). On the conversion accuracy at sequential connection significant influence has a change in the resistance of the connecting wires, the transition resistance between the brush and the sensor winding.

In automation devices, the inclusion of potentiometric sensors using a voltage divider circuit is more often used. When moving the moving part of the op-amp one-sidedly, a single-cycle switching circuit is used, which gives an irreversible static characteristic. For bilateral movement, a push-pull switching circuit is used, which gives a reversible characteristic (Fig. 2-2).

Depending on the design and functional law connecting the output signal of the sensor with the movement of the brush, several types of potentiometric sensors are distinguished.

Linear potentiometric sensors.

They have the same frame cross-section along the entire length. The wire diameter and winding pitch are constant. In idle mode (with load Rn→∞ and I→0), the output voltage of the linear potentiometric sensor Uout is proportional to the movement of the brush x: Uout = (U0/L)x, where U0 is the sensor supply voltage; l-winding length. The sensor supply voltage U0 and winding length L are constant values, therefore in the final form: Uout = kx, where k=U0/L is the transmission coefficient.

Functional potentiometric sensors.

They have a functional nonlinear relationship between brush movement and output voltage: Uout= f(x). Functional potentiometers with trigonometric, power or logarithmic characteristics are often used. Functional potentiometers are used in analog automatic computing devices, in float liquid level meters for complex tanks geometric shape etc. You can obtain the required functional dependence from potentiometric sensors various methods: by changing the height of the potentiometer frame (smoothly or stepwise), bypassing sections of the potentiometer winding with resistors.

Multi-turn potentiometric sensors.

They are a structural variation of linear potentiometric sensors with angular movement of the brush. With multi-turn sensors, the brush must rotate 360° several times in order to move the entire winding length L. The advantages of multi-turn sensors are high accuracy, low sensitivity threshold, small dimensions, disadvantages - relatively large friction torque, design complexity, presence of several sliding contacts

and difficulty of use in high-speed systems.

Metal film potentiometric sensors.

This is a new promising design of potentiometric sensors. Their frame is

a glass or ceramic plate on which a thin layer (several micrometers) of metal with high resistivity is applied. The signal from metal-film potentiometric sensors is collected using metal-ceramic brushes. Changing the width of the metal film or its thickness allows you to obtain a linear or nonlinear characteristic of the potentiometric sensor without changing its design. Using electronic or laser beam, you can automatically adjust the sensor resistance and its characteristics to the specified values. The dimensions of metal-film potentiometric sensors are significantly smaller than wire sensors, and the sensitivity threshold is practically zero due to the absence of winding turns.

When evaluating potentiometric sensors, it should be noted that they have both significant advantages and major disadvantages. Their advantages are: simplicity of design; high level output signal (voltage - up to several tens of volts, current - up to several tens of milliamps); opportunity to work both permanently and alternating current. Their disadvantages are: insufficiently high reliability and limited durability due to the presence of sliding contact and abrasion of the winding; influence on the load resistance characteristics; energy losses due to power dissipation by the active resistance of the winding; a relatively large torque required to rotate the moving part of the sensor with the brush.

Often a radio element such as a reed switch finds its application in electronics. Its peculiarity is the ability to close contacts when irradiated by a magnetic field. What does this mean? By taking a simple magnet or placing an electromagnet near the reed switch, you can easily close and open the contacts of this radio element. At its core, it is a kind of non-contact sensor.

Definition of the concept

What is a contactless sensor? It is understood as an electronic device that registers the presence of a certain object in its coverage area and operates without any mechanical or any other influences.

Non-contact sensors are used in the most various fields. This includes the creation of household appliances and facility security systems, industrial technologies and the automotive industry. By the way, this element is popularly called a “contactless switch.”

Advantages

Among the main advantages of contactless sensors are:

Compact dimensions;

High degree of tightness;

Durability and reliability;

Light weight;

Variety of installation options;

No contact with the object and no feedback.

Classification

There are different types of proximity sensors. They are classified according to the principle of action and are:

Capacitive;

Optical;

Inductive;

Ultrasonic;

Magnetosensitive;

Pyrometric.

Let's consider each of these types of devices separately.

Capacitive sensors

These devices are based on the measurement of electrical capacitors. Their dielectric contains the object that is subject to registration. The purpose of these types of contactless sensors is to work with a variety of applications. This is, for example, gesture recognition. Car rain sensors are produced as capacitive ones. Such devices remotely measure the liquid level during processing various materials etc.

The capacitive proximity sensor is an analog system that operates at a distance of up to seventy centimeters. Unlike other types of similar devices, it has greater accuracy and sensitivity. After all, the change in capacitance in it occurs in only a few picofarads.

Contactless sensor circuit of this type includes plates consisting of conductive printed circuit board, as well as charging. In this case, a capacitor is formed. Moreover, this will happen at any time either in a conductive grounded element or in some object whose dielectric constant is different from air. Such a device will also work if a person or part of his body appears in the device’s coverage area, which will be similar to the ground potential. As the finger approaches, for example, the capacitance of the capacitor will change. And even taking into account the fact that the system is nonlinear, it will not be difficult for it to detect a foreign object that has arisen within the boundaries being viewed.

The connection diagram for such a contactless sensor can be complicated. The device can use several elements independent of each other in the left/right, as well as down/up directions. This will expand the capabilities of the device.

Optical sensors

Such contactless switches today find their wide application in many branches of human activity, where the equipment necessary for detecting objects operates. When connecting a contactless sensor, coding is used. This allows you to prevent false operation of the device due to extraneous influence of light sources. Similar sensors also work when low temperatures. Under these conditions, thermal casings are put on them.

What are optical unsupervised sensors? This is an electronic circuit that responds to changes in the light flux that falls on the receiver. This principle of operation makes it possible to record the presence or absence of an object in a particular spatial area.

The design of optical contactless sensors has two main blocks. One of them is the radiation source, and the second is the receiver. They can be located in the same or in different buildings.

When considering the principle of operation of a contactless sensor, three types of optical devices can be distinguished:

1. Barrier. Optical switches of this type (T) operate on a direct beam. In this case, the devices consist of two individual parts- transmitter and receiver located coaxially relative to each other. The radiation flux emitted by the emitter must be directed exactly to the receiver. When the beam is interrupted by an object, the switch is activated. Such sensors have good noise immunity. In addition, they are not afraid of raindrops, dust, etc.
2. Diffuse. The operation of type D optical switches is based on the use of a beam reflected from an object. The receiver and transmitter of such a device are located in one housing. The emitter directs the flow to the object. The beam, reflected from its surface, is distributed in different directions. In this case, part of the flow returns back, where it is captured by the receiver. As a result, the switch trips.
3. Reflex. Such optical proximity sensors are type R. They use a beam reflected from a reflector. The receiver and emitter of such a device are also located in the same housing. When the beam hits the reflector, it is reflected and ends up in the receiver area, as a result of which the device is triggered. Such devices operate at a distance to the object of no more than 10 meters. Perhaps they can be used for fixing translucent objects.

Inductive sensors

At the heart of the work of this device lies the principle of taking into account changes in the inductance of its main components - the coil and the core. This is where the name of such a sensor comes from.

Changes in induction indicate that a metal object has appeared in the magnetic field of the coil, which has changed it and, accordingly, the entire connection circuit, the main function of which is assigned to the comparator. In this case, a signal is sent to the relay and the electric current is turned off.

Based on this, we can talk about the main purpose of such a device. It is used to measure the movement of a piece of equipment that must be shut down if the movement limits are exceeded. The sensors themselves have motion boundaries ranging from one micron to twenty millimeters. In this regard, such a device is also called an inductive position switch.

A review of contactless sensors of this type allows us to distinguish several varieties. Similar classification based on different numbers of connection wires:

1. Two-wire. Such inductive sensors are connected directly to the circuit. This is the simplest, but at the same time quite capricious option. It requires a rated load resistance. If this indicator decreases or increases, the operation of the device becomes incorrect.
2. Three-wire. Similar view The induction sensor is the most common. In such circuits, two wires should be connected to the voltage, and one wire should be connected directly to the load.
3. Four- and five-wire. In these sensors, two wires are connected to the load, and the fifth is used to select the required operating mode.

Ultrasonic sensors

These devices are widely used in a wide variety of production areas, solving many automation problems. technological cycles. Ultrasonic proximity sensors are used to determine the location and distance of various objects.

For example, they are used to detect labels, even transparent ones, to measure distances and control the movement of an object. They are used to determine the liquid level. The need for this arises, for example, to take into account fuel consumption when performing transport work. And these are just a few of the many applications for ultrasonic switches.

Such sensors are quite compact. They are distinguished by high-quality construction and the absence of various moving parts. This equipment is not afraid of contamination, which is quite important in industrial conditions, and also requires almost no maintenance.

The ultrasonic sensor contains a piezoelectric heater, which is both an emitter and a receiver. This structural part reproduces a stream of sound pulses, receiving it and converting the received signal into voltage. Next, it is fed to the controller, which processes the data and calculates the distance at which the object is located. Similar technology called echolocation.

The active range of an ultrasonic sensor is the operating detection range. This is the distance within which the ultrasonic device can “see” an object, regardless of whether it is approaching the sensing element in the axial direction or moving across the sound cone.

Depending on the principle of operation, ultrasonic sensors are distinguished:

1. Provisions. Such devices are used to calculate the time interval required for sound to travel from a device to a particular object and back. Non-contact ultrasonic position sensors are used to monitor the location and presence of various mechanisms, as well as to count them. Such devices are also used as level indicators for various liquids or bulk materials.
2. Distances and movements. The operating principle of such devices is similar to that used in the device described above. The only difference is the type of signal that is present at the output. It is analog, not discrete. Sensors of this type are used to convert existing indicators of the distance to an object into certain electrical signals.

Magnetic sensors

These switches are used for position control. The sensors are triggered when a magnet, which is located on a moving part of the mechanism, approaches. Such devices have an extended temperature range (from -60 to +125 degrees Celsius). This functionality allows you to automate a large number of complex production processes.

Non-contact temperature sensor of magnetically sensitive type is used:

In chemical and metallurgical industries;

In the regions of the Far North;

On rolling stock;

In refrigeration units;

On truck cranes;

They are used in building security systems, as well as for automatically opening windows and entrance doors.

The most modern and fast-acting are magnetically sensitive sensors that operate on the Hall effect. They are not subject to mechanical wear, as they have an electronic output switch. The resource of such sensors is practically unlimited. In this regard, their use is beneficial and practical solution tasks of measuring the number of shaft revolutions, fixing the location of fast moving objects, etc.

When measuring liquid levels, float-type magnetically sensitive sensors are widely used. They are the best option for determining the required indicators due to their inexpensive price and simplicity of design.

Microwave sensors

This type of contactless switches is the most universal design option, which can be achieved by continuous scanning of the serviced area. It is worth keeping in mind that they are in a higher price category than, for example, ultrasonic analogues.

The functioning of such a device occurs due to the radiation of electromagnetic waves having high frequency, the meaning of which is slightly different in devices from different manufacturers. Microwave sensors are configured to scan and receive reflected waves. This allows the device to record even the slightest changes in the electromagnetic background. If this happens, the warning system connected to the sensor is immediately triggered in the form of an alarm, lighting, etc.

Microwave devices have increased operating accuracy and sensitivity. They are not barriers brick walls, doors and furniture. This fact should be taken into account when installing the system. The sensitivity level of the device can be changed by setting the motion sensor.

Microwave switches are used to control indoor and outdoor lighting, alarm devices, electrical appliances, etc.

Pyrometric sensors

The body of any living creature is characterized by the presence of thermal radiation, which is a beam electromagnetic waves different lengths. As the body's temperature rises, the amount of energy it emits also increases.

Sensors called pyrometric sensors operate based on the detection of thermal radiation. They are:

Total radiation, measuring total thermal energy bodies;

Partial radiation, measuring the energy of the area limited by the receiver;

Spectral ratios, which provide an indicator of the energy ratio of certain parts of the spectrum.

Non-contact sensors are most often used in devices that record the movement of objects.

Touch switches

Developing technologies have affected almost all spheres of human activity. They also did not ignore the issues of home improvement. One striking example of this is the touch switch. This device allows you to control room lighting with a light touch.

The touch switch responds immediately even with the slightest touch of the button. Its design includes three main elements. Among them:

1. A control unit that processes the received signal and transmits it the necessary elements.
2. Switching device. This part closes and opens the circuit, and also changes the current consumed by the lamp.
3. Control (touch) panel. Using this part, the switch receives signals from the remote control or from touch. The most modern devices are activated when you hold your hand near them.

Standard models can:

Turn lights on and off;

Adjust brightness;

Monitor the operation of heating devices, reporting temperature changes;

Open and close blinds;

Turn household devices on and off.

Touch switches produce various types. The specific model is selected depending on the needs of an office or residential building. For example, the desire to purchase and install a touch device may arise due to the location of a fixed switch in in an inconvenient place with the impossibility of transferring it. Or maybe there is a person living in a house or apartment whose mobility is limited. Sometimes stationary switches are located at such a height that they are inaccessible to children. Solving a problem will require choice. a certain model. Some owners prefer to install touch switches to change the brightness of the light without getting out of bed, etc.