Sensors types operating principle. Electronic sensors. Buy inductive sensor

Sensors are complex devices that are often used to detect and respond to electrical or optical signals. The device converts a physical parameter (temperature, blood pressure, humidity, speed) into a signal that can be measured by the device.

The classification of sensors in this case can be different. There are several basic parameters for the distribution of measuring devices, which will be discussed further. Basically, this separation is due to the action of various forces.

This is easy to explain with the example of temperature measurement. Mercury in a glass thermometer expands and compresses the liquid to convert the measured temperature, which can be read by an observer from a calibrated glass tube.

Criterias of choice

There are certain features that need to be taken into account when classifying a sensor. They are listed below:

1. Accuracy.
2. Environmental conditions - usually sensors have limitations in temperature, humidity.
3. Range - sensor measurement limit.
4. Calibration is essential for most measuring instruments as readings change over time.
5. Price.
6. Repeatability - Variable readings are measured repeatedly in the same environment.

Category distribution

Sensor classifications fall into the following categories:

1. The primary input number of arguments.
2. Principles of transduction (use of physical and chemical effects).
3. Material and technology.
4. Appointment.

The principle of transduction is a fundamental criterion followed for effective information gathering. Typically, logistical criteria are selected by the development team.

The classification of sensors based on properties is distributed as follows:

1. Temperature: thermistors, thermocouples, resistance thermometers, microcircuits.
2. Pressure: Fiber Optic, Vacuum, Liquid Based Flexible Gauges, LVDT, Electronic.
3. Flow: electromagnetic, differential pressure, positional displacement, thermal mass.
4. Level sensors: differential pressure, ultrasonic radio frequency, radar, thermal displacement.
5. Proximity and displacement: LVDT, photovoltaic, capacitive, magnetic, ultrasonic.
6. Biosensors: resonant mirror, electrochemical, surface plasmon resonance, light-addressable potentiometric.
7. Image: Charge Coupled Devices, CMOS.
8. Gas and chemistry: semiconductor, infrared, conduction, electrochemical.
9. Acceleration: gyroscopes, accelerometers.
10. Others: humidity sensor, speed sensor, mass, tilt sensor, force, viscosity.

This is a large group consisting of subsections. It is noteworthy that with the discovery of new technologies, the sections are constantly updated.

Purpose of sensor classification based on direction of use:

1. Control, measurement and automation of the production process.
2. Non-industrial use: aviation, medical devices, automobiles, consumer electronics.

Sensors can be classified according to their power requirements:

1. Active sensor - devices that require power. For example, LiDAR (light detection and rangefinder), a photoconductive cell.
2. Passive sensor - sensors that do not require power. For example, radiometers, film photography.

These two sections include all devices known to science.

In current applications, the purpose of sensor classification can be grouped as follows:

1. Accelerometers - based on microelectromechanical sensor technology. They are used to monitor patients who turn on pacemakers. and dynamic systems of the vehicle.
2. Biosensors - based on electrochemical technology. Used to test food, medical devices, water and detect dangerous biological pathogens.
3. Image sensors - based on CMOS technology. They are used in consumer electronics, biometrics, traffic and security surveillance, and computer imaging.
4. Motion detectors - based on infrared, ultrasonic and microwave/radar technologies. Used in video games and simulations, light activation and security detection.

Sensor types

There is also a core group. It is divided into six main areas:

1. Temperature.
2. Infrared radiation.
3. Ultraviolet.
4. Sensor.
5. Approach, movement.
6. Ultrasound.

Each group may include subsections, if the technology is even partially used as part of a particular device.

1. Temperature sensors

This is one of the main groups. The classification of temperature sensors unites all devices that have the ability to evaluate parameters based on the heating or cooling of a particular type of substance or material.

This device collects temperature information from a source and converts it into a form that other equipment or people can understand. The best illustration of a temperature sensor is mercury in a glass thermometer. Mercury in glass expands and contracts with changes in temperature. The outdoor temperature is the starting element for measuring the indicator. The position of the mercury is observed by the viewer to measure the parameter. There are two main types of temperature sensors:

1. contact sensors. This type of device requires direct physical contact with the object or carrier. They control the temperature of solids, liquids and gases over a wide temperature range.
2. Contactless sensors. This type of sensor does not require any physical contact with the measured object or medium. They control non-reflective solids and liquids, but are useless for gases due to their natural transparency. These instruments use Planck's law to measure temperature. This law concerns the heat emitted by the source to measure the benchmark.

Working with various devices

The principle of operation and classification of temperature sensors are also divided into the use of technology in other types of equipment. These can be dashboards in a car and special production units in an industrial shop.

1. Thermocouple - modules are made of two wires (each - from different homogeneous alloys or metals), which form a measuring transition by connecting at one end. This measuring unit is open to the studied elements. The other end of the wire ends with a measuring device where a reference junction is formed. Current flows through the circuit because the temperatures of the two junctions are different. The resulting millivolt voltage is measured to determine the temperature at the junction.
2. Resistance temperature detectors (RTDs) are types of thermistors that are made to measure electrical resistance as temperature changes. They are more expensive than any other temperature detection devices.
3. Thermistors. They are another type of thermal resistor in which a large change in resistance is proportional to a small change in temperature.

2. IR sensor

This device emits or detects infrared radiation to determine the specific phase in the environment. As a rule, thermal radiation is emitted by all objects in the infrared spectrum. This sensor detects a type of source that is not visible to the human eye.

The basic idea is to use infrared LEDs to transmit light waves to an object. Another IR diode of the same type should be used to detect the reflected wave from the object.

Operating principle

Classification of sensors in the automation system in this direction is common. This is due to the fact that the technology makes it possible to use additional tools for assessing external parameters. When an infrared receiver is exposed to infrared light, a voltage difference develops across the wires. The electrical properties of the IR sensor components can be used to measure the distance to an object. When an infrared receiver is exposed to light, a potential difference develops across the wires.

Where applied:

1. Thermography: According to the law of the radiation of objects, it is possible to observe the environment with or without visible light using this technology.
2. Heating: infrared radiation can be used to cook and heat food. They can remove ice from aircraft wings. The converters are popular in the industrial field such as printing, plastic molding and polymer welding.
3. Spectroscopy: This technique is used to identify molecules by analyzing constituent bonds. The technology uses light radiation to study organic compounds.
4. Meteorology: measure the height of clouds, calculate the temperature of the earth and surface is possible if meteorological satellites are equipped with scanning radiometers.
5. Photobiomodulation: used for chemotherapy in cancer patients. Additionally, the technology is used to treat the herpes virus.
6. Climatology: monitoring the exchange of energy between the atmosphere and the earth.
7. Communication: An infrared laser provides light for optical fiber communication. These emissions are also used for short distance communication between mobile and computer peripherals.

3. UV sensor

These sensors measure the intensity or power of the incident ultraviolet radiation. A form of electromagnetic radiation has a longer wavelength than X-rays, but is still shorter than visible radiation.

An active material known as polycrystalline diamond is used to reliably measure ultraviolet. Instruments can detect various environmental impacts.

Device selection criteria:

1. Wavelength ranges in nanometers (nm) that can be detected by ultraviolet sensors.
2. Working temperature.
3. Accuracy.
4. power range.

Operating principle

The UV sensor receives one type of energy signal and transmits another type of signals. To observe and record these output streams, they are sent to an electric meter. To create graphs and reports, the indicators are transferred to an analog-to-digital converter (ADC), and then to a computer with software.

Used in the following devices:

1. UV phototubes are radiation-sensitive sensors that monitor UV air treatment, UV water treatment, and solar exposure.
2. Light sensors - measure the intensity of the incident beam.
3. Ultraviolet spectrum sensors are charge-coupled devices (CCDs) used in laboratory imaging.
4. UV detectors.
5. Bactericidal UV detectors.
6. Photostability sensors.

4. Touch sensor

This is another large group of devices. The classification of pressure sensors is used to assess the external parameters responsible for the appearance of additional characteristics under the action of a certain object or substance.

The touch sensor acts like a variable resistor according to where it is connected.

The touch sensor consists of:

1. A completely conductive substance such as copper.
2. Insulated intermediate material such as foam or plastic.
3. Partially conductive material.

However, there is no strict division. The classification of pressure sensors is established by choosing a specific sensor, which evaluates the emerging voltage inside or outside the object under study.

Operating principle

A partially conductive material opposes the flow of current. The principle of the linear encoder is that the current flow is considered to be more opposite when the length of the material through which the current is to pass is longer. As a result, the material's resistance is changed by changing the position in which it comes into contact with a fully conductive object.

The classification of automation sensors is based entirely on the described principle. Here, additional resources are involved in the form of specially developed software. Typically, software is associated with touch sensors. Devices can remember "last touch" when the sensor is disabled. They can register the "first touch" as soon as the sensor is activated and understand all the meanings associated with it. This action is similar to moving a computer mouse to the other end of the mouse pad to move the cursor to the far side of the screen.

5. Proximity sensor

Increasingly, modern vehicles are using this technology. The classification of electrical sensors using light and sensor modules is gaining popularity with automotive manufacturers.

The proximity sensor detects the presence of objects that are almost without any points of contact. Since there is no contact between the modules and the perceived object and there are no mechanical parts, these devices have a long service life and high reliability.

Different types of proximity sensors:

1. Inductive proximity sensors.
2. Capacitive proximity sensors.
3. Ultrasonic proximity sensors.
4. Photoelectric sensors.
5. Hall sensors.

Operating principle

The proximity sensor emits an electromagnetic or electrostatic field or a beam of electromagnetic radiation (such as infrared) and waits for a response signal or changes in the field. The object to be detected is known as the target of the registration module.

The classification of sensors according to the principle of operation and purpose will be as follows:

1. Inductive devices: there is an oscillator at the input that changes the loss resistance to the proximity of an electrically conductive medium. These devices are preferred for metal objects.
2. Capacitive Proximity Sensors: These convert the change in electrostatic capacitance between the detection electrodes and ground. This occurs when approaching a nearby object with a change in the oscillation frequency. To detect a nearby object, the oscillation frequency is converted into a DC voltage, which is compared to a predetermined threshold. These devices are preferred for plastic objects.

The classification of measuring equipment and sensors is not limited to the above description and parameters. With the advent of new models of measuring instruments, the general group is increasing. Various definitions have been approved to distinguish between sensors and transducers. Sensors can be defined as an element that senses energy in order to produce a variant in the same or a different form of energy. The sensor converts the measured value into the desired output signal using the conversion principle.

Based on the received and created signals, the principle can be divided into the following groups: electrical, mechanical, thermal, chemical, radiant and magnetic.

6. Ultrasonic sensors

An ultrasonic sensor is used to detect the presence of an object. This is achieved by emitting ultrasonic waves from the head of the device and then receiving the reflected ultrasonic signal from the corresponding object. It helps in detecting the position, presence and movement of objects.

Because ultrasonic sensors rely on sound rather than light for detection, they are widely used in water level measurements, medical scanning procedures, and in the automotive industry. Ultrasonic waves can detect invisible objects such as transparencies, glass bottles, plastic bottles and sheet glass with their reflective sensors.

Operating principle

The classification of inductive sensors is based on the scope of their use. Here it is important to take into account the physical and chemical properties of objects. The movement of ultrasonic waves differs depending on the shape and type of medium. For example, ultrasonic waves travel straight through a homogeneous medium and are reflected and transmitted back to the boundary between different media. The human body in the air causes significant reflection and can be easily detected.

The technology uses the following principles:

1. Multireflection. Multiple reflection occurs when waves are reflected more than once between the sensor and the target.
2. Limit zone. The minimum sensing distance and the maximum sensing distance can be adjusted. This is called the limit zone.
3. detection zone. This is the interval between the surface of the sensor head and the minimum detection distance obtained by adjusting the scan distance.

Devices equipped with this technology allow scanning of various types of objects. Ultrasonic sources are actively used in the creation of vehicles.

Until the 70th year of the last century, any car was equipped with a maximum of three sensors: fuel level, coolant temperature and oil pressure. They were connected to magnetoelectric and light indication devices on the instrument panel. Their purpose was only to inform the driver about the parameters of the engine and the amount of fuel. Then the device of car sensors was very simple.

But time passed, and in the 70s of the same century, car manufacturers began to reduce the content of harmful substances in the exhaust gases coming off their car conveyors. The car sensors necessary for this no longer reported anything to the driver, but only transmitted information about the operation of the engine to. Their total number in each car has increased significantly. The next decade was marked by the struggle for safety in the use of machines, for which new sensors were designed. They were intended for the operation of the anti-lock brake system and the deployment of airbags during traffic accidents.

ABS

This system is designed to prevent complete blocking of the wheels when braking. Therefore, the device necessarily contains wheel speed sensors. Their designs are different. They are either passive or active.

• Passive are mostly inductive sensors. The sensor itself consists of a steel core and a coil with a large number of turns of thin enameled copper wire. In order for it to perform its functions, a steel gear ring is pressed onto the wheel drive or hub. And the sensor is fixed so that when the wheel rotates, the teeth pass near the core and induce electrical impulses in the coil. Their repetition rate will be a proportional expression of the speed of rotation of the wheel. The advantages of this type of device are: simplicity, lack of power and low cost. Their disadvantage is that the pulse amplitude is too small at speeds up to 7 km/h.

• Active, which are of two types. Some are based on the well-known Hall effect. Others are magnetoresistive based on the phenomenon of the same name. The magnetoresistive effect consists in changing the electrical resistance of a semiconductor when it enters a magnetic field. Both types of active sensors are characterized by a sufficient amplitude of pulses at any speed. But their device is more complicated, and the cost is higher than passive ones. And the fact that they need food can not be called an advantage.

Lubrication system

Automotive sensors that control the parameters of this system are of three types:

Engine cooling

A car with a carburetor engine was equipped with two temperature sensors. One included an electric radiator fan to maintain operating temperature. The display device took readings from the other. The cooling system of a modern car equipped with an electronic engine control unit (ECU) also has two temperature sensors. One of them uses a coolant temperature display device in the instrument cluster. Another temperature sensor is required for the operation of the ECU. Their structure is fundamentally different. Both are NTC thermistors. That is, their resistance decreases with decreasing temperature.

intake tract

• Mass air flow sensor (DMRV). Designed to determine the volume of air entering the cylinders. This is necessary to calculate the amount of fuel to form a balanced air-fuel mixture. The knot consists of virgin platinum threads through which an electric current is passed. One of them is in the air flow entering the motor. The other, the reference one, is away from him. The currents passing through them are compared in the ECU. The difference between them determines the volume of air entering the motor. Sometimes, for greater accuracy, air temperature is taken into account.

• The intake manifold absolute pressure sensor, also called the MAP sensor. Used to determine the volume of air entering the cylinders. It can be an alternative to the DMRV for turbocharged engines. The device consists of a body and a ceramic diaphragm coated with a tensoresistive film. The volume of the body is divided by the diaphragm into 2 parts. One of them is sealed, and the air is pumped out of it. The other is connected by a tube to the intake manifold, so the pressure in it is equal to the pressure of the air injected into the engine. Under the action of this pressure, the diaphragm is deformed, which changes the resistance of the film on it. This resistance characterizes the absolute air pressure in the manifold.
• Throttle position sensor (TPS). Provides a signal proportional to the opening angle of the air damper. It is, in essence, a variable resistor. Its fixed contacts are connected to ground and to the reference voltage. And from the movable, mechanically connected to the axis of the throttle valve, the output voltage is removed.

Exhaust system

Oxygen sensor. This device plays the role of feedback to maintain the desired ratio of air and fuel in the combustion chambers. Its work is based on the principle of operation of a galvanic cell with a solid electrolyte. The latter is ceramics based on zirconium dioxide. The construction electrodes are platinum deposition on both sides of the ceramic. The device starts working after warming up to a temperature of 300 to 400 ◦ C.

Heating up to such a high temperature is usually carried out by hot exhaust gases or a heating element. Such a temperature regime is necessary for the occurrence of conductivity of the ceramic electrolyte. The presence of unburned fuel in the engine exhaust is the reason for the appearance of a potential difference on the electrodes of the sensor. Despite the fact that everyone is accustomed to calling this device an oxygen sensor, it is more of an unburned fuel sensor. Since the appearance of the output signal occurs when its surface comes into contact not with oxygen, but with fuel vapor.

Other sensors

The most important and most widely used technical means of automation are sensors.

sensor called the primary converter of a controlled or regulated value into an output signal, convenient for remote transmission and further use. The sensor consists of a perceiving (sensitive) organ and one or more intermediate transducers. Quite often, the sensor consists of only one receiving element (for example: thermocouple, resistance thermometer, etc.). The sensor is characterized by input and output values.

Change in the output value depending on the change in the input value

called sensor sensitivity;

A change in the output signal resulting from a change in the internal

properties of the sensor or changes in the external conditions of its operation - changes

ambient temperature, voltage fluctuations, etc. called sensor error;

The lag of changes in the output value from changes in the input value

called sensor inertia.

All these indicators of sensors must be taken into account when choosing sensors for automating a particular machine or process.

Sensors designed to measure physical (non-electrical input values ​​of humidity level, density, temperature, etc.) convert them into electrical output values ​​transmitted at a distance to act on the actuator.

Sensors are divided into:

- by appointment- measurement of movement of forces, temperature, humidity, speed

- according to the principle of action- electrical, mechanical, thermal, optical, and

- according to the method of transformation- non-electric quantity into electrical -

inductive, thermoelectric, photovoltaic, radioactive, active

resistances (potentiometric, tensometric, etc.).

Sensors are:

- contact(directly in contact);

- contactless(do not touch: photoelectric, ultrasonic,

radioactive, optical, etc.).

SCROLL

used in the construction industry to automate construction machines and technological processes, technical means of automation and automated control systems.

1. For control and information:

1.1 quality of compacted soil (density);

1.2 calculation of the amount of work performed (km traveled, water supplied, etc.);

1.3 the speed of the machine;

1.4 the presence of liquid in the container and its quantity;

1.5 the amount of bulk materials in the tank (cement, sand, crushed stone

2. For regulation:

2.1 maintaining the set temperature during concrete heating;

2.2 coolant thermostat of the internal combustion engine;

2.3 liquid pressure in the container (system);

2.4 pressure of gases (air) in the system (tank);

2.5 carrying capacity of lifting and other machines;

2.6 lifting height of the working body of the machine (crane boom, working platform,

hoists and elevators, loading skip, bucket, etc.);

2.7 lifting height of the load of the lifting machine;

2.8 rotation of the crane boom;

2.9 restriction of the movement of the machine along the tracks (tower or overhead crane, trolleys

2.10 limiting the approach to live wires (boom and

crane cable);

2.11 maintaining the specified level and slope of the bottom of the pit and trench during operation

excavator;

2.12 short circuit protection;

2.13 protection against overvoltage (undervoltage);

2.14 shutdown of all engines and fixing with grabs for the rails of the tower crane, depending on the wind speed.

3. For local automation of the control system:

3.1 engine operation mode depending on the load on the working body (bulldozer - dump deepening, scraper and grader - knife deepening, excavator - bucket deepening);

3.2 setting the doses of the components of the concrete mixture in accordance with the recipe;

3.3 dosing of constituent materials for the preparation of concrete mix;

3.4 determination of the duration and maintenance of this duration during the preparation of the concrete mix.

4. To automate the control system:

4.1 automated control system for the operation of a concrete mixing plant;

4.2 automated control system for a bulldozer - a set of "AKA-Dormash", "Combiplan-10 LP", when performing work at specified elevations, slope and direction;

4.3 automated motor grader control system - “Profile-20”,

”Profile-30” for road grading and territory planning;

4.4 automated scraper control system - “Kopir-Stabiplan-10” when excavating soil or vertical leveling to a given mark (altitude position of the bucket, moving the rear wall of the bucket, deepening (raising) the bucket knife and adjusting the tractor engine and its direction;

4.5 automated control system for a bucket-wheel excavator when developing trenches in a given direction, digging depth, a given slope of the trench bottom and regulating engine operation.

For a visual representation of an automated (automatic) system, graphic images are used:

Structural diagram, which reflects the improved structure of the system and the relationship between the points of control and management of objects;

Functional diagram, a drawing on which technological equipment, communications, controls and automation tools (instruments, regulators, sensors) are shown schematically with symbols, indicating the links between

technological equipment and automation elements. The diagram shows the parameters that are subject to control and regulation;

As well as principal, assembly and other schemes.

Electronic sensors (meters) are an important component in the automation of any technological processes and in the control of various machines and mechanisms.

With the help of electronic devices, you can get complete information about the parameters of the controlled equipment.

The principle of operation of any electronic sensor is based on the conversion of controlled indicators into a signal that is transmitted for further processing by the control device. It is possible to measure any quantities - temperature, pressure, electrical voltage and current strength, light intensity and other indicators.

The popularity of electronic meters is due to a number of design features, in particular, it is possible:

• transmit the measured parameters to almost any distance;
• convert indicators into a digital code to achieve high sensitivity and speed;
• transfer data at the highest possible speed.

According to the principle of operation, electronic sensors are divided into several categories depending on the principle of operation. Some of the most sought after are:

• capacitive;
• inductive;
• optical.

Each of the options has certain advantages that determine the optimal scope of its application. The principle of operation of any type of meter may vary depending on the design and the monitoring equipment used.

CAPACITIVE SENSORS

The principle of operation of an electronic capacitive sensor is based on a change in the capacitance of a flat or cylindrical capacitor, depending on the movement of one of the plates. Also taken into account is such an indicator as the dielectric constant of the medium between the plates. One of the advantages of such devices is a very simple design, which allows you to achieve good strength and reliability.

Also, meters of this type are not subject to distortion of indicators during temperature changes. The only condition for accurate performance is protection from dust, moisture and corrosion.

Capacitive sensors are widely used in a wide variety of industries. Easy-to-manufacture devices are characterized by low production cost, while they have a long service life and high sensitivity.

Depending on the design, the devices are divided into single-capacity and spirit-capacitive. The second option is more complicated to manufacture, but it is characterized by increased measurement accuracy.

Application area.

Most often, capacitive sensors are used to measure linear and angular displacements, and the design of the device may vary depending on the measurement method (the area of ​​the electrodes or the gap between them changes). To measure angular displacements, sensors with a variable area of ​​capacitor plates are used.

Capacitive transducers are also used to measure pressure. The design provides for the presence of one electrode with a diaphragm, which bends under the action of pressure, changing the capacitance of the capacitor, which is fixed by the measuring circuit.

Thus, capacitive meters can be used in any control and regulation systems. In energy, mechanical engineering, and construction, linear and angular displacement sensors are usually used. Capacitive level transmitters are most effective when handling bulk materials and liquids, and are often used in the chemical and food industries.

Electronic capacitive sensors are used to accurately measure air humidity, dielectric thickness, various deformations, linear and angular accelerations, ensuring accuracy in a variety of conditions.

INDUCTIVE SENSORS

Non-contact inductive sensors work on the principle of changing the inductance of a core coil. The key feature of this type of meters is that they only respond to changes in the location of metal objects. The metal has a direct effect on the electromagnetic field of the coil, which leads to the triggering of the sensor.

Thus, using an inductive sensor, you can effectively track the position of metal objects in space. This allows the use of inductive meters in any industry where monitoring of the position of various structural elements is required.

One of the interesting features of the sensor is that the electromagnetic field varies in different ways, depending on the type of metal, which somewhat expands the scope of the devices.

Inductive sensors have a number of advantages, of which the absence of moving parts deserves special attention, which significantly increases the reliability and strength of the structure. Also, sensors can be connected to industrial voltage sources, and the principle of operation of the meter guarantees high sensitivity.

Inductive sensors are made in several form factors, for the most convenient installation and operation, for example, dual meters (two coils in one housing).

Application area.

The scope of use of inductive meters is automation in any industry. A simple example - the device can be used as an alternative to a limit switch, while the response speed will be increased. Sensors are made in a dust and moisture protective housing for operation in the most difficult conditions.

Devices can be used to measure a wide variety of quantities - for this, converters of the measured indicator into the displacement value are used, which is fixed by the device.

OPTICAL SENSORS

Non-contact electronic optical sensors are one of the most popular types of meters in industries that require efficient positioning of any objects with maximum accuracy.

The principle of operation of this type of meters is based on fixing the change in the luminous flux when an object passes through it. The simplest device circuit is an emitter (LED) and a photodetector that converts light radiation into an electrical signal.

In modern optical meters, a modern electronic coding system is used, which makes it possible to exclude the influence of extraneous light sources (protection against false positives).

Structurally, optical meters can be performed both in separate housings for the emitter and receiver, or in one, depending on the principle of operation of the device and its field of application. The case additionally provides protection against dust and moisture (special thermal casings are used for operation at low temperatures).

Optical sensors are classified depending on the scheme of operation. The most common type is barrier, consisting of an emitter and a receiver located strictly opposite each other. When the constant light output is interrupted by an object, the device gives a corresponding signal.

The second popular type is a diffuse optical meter, in which the emitter and photodetector are located in the same housing. The principle of operation is based on the reflection of the beam from the object. The reflected light flux is captured by a photodetector, after which the electronics are triggered.

The third option is a reflective optical sensor. As in a diffuse meter, the emitter and receiver are structurally made in the same housing, but the light flux is reflected from a special reflector.

Usage.

Optical sensors are widely used in automated control systems and serve to detect objects and count them. The relatively simple design ensures reliability and high measurement accuracy. The coded light signal provides protection from external factors, and the electronics allows you to determine not only the presence of objects, but also determine their properties (dimensions, transparency, etc.).

Optical devices are widely used in security systems, where they are used as effective motion sensors. Regardless of the type, electronic sensors are the best option for modern control systems and automatic equipment.

The high accuracy and speed of measurement ensure the proper functioning of the equipment with minimal deviations. At the same time, most electronic meters are non-contact, which increases the reliability of devices several times and guarantees a long service life even in difficult production conditions.

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The materials presented on the site are for informational purposes only and cannot be used as guidelines and normative documents.

- these are sensors that work without physical and mechanical contact. They work through an electric and magnetic field, 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, the 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

Do you remember any shots from films where the main characters had to go through optical beams and not hit any of them? If the beam was touched by any part of the body, an alarm was triggered.

The beam is emitted by some source. And there is also a “beam receiver”, that is, the thing that receives the beam. As soon as there is no beam on the beam receiver, the contact will immediately turn on or off in it, which will directly control the alarm or something else at your discretion. Basically, a beam source and a receiver, properly called a "photodetector", come in pairs.

SKB IS optical motion sensors are very popular in Russia.

These types of sensors have both a light source and a photodetector. They are located right in the body of these sensors. Each type of sensor is a complete design and is used in a number of machines where increased processing accuracy is needed, up to 1 micrometer. Basically, these are machines with a system H logical P software At board ( CNC) that work according to the program and require minimal human intervention. These non-contact sensors are built on this principle

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

Pros:

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

Minuses:

• at large sensing distances, fine adjustment of the photodetector to the optical beam is required.

Reflex

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

The principle of operation can be seen in the figure below.

Light from the emitter is reflected from some 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 - diffusion - denoted by the letter D. They may look different:

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

Capacitive and inductive sensors

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

They are very similar to each other. The principle of their operation is associated with a change in the magnetic and electric fields. Inductive sensors are triggered when any metal is brought to them. They do not “peck” on other materials. Capacitive ones work on almost any substance.

How an inductive sensor works

As they say, it's better to see once than 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

WBI sensor brand blah blah blah blah, S - sensing distance, here it is 2 mm, U1 - version for a temperate climate, 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 up to 200 milliamps of current to the load, I think this is decent.

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

Well, let's evaluate the work of the sensor? To do this, we cling to the load. The load we will have is an LED connected in series with a resistor with a nominal value of 1 kOhm. Why do we need a resistor? The LED at the moment of inclusion begins to frantically eat current and burns out. To prevent this, a resistor is placed in series with the LED.

On the brown wire of the sensor we supply a plus from the Power supply, and on the blue wire - a minus. The voltage I took was 15 volts.

The moment of truth is coming ... We bring a metal object to the working area of ​​​​the sensor, and the sensor immediately works, as the LED built into the sensor tells us, 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, the sensor, when triggered, outputs a logic one signal that can be used in digital devices.

Conclusion

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

Buy 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 a variety of inductive sensors.