What is the purpose of the sensors. Proximity sensors: overview, principle of operation, purpose

A modern car is made up of many mechanical, electromechanical and electronic components. Optimal operation of the engine must be ensured regardless of external conditions. When external factors change, the operation of nodes and components must adapt to them. Vehicle sensors serve as a kind of tracking device for the operation of the car. Consider the main sensors:

3. Air flow sensor in a car - what does it affect?

The principle of operation of the air flow sensor is based on measuring the amount of heat given off to the air flow in the engine intake manifold. Heating
the sensor element is installed in front of the car's air filter. Change
air flow rate and, accordingly, its mass fraction, is reflected in the degree
changes in the temperature of the heating coil of the MAF sensor.

"Tripling" of the engine during operation and loss of power indicates a possible failure of the air flow sensor.

4. Oxygen sensor, lambda probe - sensor malfunction

An oxygen sensor or lambda probe detects the amount of oxygen left in the exhaust manifold after fuel combustion. The lambda probe is part of the electronic engine management system, which regulates the amount of fuel, ensuring its complete combustion. Increased fuel consumption characterizes a possible sensor malfunction.

5. Throttle sensor - symptoms of malfunction

This sensor is an electromechanical device consisting of a sensing element and a stepper motor.

The sensitive element is
temperature sensor, and the stepper motor is the actuator.
This electromechanical device changes the position of the throttle valve
relative to the coolant temperature. Thus, the rotation frequency
crankshaft of the engine depends on the degree of heating of the coolant.

A characteristic symptom of a malfunction of this sensor is the lack of warm-up speed and increased fuel consumption.

6. Oil pressure sensor - functions, failure

On cars of the Japanese brand, a diaphragm oil pressure sensor is installed
type. The sensor consists of two cavities separated by a flexible membrane. Butter
acts on the membrane on one side, bending from pressure. In the measuring
The membrane of the sensor cavity is connected to the rheostat rod.

Depending on the engine oil pressure, the diaphragm flexes more or less, changing the overall resistance of the sensor. The oil pressure sensor is located on the engine block.

A burning oil pressure light on the car panel may indicate a sensor failure.

7. Is the knock sensor in the engine not working?

The engine knock sensor measures the ignition timing. During normal engine operation, the sensor is in "idle" mode. When the process changes
combustion in the direction of the explosive nature of the combustion of fuel-detonation, the sensor sends a signal electronic system engine control to change the advance angle
ignition in the direction of decreasing.

It is located in the air filter area on the cylinder block. To check the performance of the knock sensor, you must run.

8. Camshaft angle sensor - troit engine

This sensor is located on the cylinder head and measures the engine speed.
camshaft of the engine, and based on the signals from the sensor, the control unit determines the current position of the pistons in the cylinders.

Uneven engine operation and tripling indicate incorrect operation of the sensor. The check is carried out using an ohmmeter, measuring the resistance between the sensor terminals.

9. ABS / ABS sensor in the car - check the performance

Electromagnetic type ABS sensors are installed on the wheels of the car and are part of the car's anti-lock braking system.

Sensor function is the measurement of wheel speed. The object of measurement of the sensor is the signal gear disk, which is mounted on the wheel hub. If the ABS sensor is faulty, the control light on the control panel does not go out after starting the engine.

The technology for determining the operability of the sensor is to measure the resistance between the contacts of the sensor, in case of a malfunction, the resistance is zero.

10. Fuel level sensor in a car - how to check if it works?

The fuel level sensor is installed in the fuel pump housing and consists of several components. The float, through a long rod, acts on a sector rheostat, which changes the resistance of the sensor depending on the fuel level in the car's tank. The sensor signals are sent to a pointer or electronic pointer on the vehicle control panel. Checking the performance of the fuel level sensor is carried out with an ohmmeter, which measures the resistance between the sensor contacts.

What is a sensor?

Surely you have heard the word “sensor” more than once. Obviously, this word means some kind of technical device. What is a sensor and how does it work? What types of sensors are there? Let's consider all these questions in more detail.

The concept of a sensor

Currently, it is common to call a sensor an element that converts information received from the medium into an electrical signal in order to further transfer information to some other device. Typically, the sensor is a structurally separate part of the measuring system.

Sensors are used everywhere: in cars, heating systems, water supply, in production, in medicine, even in catering establishments to measure temperature in order to determine the degree of readiness of a dish.

Sensor classification

There are several types of sensor classification. We present the most basic ones.

By type of measurement:

• Pressure Sensors;
• Flow sensors;
• Level measurement sensors;
• Temperature measurement sensors;
• Concentration sensors;
• Radioactivity sensors;
• Movement sensors;
• Angular position sensors;
• Sensors for measuring mechanical quantities;
• Vibration sensors.

Classification by manufacturing technology:

• Elemental sensors;
• The sensors are integral.

Classification according to the principle of action:

This includes:

• Optical sensors that use electromagnetic radiation and react to water vapour, smoke and different kinds aerosols. They are non-contact sensors. The principle of their work is based on capturing by a sensitive sensor the impact of any irritant, for example, water vapor. These sensors are widely used in automated control systems.
• inductive sensors. They belong to non-contact sensors, designed to calculate the position of an object. Inductive sensors perfectly capture the fluctuations of the electromagnetic field. Their design is based on a generator, which creates an electromagnetic field, the impact of which on a metal object generates oscillation amplitudes, to which the sensor reacts. Such sensors are widely used in metal detectors, as well as in various kinds of electronic locks.
• capacitive sensors. It is these sensors that are used in cars as rain sensors, touch buttons household appliances, fluid measurement sensors. The principle of their action is to respond to the action of the liquid. The insulator of such sensors has a dielectric constant. The liquid, acting on the insulator, causes the appearance of an electrical signal, which is converted into information. Such sensors are widely used in household appliances.
• Load cells. Load cells are a device for measuring force, pressure, torque, acceleration or displacement. The mechanism of their action is based on the principle of elastic force. Such sensors are widely used in various types of scales. They convert the amount of deformation into an electrical signal, in other words, the sensor detects the impact of some force on it, after which the elastic element is deformed and the resistance of the strain gauge, which is built into such a sensor, changes. Next, the information is converted into an electrical signal and transferred to another device, such as a display.
• Piezoelectric sensors. Such sensors are widely used in microphones and sonars. Their principle of operation is based on the polarization of the dielectric under the influence of mechanical stresses. In other words, piezoelectric sensors pick up a change in the electric field that has been mechanically affected. For example, in a microphone, this is the effect of voice. The result of the deformation will be the conversion of the received signal into an electrical one and its transmission to another device. These sensors were born thanks to Jacques and Pierre Curie in 1880.
• Magnetic-electric sensors. These are sensors whose operating principle is based on the so-called Hall effect. These sensors are used in smartphones as the basis for the operation of an electronic compass, in electric motors, and in current meters.
• Nano sensors. Are under development. The most demanded sphere for them should be medicine and robotics. It is assumed that these sensors will become a new class and will find widespread use in the future. Their principle of operation will be similar to many other sensors (hence the names nano-piezo sensors, nano-strain sensors, etc.), but their dimensions will be many times smaller

To learn more about sensors, read these articles.

Electrotechnical encyclopedia #16.

Sensors

Classification of sensors, basic requirements for them

Automation of various technological processes, effective control of various units, machines, mechanisms require numerous measurements of various physical quantities.

Sensors(in the literature often also called measuring transducers), or in other words, sensors are elements of many automation systems - with their help they receive information about the parameters of the controlled system or device.

Sensor - this is an element of a measuring, signaling, regulating or control device that converts a controlled value (temperature, pressure, frequency, luminous intensity, electrical voltage, current, etc.) into a signal convenient for measurement, transmission, storage, processing, registration, and sometimes to influence them on controlled processes. Or easier sensor is a device that converts the input action of any physical quantity into a signal that is convenient for further use.

The sensors used are very diverse and can be classified according to different criteria:

Depending on the type of input (measured) quantity distinguish between: sensors of mechanical displacements (linear and angular), pneumatic, electrical, flow meters, sensors of speed, acceleration, force, temperature, pressure, etc.

Currently, there is approximately the following distribution of the proportion of measurements of various physical quantities in industry: temperature - 50%, flow (mass and volume) - 15%, pressure - 10%, level - 5%, quantity (mass, volume) - 5%, time - 4%, electrical and magnetic quantities - less than 4%.

By the type of output value to which the input value is converted , distinguish non-electric And electrical: DC current sensors (emf or voltage), amplitude sensors alternating current(EMF or voltage), AC frequency sensors (EMF or voltage), resistance sensors (active, inductive or capacitive), etc.

Most sensors are electrical. This is due to the following advantages of electrical measurements:

It is convenient to transmit electrical quantities over a distance, and the transmission is carried out at high speed;

Electrical quantities are universal in the sense that any other quantities can be converted to electrical quantities and vice versa;

They are accurately converted into a digital code and allow you to achieve high precision, sensitivity and speed of measuring instruments.

According to the principle of action Sensors can be divided into two classes: generating And parametric(sensors-modulators). Generator sensors carry out direct conversion of the input value into an electrical signal.

Parametric sensors convert the input value into a change in some electrical parameter ( R , L or C ) of the sensor.

According to the principle of action sensors can also be divided into ohmic, rheostatic, photoelectric (opto-electronic), inductive, capacitive, etc.

There are three classes of sensors:

Analog sensors, i.e. sensors that produce an analog signal in proportion to the change in the input value;

Digital sensors generating a pulse train or a binary word;

Binary (binary) sensors that generate a signal of only two levels: "on / off" (in other words, 0 or 1); are widely used due to their simplicity.

Requirements for sensors :

Unambiguous dependence of the output value on the input;

Stability of characteristics over time;

High sensitivity;

Small size and weight;

Lack of feedback on the controlled process and on the controlled parameter;

Work under various operating conditions;

- various options installation.

Parametric sensors (sensor modulators) input value X is converted into a change in some electrical parameter ( R , L or C ) sensor. It is impossible to transmit a change in the listed parameters of the sensor without an energy-carrying signal (voltage or current) to a distance. It is only possible to detect a change in the corresponding parameter of the sensor by the reaction of the sensor to current or voltage, since the listed parameters characterize this reaction. Therefore, parametric sensors require the use of special measuring circuits powered by direct or alternating current.

Ohmic (resistive) sensors - the principle of operation is based on a change in their active resistance with a change in length l, cross-sectional area Sor resistivity p:

R= pl /S

In addition, the dependence of the value of active resistance on the contact pressure and illumination of photocells is used. In accordance with this, ohmic sensors are divided into: contact, potentiometric (rheostatic), strain-resistive, thermistor, photoresistor.

Contact sensors - this simplest form resistor sensors that convert the movement of the primary element into an abrupt change in the resistance of the electrical circuit. With the help of contact sensors, they measure and control forces, displacements, temperature, sizes of objects, control their shape, etc. Contact sensors include travel And Limit switches, contact thermometers and the so-called electrode sensors, used primarily to measure the limit levels of electrically conductive liquids.

Contact sensors can operate on both direct and alternating current. Depending on the measurement limits, contact sensors can be single-limit and multi-limit. The latter are used to measure quantities that vary significantly, while parts of the resistor R, included in the electrical circuit, are shorted in series.

The disadvantage of contact sensors is the difficulty of continuous monitoring and the limited service life of the contact system. But due to the extreme simplicity of these sensors, they are widely used in automation systems.

Rheostatic sensors are a variable resistance resistor. The input value of the sensor is the movement of the contact, and the output value is the change in its resistance. The moving contact is mechanically connected to the object whose displacement (angular or linear) is to be transformed.

The most widespread is the potentiometric circuit for switching on a rheostat sensor, in which the rheostat is switched on according to the voltage divider circuit. Recall that a voltage divider is an electrical device for dividing direct or alternating voltage into parts; a voltage divider allows you to remove (use) only part of the available voltage through the elements of an electrical circuit consisting of resistors, capacitors or inductors. A variable resistor connected according to the voltage divider circuit is called a potentiometer.

Typically, rheostat sensors are used in mechanical measuring instruments to convert their readings into electrical quantities (current or voltage), for example, in float level meters for liquids, various pressure gauges, etc.

The sensor in the form of a simple rheostat is almost never used due to the significant non-linearity of its static characteristic. I n \u003d f (x), where I n- load current.

The output value of such a sensor is the voltage drop U out between the moving and one of the fixed contacts. Dependence of the output voltage on the displacement x of the contact U out \u003d f(x) corresponds to the law of change in resistance along the potentiometer. The law of distribution of resistance along the length of the potentiometer, determined by its design, can be linear or non-linear.

Potentiometric sensors, which are structurally variable resistors, are made of various materials - winding wire, metal films, semiconductors, etc.

Strain gauges (strain gauges) are used to measure mechanical stresses, small deformations, vibration. The action of strain gauges is based on the tensoreffect, which consists in changing the active resistance of conductor and semiconductor materials under the influence of forces applied to them.

Thermometric sensors (thermistors) - resistance depends on temperature. Thermistors as sensors are used in two ways:

1) The temperature of the thermistor is determined by the environment; the current passing through the thermistor is so small that it does not heat up the thermistor. Under this condition, the thermistor is used as a temperature sensor and is often referred to as a "resistance thermometer".

2) The temperature of the thermistor is determined by the degree of heating by constant current and cooling conditions. In this case, the steady temperature is determined by the heat transfer conditions of the thermistor surface (the speed of the environment - gas or liquid - relative to the thermistor, its density, viscosity and temperature), so the thermistor can be used as a sensor for flow velocity, ambient thermal conductivity, gas density, etc. In sensors of this kind, a two-stage transformation occurs, as it were: the measured value is first converted into a change in the temperature of the thermistor, which is then converted into a change in resistance.

Thermistors are made from both pure metals and semiconductors.The material from which such sensors are made must have a high temperature coefficient of resistance, if possible a linear dependence of resistance on temperature, good reproducibility of properties and inertness to environmental influences. To the greatest extent, platinum satisfies all these properties; in a slightly smaller one - copper and nickel.

Compared to metal thermistors, semiconductor thermistors (thermistors) have a higher sensitivity.

Inductive sensors serve for contactless obtaining of information about the movements of the working bodies of machines, mechanisms, robots, etc. and converting this information into an electrical signal.

The principle of operation of an inductive sensor is based on a change in the inductance of the winding on the magnetic circuit, depending on the position of the individual elements of the magnetic circuit (armature, core, etc.). In such sensors, linear or angular movement X(input quantity) is converted into a change in inductance ( L) sensor. They are used to measure angular and linear displacements, deformations, dimensional control, etc.

In the simplest case, an inductive sensor is an inductor with a magnetic circuit, the moving element of which (armature) moves under the action of the measured value.

The inductive sensor recognizes and responds accordingly to all conductive objects. The inductive sensor is non-contact, does not require mechanical action, it works non-contact by changing the electromagnetic field.

Advantages

- no mechanical wear, no contact failures

- no contact bounce and false positives

- high switching frequency up to 3000 Hz

- resistant to mechanical stress

disadvantages - relatively low sensitivity, dependence of the inductive resistance on the frequency of the supply voltage, a significant feedback effect of the sensor on the measured value (due to the attraction of the armature to the core).

Capacitive sensors - the principle of operation is based on the dependence of the electrical capacitance of the capacitor on the dimensions, the relative position of its plates and on the dielectric constant of the medium between them.

For a two-plate flat capacitor, the electric capacitance is determined by the expression:

C \u003d e 0 e S /h

where e 0- dielectric constant; e- relative permittivity of the medium between the plates; S- active area of ​​the plates; his the distance between the capacitor plates.

Dependencies C(S) And C(h) is used to convert mechanical movements into a change in capacitance.

Capacitive sensors, as well as inductive ones, are powered by alternating voltage (usually increased frequency - up to tens of megahertz). As measuring circuits, bridge circuits and circuits using resonant circuits are usually used. In the latter case, as a rule, the dependence of the generator oscillation frequency on the capacitance of the resonant circuit is used, i.e. the sensor has a frequency output.

The advantages of capacitive sensors are simplicity, high sensitivity and low inertia. Disadvantages - the influence of external electric fields, the relative complexity of measuring devices.

Capacitive sensors are used to measure angular displacements, very small linear displacements, vibrations, movement speeds, etc., as well as to reproduce specified functions (harmonic, sawtooth, rectangular, etc.).

Capacitive transducers, permittivitye which changes due to movement, deformation or change in the composition of the dielectric, are used as level sensors for non-conductive liquids, bulk and powder materials, the thickness of a layer of non-conductive materials (thickness gauges), as well as monitoring humidity and substance composition.

Sensors - Generators

Generator sensors carry out direct conversion of the input value X into an electrical signal. Such sensors convert the energy of the source of the input (measured) quantity immediately into an electrical signal, i.e. they are, as it were, generators of electricity (hence the name of such sensors - they generate an electrical signal).

Additional power sources for the operation of such sensors are fundamentally not required (nevertheless, additional power may be required to amplify the output signal of the sensor, convert it into other types of signals, and for other purposes). Generators are thermoelectric, piezoelectric, induction, photoelectric and many other types of sensors.

Inductive sensors the measured non-electric quantity is converted into the EMF of induction. The principle of operation of sensors is based on the law of electromagnetic induction. These sensors include tachogenerators of direct and alternating current, which are small electric machine generators, in which the output voltage is proportional to the angular speed of rotation of the generator shaft. Tachogenerators are used as angular velocity sensors.

The tachogenerator is an electric machine operating in generator mode. In this case, the generated EMF is proportional to the rotation speed and the magnitude of the magnetic flux. In addition, with a change in the speed of rotation, the frequency of the EMF also changes. They are used as speed sensors (speed).

temperature sensor And. In modern industrial production, temperature measurements are the most common (for example, in a medium-sized nuclear power plant there are about 1500 points where such measurements are made, and in a large chemical industry there are more than 20 thousand such points). A wide range of measured temperatures, a variety of conditions for the use of measuring instruments and requirements for them determine the variety of temperature measuring instruments used.

If we consider temperature sensors for industrial applications, we can distinguish their main classes: silicon temperature sensors, bimetallic sensors, liquid and gas thermometers, temperature indicators, thermistors, thermocouples, resistance temperature converters, infrared sensors.

Silicon temperature sensors use the dependence of the resistance of semiconductor silicon on temperature. The range of measured temperatures is -50…+150 0 C . They are mainly used to measure the temperature inside electronic devices.

Bimetal sensor made of two dissimilar metal plates fastened together. Different metals have different thermal expansion coefficients. If the metals connected to the plate are heated or cooled, then it will bend, while closing (opening) the electrical contacts or moving the indicator arrow. Operating range of bimetallic sensors -40…+550 0 C. Used to measure the surface of solids and the temperature of liquids. The main areas of application are the automotive industry, heating and water heating systems.

Thermal indicators - These are special substances that change their color under the influence of temperature. The color change may be reversible or irreversible. They are produced in the form of films.

Resistance thermal converters

The principle of operation of resistance thermocouples (thermistors) is based on the change in the electrical resistance of conductors and semiconductors depending on temperature (discussed earlier).

Platinum thermistors are designed to measure temperatures in the range from -260 to 1100 0 C. Cheaper copper thermistors, which have a linear dependence of resistance on temperature, are widely used in practice.

The disadvantage of copper is its low resistivity and easy oxidation at high temperatures, as a result of which the final limit of the use of copper resistance thermometers is limited to a temperature of 180 0 C. In terms of stability and reproducibility of characteristics, copper thermistors are inferior to platinum ones. Nickel is used in inexpensive sensors for measurements in the room temperature range.

Semiconductor thermistors (thermistors) have a negative or positive temperature coefficient of resistance, the value of which at 20 0 C is (2 ... 8) * 10 -2 (0 C) -1, i.e. an order of magnitude greater than that of copper and platinum. Semiconductor thermistors with very small sizes have high resistance values ​​(up to 1 MΩ). as a semi-conductor. The material used is metal oxides: semiconductor thermistors of the KMT types - a mixture of oxides of cobalt and manganese and MMT - copper and manganese.

Semiconductor temperature sensors have a high stability of characteristics over time and are used to change temperatures in the range from -100 to 200 0 С.

Thermoelectric converters (thermocouples) - p The principle of operation of thermocouples is based on the thermoelectric effect, which consists in the fact that in the presence of a temperature difference between the junctions (junctions) of two dissimilar metals or semiconductors, an electromotive force arises in the circuit, called thermoelectromotive force (abbreviated as thermo-EMF). In a certain temperature range, we can assume that thermo-EMF is directly proportional to the temperature difference∆T\u003d T 1 - T 0 between the junction and the ends of the thermocouple.

The interconnected ends of the thermocouple, immersed in the medium whose temperature is measured, is called the working end of the thermocouple. Ends that are exposed to the environment and are usually connected by wires to the measuring circuit are called free ends. The temperature of these ends must be kept constant. Under this condition, thermo-EMF E t will depend only on temperature T1working end.

U out \u003d E t \u003d C ( T 1 - T 0) ,

where C is a coefficient depending on the material of the thermocouple conductors.

The EMF created by thermocouples is relatively small: it does not exceed 8 mV for every 100 0 C and usually does not exceed 70 mV in absolute value. Thermocouples allow you to measure temperature in the range from -200 to 2200 0 С.

Platinum, platinum-rhodium, chromel, and alumel are most widely used for the manufacture of thermoelectric converters.

Thermocouples have the following Benefits: ease of manufacture and reliability in operation, low cost, lack ofpower supplies and the ability to measure over a wide temperature range.

Along with this, thermocouples are also characterized by some limitations- lower measurement accuracy than thermistors, the presence of significant thermal inertia, the need to introduce a correction for the temperature of the free ends and the need to use special connecting wires.

Infrared sensors (pyrometers) - use the radiation energy of heated bodies, which allows you to measure the surface temperature at a distance. Pyrometers are divided into radiation, brightness and color.

Radiation pyrometers are used to measure temperatures from 20 to 2500 0 C, and the device measures the integral radiation intensity of a real object.

Brightness (optical) pyrometers are used to measure temperatures from 500 to 4000 0 C. They are based on a comparison in a narrow part of the spectrum of the brightness of the object under study with the brightness of an exemplary emitter (photometric lamp).

Color pyrometers are based on measuring the ratio of radiation intensities at two wavelengths, usually chosen in the red or blue part of the spectrum; they are used to measure temperatures in the range of 800 0 C.

Pyrometers allow you to measure the temperature in hard-to-reach places and the temperature of moving objects, high temperatures where other sensors no longer work.

To measure temperatures from -80 to 250 0 C, so-called quartz thermal converters are often used, using the dependence of the natural frequency of a quartz element on temperature. The operation of these sensors is based on the fact that the dependence of the transducer frequency on temperature and the linearity of the conversion function change depending on the orientation of the cut relative to the axes of the quartz crystal. These sensors are widely used in digital thermometers.

Piezoelectric sensors

The action of piezoelectric sensors is based on the use of the piezoelectric effect (piezoelectric effect), which consists in the fact that when some crystals are compressed or stretched, an electric charge appears on their faces, the magnitude of which is proportional to the acting force.

The piezoelectric effect is reversible, i.e., the applied voltage causes deformation of the piezoelectric sample - its compression or stretching, according to the sign of the applied voltage. This phenomenon, called the inverse piezoelectric effect, is used to excite and receive acoustic vibrations of sonic and ultrasonic frequencies.

Used to measure forces, pressure, vibration, etc.

Optical (photoelectric) sensors

Distinguish analog And discrete optical sensors. For analog sensors, the output signal changes in proportion to the ambient light. The main area of ​​application is automated lighting control systems.

Discrete-type sensors change the output state to the opposite when the set value of illumination is reached.

Photoelectric sensors can be applied in almost all industries. Discrete action sensors are used as a kind of proximity switches for counting, detection, positioning and other tasks on any technological line.

, registers a change luminous flux in the controlled area , associated with a change in the position in space of any moving parts of mechanisms and machines, the absence or presence of objects. Thanks to the large sensing distances optical proximity sensors found wide application in industry and beyond.

Optical proximity sensor consists of two functional units, receiver and emitter. These nodes can be made both in the same housing and in different housings.

According to the object detection method, photoelectric sensors are divided into 4 groups:

1) beam crossing- in this method, the transmitter and receiver are separated into different housings, which allows them to be installed opposite each other at a working distance. The principle of operation is based on the fact that the transmitter constantly sends a light beam, which is received by the receiver. If the light signal of the sensor stops, as a result of overlapping by a third-party object, the receiver immediately reacts by changing the state of the output.

2) reflection from the reflector- in this method, the receiver and transmitter of the sensor are in the same housing. A reflector (reflector) is installed opposite the sensor. Reflector sensors are designed in such a way that, thanks to a polarizing filter, they perceive reflection only from the reflector. These are reflectors that work on the principle of double reflection. The choice of a suitable reflector is determined by the required distance and mounting possibilities.

The light signal sent by the transmitter is reflected from the reflector and enters the sensor receiver. If the light signal stops, the receiver immediately responds by changing the state of the output.

3) reflection from the object- in this method, the receiver and transmitter of the sensor are in the same housing. During the working state of the sensor, all objects that fall into its working area become a kind of reflectors. As soon as the light beam reflected from the object hits the sensor receiver, it immediately reacts by changing the output state.

4) fixed object reflection - the principle of operation of the sensor is the same as that of "reflection from the object" but more sensitive to deviations from the adjustment to the object. For example, it is possible to detect a swollen cork on a kefir bottle, incomplete filling of a vacuum package with products, etc.

According to their purpose, photo sensors are divided into two main groups: sensors for general use and special sensors. Special sensors include types of sensors designed to solve a narrower range of tasks. For example, detection of a color mark on an object, detection of a contrasting border, the presence of a label on a transparent package, etc.

The task of the sensor is to detect an object at a distance. This distance varies between 0.3mm-50m, depending on the selected sensor type and detection method.

Microwave sensors

The push-button-relay consoles are being replaced by microprocessor automatic systems management technological process(APCS) of the highest performance and reliability, the sensors are equipped with digital communication interfaces, but this does not always lead to an increase in the overall reliability of the system and the reliability of its operation. The reason is that the very principles of operation of most known types of sensors impose severe restrictions on the conditions under which they can be used.

For example, non-contact (capacitive and inductive), as well as tachogenerator speed control devices (UKS) are widely used to monitor the speed of industrial mechanisms. Tachogenerator UKS have a mechanical connection with a moving object, and the sensitivity zone of non-contact devices does not exceed a few centimeters.

All this not only creates inconvenience during the installation of sensors, but also significantly complicates the use of these devices in conditions of dust that sticks to work surfaces, causing false alarms. The listed types of sensors are not capable of directly controlling an object (for example, a conveyor belt) - they are tuned to the movement of rollers, impellers, tension drums, etc. The output signals of some devices are so weak that they are below the level of industrial interference from the operation of powerful electrical machines.

Similar difficulties arise when using traditional level detectors - sensors for the presence of a bulk product. Such devices are necessary to timely shut off the supply of raw materials to production tanks. False alarms are caused not only by sticking and dust, but also by touching the product flow when it enters the hopper. In unheated rooms, the operation of the sensors is affected by the ambient temperature. False alarms cause frequent stops and starts of loaded process equipment - the main cause of its accidents, lead to blockages, breakage of conveyors, fire and explosion hazards.

These problems several years ago led to the development of fundamentally new types of devices - radar sensors for speed control, motion and backwater sensors, the operation of which is based on the interaction of a controlled object with a radio signal with a frequency of about 10 10 Hz.

The use of microwave methods for monitoring the state of technological equipment makes it possible to completely get rid of the shortcomings of traditional types of sensors.

The salient features of these devices are:

Lack of mechanical and electrical contact with the object (environment), the distance from the sensor to the object can be several meters;

Direct control of the object (conveyor belt, chain) and not their drives, tension drums, etc.;

Low power consumption;

Insensitivity to product sticking due to long working distances;

High noise immunity and directivity of action;

One-time adjustment for the entire service life;

High reliability, safety, absence of ionizing radiation.

The principle of operation of the sensor is based on a change in the frequency of the radio signal reflected from a moving object. This phenomenon ( "Doppler effect") is widely used in radar systems for remote speed measurement. A moving object causes an electrical signal to appear at the output of the microwave transceiver module.

Since the signal level depends on the properties of the reflecting object, motion sensors can be used to signal an open circuit (belt), the presence of any objects or materials on the conveyor belt. The tape has a smooth surface and low reflectivity. When the product begins to move past the sensor installed above the working branch of the conveyor, increasing the reflection coefficient, the device signals the movement, that is, in fact, that the belt is not empty. By the duration of the output pulse, one can judge the size of the objects being moved at a considerable distance, make selection, etc.

If it is necessary to fill any container (from the bunker to the shaft), it is possible to accurately determine the moment when filling is completed - a sensor lowered to a certain depth will show the movement of the filler until it is filled.

Specific examples of the use of microwave motion sensors in various industries are determined by its specifics, but in general they are able to solve a wide variety of problems of trouble-free operation of equipment and increase the information content of automated control systems.

List of sources used

1) E.M. Gordin, Yu.Sh. Mitnik, V.A. Tarlyn

Fundamentals of automation and computer science

Moscow "Engineering", 1978

2) Gustav Olsson, Gianguido Piani

Digital automation and control systems

St. Petersburg: Nevsky Dialect, 2001

3) V.V. Sazonov Guidelines for laboratory work

"Research of a rheostatic linear displacement sensor"

4) Chugainov N.G. Abstract "Temperature sensor", Krasnoyarsk 2003

5) Fedosov A. V. Abstract "Speed ​​sensors" - Moscow 2003

6) D. N. Shestakov, Director General of PromRadar LLC

Microwave sensors for industrial applications

7) Journal "Modern Electronics" 6, 2006

8) Catalog of the enterprise "Sensor"

9) OMRON Components / Photoelectric Sensors

Article author : Sergey Nikulin, lecturer, EE "Gomel State Polytechnic college " .

Presence sensor - an electronic device that registers objects of a certain class on the territory of its control by non-contact methods.

Depending on the results of registration, it can switch electrical impulses, on the signals of which other devices perform various kinds of actions.

Automatic switching on of the electric dryer when hands are raised, operation of some types car alarms, stop of conveyors in case of filling of bunkers on industrial enterprises– examples of functioning of presence sensors.

According to the principle of action:

1. ultrasonic: barrier, diffusion;
2. photoelectric: barrier (type B), reflector (type R), diffusion (type D);
3. capacitive;
4. acoustic;
5. infrared;
6. load sensors;
7. combined.

By the number of sensor blocks:

1. single position;
2. on-off;
3. multiposition.

According to the installation method: overhead and embedded.

By the method of receiving the incoming signal: active and passive.

According to the method of transmitting the outgoing signal: wired and wireless.

Let us consider in detail each of the types, determine the areas of their application, evaluate the advantages and disadvantages.

Ultrasonic presence sensors

They emit and receive waves that are not picked up by the human ear (with a frequency of about 200 kHz).

Two modes of operation are possible:

barrier : an ultrasonic wave passes between the sensors located opposite each other. It will not enter the receiver if a foreign object (barrier) appears in the coverage area.

diffusion : Using a sensor that emits a wave and then picks it up as it bounces off an object in the path of the beam.

In both cases, when a foreign object appears, a signal is switched that is transmitted to the executing devices.

Advantages of ultrasonic sensors in comparison with optical sensors performing similar tasks:

• detection of transparent objects;
• immunity to light flashes and glare;
• performance in difficult conditions (fog, dust, steam).

Disadvantages:

• low range (upper threshold) fixation;
• unreliability of registration of objects made of soft materials (fabric, porous rubber);
• the presence of a “blind zone” (lower detection threshold).

Examples of the use of ultrasonic sensors: parking systems of modern cars, counting the number of units of finished products on the conveyor.

Photoelectric presence sensors

Photoelectric sensors B and D type work in a similar way to ultrasonic circuit. The difference lies in the use of optical radiation instead of ultrasonic radiation. This provides the following benefits:

• high fixation threshold (up to 150 meters for barrier sensors);
• speed;
• no blind zone.

Disadvantages:

• inability to register transparent objects;
• failures in fog, dust, light flashes and glare.

For type P sensors, the receiver and emitter are mounted in one housing. The emitted beam is reflected from a reflector (reflector, reflector) located at a distance of up to 8 meters, and returns back. The device gives a signal if the luminous flux is interrupted by the control object.

Compared to type B, type P loses its range, but its advantages are compactness and ease of installation.

Photoelectric sensors are used to control packaging and production lines, check the filling level of transparent containers, prevent unauthorized access to closed areas, stop industrial equipment when a person enters the danger zone.

capacitive

Structurally, they are cylindrical or plane-parallel capacitors.

When an object appears in the coverage area, their dielectric constant changes, and hence the capacitance, which causes a trigger (see).

Devices are used to control the filling of tanks with liquids and bulk materials, as counters of units of finished products and elements of car anti-theft systems.

The advantages of capacitive sensors are low inertia and high sensitivity threshold. The disadvantage is the likelihood of malfunctions under the influence of external electromagnetic fields.

Acoustic presence sensors

In them, by means of piezoelectric materials, a sound wave is converted into an electrical signal.

They are microphones operating in the frequency range of 20-20000 Hz:

• low-resistance (inductors with moving magnets);
• high-resistance (equivalent variable capacitors).

They are used as sound light sensors that work in conjunction with and save energy. When the noise threshold in the room is exceeded, automatic switch on Sveta. If there is silence, after 20-25 seconds the lamps turn off.

Advantages of the device:

• simplicity of design;
• reliability.

Disadvantages:

• the need to use amplifiers;
• the probability of false alarms as a result of external and internal noise (sharp sounds from the street, turning on the radio, phone calls).

Infrared presence sensors

The principle of operation of devices is based on fixing changes in the flow of infrared (IR) rays as a result of human movements. His stay is recognized by the greater intensity (in comparison with interior items) of radiation, which directly depends on body temperature.

The main parts of the sensor are photocells and a multilens consisting of a large number of segments - small lenses. Each of them directs the rays falling into it to a photocell.

Moving, a person finds himself in the zones of control of different segments. The light on the photocell appears and disappears, generating an electrical signal.

In a strict sense, according to the principle of operation, such a device is, and not presence. The latter category includes particularly precise instruments with a large number of control areas. They are able to detect the presence of a person who is in a state of almost complete rest. The smallest gestures are recorded: shaking the head, pressing the keyboard with fingers, etc.

Detection radius (R) is the main characteristic of the device. Its installation should be carried out in such a way that the distance to the farthest corners of the room does not exceed R. Large rooms require the installation of several sensors.

It is necessary that there are no partitions on the path of the IR beam, even glass ones, which are opaque for it.

It is unacceptable to hit the device with direct light from lamps, it must be at a maximum distance from fans, air conditioners and heaters.

Infrared sensors are used as a means, as an additional and for automation of power supply, leading to cost savings.

Their advantages:

• adjustment accuracy;
• complete safety for health due to the absence of any type of radiation;
• reaction only to objects whose temperature exceeds the threshold.

Disadvantages:

• inaccuracy of functioning in open spaces (influence of precipitation, sunlight);
• the probability of false inclusions under the influence of warm air currents;
• interference from objects that do not transmit infrared radiation;
• low operating temperature range.

Load cells

These are converters that convert mechanical force into electrical current.

Structurally, the sensor is a strain gauge in the form of a thin wire, zigzag like a car glass heater, fixed on an elastic substrate. As an elastic element, fabric, rubber, polymer film are used.

Under the action of force, the conductor is deformed, its resistance changes, which generates an electrical signal that is supplied after amplification to the actuators.

Use of appliances:

Like passenger presence sensors. Regular - for safety purposes (indication of a fastened seat belt and data for the deployment of airbags). Installed individually - to control the operation of a taxi (fixing the state of the car - "free / busy").

As stationary and security elements, signaling unauthorized access to the premises.

The advantage of strain gauge load cells is their low thickness, which provides hidden installation (camouflage under a rug at the door), and ease of installation on passenger seats.

Disadvantages:

• the need to use a signal amplifier;
• susceptibility to repeatedly repeated mechanical loads, which leads to failure;
• decrease in sensitivity to temperature changes.

Combined presence detectors

Sometimes one type of device is not enough to achieve your goals. In such cases, they can be used several with different principles of operation.

Using an example, we will consider the operation of an infrared presence sensor in combination with a light sensor.

The first gives a signal to turn on the lamps when it detects a person in the room.

The second - in the case of light indicators below the set threshold value.

Working together, they will automatically turn on the lamps only if there are people in the room at night.

This approach creates comfortable living conditions and leads to 30-40% energy savings.

When protecting objects, sensors with different operating principles are combined into systems. This improves reliability and reduces the number of false positives.

Presence sensor device

Sensors are devices consisting of one (single-position), two (two-position) or several (multi-position) blocks. Each is a device in a plastic case with a microcircuit for sending, receiving and processing signals.

Their design feature is the absence of moving, mechanically loaded parts. An exception is elastic substrates with strain gauges in load cells.

Consequently, possible faults limited to the failure of microcircuit parts and self-elimination are not subject.

Sensor mounting options. Depending on the design features sensors are installed in mounting boxes or directly on the walls or ceiling (surface models).

None of the methods gives advantages in operation; only design decisions can affect the choice.

Ways to receive a signal. According to the method of receiving a signal, there are two types of presence sensors:

• active - radiate energy in environment and receive data based on the response (ultrasonic, photoelectric);
• passive - fix objects according to their properties, without first sending signals (infrared, acoustic, capacitive, load sensors).

Signal transmission by presence detectors. Having received and processed the information, the presence sensor sends a signal to the actuators:

• through electrical wires;
• over a secure radio channel.

In the second option, the distance between the sensor and the receiving unit reaches 200 m. The use of amplifiers increases this figure, and the obstacles on the way reduce it.

During wireless transmission of a signal for communication with a specific actuator, the sensor is assigned its code. This is done by installing jumpers (jumpers).

If you use devices with a learning code, then there is no need to install jumpers: for switching, it is enough to simultaneously press the special buttons on the sensor and the receiving unit.

The advantages of wireless signal transmission are ease of installation of equipment and reduced costs for electrical wires.

Manufacturers and models of presence sensors

Let's consider what models of presence sensors are offered by global companies.

Theben AG (Germany)

Paul Schwenk founded a company in Stuttgart in 1921 that made timers and watch accessories.

The prudent owner, seeking to save money, invented and in 1930 launched the first countdown sensor for lighting control, which became a bestseller.

The success stimulated a further drive for innovation, which made Theben AG the European leader in the production of efficient energy saving devices, various sensors, "smart" devices, etc.

Theben presence sensors controlling the lighting system:

SPHINX 104-360	SPHINX 104-360/2	SPHINX 104-360AP
Operating principle
infrared	infrared	infrared
Mounting method
ceiling, built-in	ceiling, built-in	ceiling, overhead
Coverage angle
360 about	360 about	360 about
control radius
7 m	7 m	7 m
Number of channels
1	2	1
Max. lamp power
1800 W	1800 W	2000 W
Light level
10-2000 lx	10-2000 lx	10-2000 lx
Turn off delay
1 s-20 min	1 s-20 min	1 s-20 min
Protection level
IP 41	IP 41	IP 41

All devices are equipped with a built-in adjustable light meter and remote control remote control(cm. ).

SPHINX 104-360/2 has a second output channel, with a turn-off delay of 10 seconds - 60 minutes, the signal from which can be sent to the air conditioner, electric heating radiator, fan.

OMRON (Japan)

OMRON company (Kyoto), founded by Kazuma Tateishi in 1933. In the post-war years, it became one of the creators of the "Japanese economic miracle".

The main activity is the production of automation and sensor devices. In this area, it owns more than 40% of the Japanese market. The company's annual turnover is over $5 billion.

OMRON photoelectric detection sensors:

E3FA/E3FB-B/-V	E3H2	E3T-C
Object detection: maximum sensing distance
barrier regime
20 m	15 m	4 m
reflex mode
4 m	3m	2 m
diffuse mode
1m	0.3 m	0.3 m
Light source (wavelength)
red LED (624 nm)	red LED (624 nm)	LEDs: infrared (870 nm), red (630 nm)
Supply voltage
10-30V DC	10-30V DC	10-30V DC

The E3H2 has a bright LED indicator for easy alignment, and the E3T-C's dimensions make it easy to mount in tight spaces.

ESYLUX (Germany)

ESYLUX (Arensburg) develops and manufactures luminaires for emergency and outdoor lighting, presence and motion sensors, smoke detectors, . Confirmation high level products is the quality mark “German Engineering” received by it. Branches and sales offices of the company are open in 13 countries

The table shows examples of presence sensors manufactured by ESYLUX.

PD 360/8 Basic	PD 360/8 Basic SMB	PD 180i/R
Operating principle
infrared	infrared	infrared
Mounting method
ceiling, overhead	ceiling, built-in	wall, built-in
Coverage angle

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:

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

● linear sensors with multi-element linear arrays;

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

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

● two-dimensional grating sensors 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 sectoral mechanical sensors (Fig. 2.11 a, 2.11 b), the working surface (protective cap) closes 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 sectoral mechanical sensors, in addition to the operating frequency, is the angular size of the scanning sector, which is indicated in the sensor marking (sometimes the length of the corresponding arc H of the working surface is additionally given). Marking example: 3.5 MHz/90°.

In linear, convex, microconvex and phased (sector) electronic scanning sensors, the working surface coincides with the radiating surface of the transducer, which is called aperture, and is equal in size to it. Characteristic aperture sizes are used in sensor labeling and help determine when choosing a sensor.

In linear sensors, the aperture length L is characteristic (Fig. 2.11 c), since it determines the width of the rectangular viewing area. An example of marking a linear sensor 7.5 MHz / 42 mm.

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

In convex sensors, the field of view 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 the degree of Fig. 2.11 d. An example of marking a convex sensor: 3.5 MHz / 60 ° / 60 mm. Less often, you use a radius for marking R curvature of the working surface, for example:

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

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

sector mechanical (a - cardiological, b - with water

nozzle); c - linear electronic; d - convex;

e - microconvex; e - phased sector

In microconvex sensors, R is characteristic - the radius of curvature of the working surface (aperture), sometimes the angle of the arc α is additionally given, which determines the angular size of the viewing sector (Fig. 2.11,e). 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 examination. 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 the areas of medical application.

1. Universal sensors for outdoor examination(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). They are 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 associated with the peculiarity of observation through the intercostal gap. Mechanical scanning sensors (single-element or with an annular array) and phased electronic sensors are used.

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

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

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

● Transrectal sensors (transrectal or endorectal probe).

● Intraoperative sensors (intraoperative probe).

● Transurethral sensors (transurethral probes).

● Transesophageal probes.

● Intravascular sensors (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 of narrow application can be singled out, and they should be mentioned separately.

● Ophthalmic sensors (ophtatmology probes).

● Sensors for transcranial studies (transcranial probes).

● Sensors for diagnosing sinusitis, frontal sinusitis and sinusitis.

● Sensors for veterinary medicine (veterinary probes).

8. Broadband and multi-frequency sensors. In modern complex devices, broadband sensors are increasingly used. These sensors are structurally 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 band of operating frequencies.

9. Doppler transducers. Sensors are used only to obtain information about the speed or range of blood flow speeds in the vessels. These transducers are discussed in the sections on Doppler ultrasound instruments.

10. 3D Imaging Sensors. Special sensors for obtaining 3D (three-dimensional) images are rarely used. More commonly, conventional two-dimensional image sensors are used along with special devices that provide scanning along the third coordinate.

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

There are no agreed criteria for evaluating the class of devices among manufacturers and users of ultrasonic 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 estimate the level of complexity of the equipment, on which the quality of the information received largely depends. One of the main technical parameters that determine the level of complexity of an ultrasound scanner is the maximum number of receiving and transmitting channels in the electronic unit of the device, since the greater the number of channels, the better the sensitivity and resolution - the main characteristics of the quality of an ultrasound image.

In simple (usually portable) ultrasound scanners, the number of transmit-receive channels is not more than 16; in devices of the middle and higher class, 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 advanced ultrasound scanners are devices with color Doppler mapping.

High-end appliances usually take full advantage of modern features digital processing signals, starting almost from the output of the sensors. For this reason, such devices are called digital systems or platforms (digital system).

test questions

1. What is acoustic impedance and its effect on reflection

ultrasound?

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

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

4. What modes of operation are provided for in ultrasonic scanners?

5. What is the mode of operation IN?

6. What is the mode of operation BUT?

7. What is the mode of operation M?

8. What is the mode of operation D?

9. Explain the operation of the ultrasonic transducer.

10. What configurations of piezoelectric elements are found in various types

sensors?

11. What types of sensors exist in ultrasound scanners?