Presence sensors. Non-contact sensors: overview, principle of operation, purpose. Touch switch Automatic device sensor what does
- Sensors of the first type are responsible for the diagnosis and performance of the brakes and steering system.
- Second-class devices monitor the condition of the power unit, transmission, suspension and tires.
- The third category of sensors should provide protective functions vehicle and ride comfort.
- Intelligent integrated sensors reduce the load on the control unit. The devices are connected by flexible communication lines; several electronic devices can be used in conjunction at the same time. Such sensors are able to process even low-intensity signals.
- Fiber optic type electronic devices are highly sensitive to dirt and high blood pressure. Because of this, they are short-lived, weakly perceive electromagnetic interference. Such sensors are not suitable for all types of vehicles, because special taps and connectors are required to connect them.
Engine sensors
To optimize the operation of the power unit, as well as monitor the health of components and mechanisms, the following sensors are installed on car engines.- The air sensor is designed to monitor the amount of air entering the intake tract. The flow meter is a reliable device, and moisture is considered its main enemy. If the device fails, the engine runs unstably, the effect of "triple" appears, and increased fuel consumption is observed. The flow meter is built into the intake tract immediately after the air filter.
- "Lambda probe" monitors the mass fraction of oxygen leaving the exhaust manifold. The device doses the fuel supply, starting from the oxygen concentration. The "lambda probe" is located in the exhaust system.
- In the exhaust gas regeneration system of modern cars, electronic devices are installed that control the concentration of nitrogen oxide. They are located in the throttle assembly. As soon as the device is contaminated, the number of repetitions of regeneration cycles will increase.
- The EGR valve sensor is designed to reduce the concentration of harmful gases emitted into the atmosphere. With a sharp acceleration of the car, the device slightly opens the valve, and the exhaust gases are sent to the combustion chambers. Thus, it happens complete combustion hydrocarbons.
- In gasoline engines, a Hall sensor is used. The device is installed in the rear cover of the camshaft and measures its position angle. The received signals from the Hall sensor change the speed of the pistons in the cylinders.
- The throttle sensor takes readings from the accelerator pedal. The device adjusts the operation of the throttle valve based on the temperature of the coolant. The colder the antifreeze, the slower the crankshaft rotates. The sensor is mounted on the throttle pipe and is interconnected with the damper.
- The crankshaft position sensor responds to the timing of fuel delivery by relating the dosage to the injection timing or ignition timing. The device takes readings from the toothed pulley, so it is mounted at the bottom of the cylinder block. Once the sensor fails, the engine cannot be started.
Pressure Sensors
The principle of operation of pressure sensors is approximately the same. But they are installed in a variety of nodes and mechanisms of the car. There are devices of primary and secondary importance. Sensors of paramount importance
Instruments of paramount importance that measure pressure include:- pressure sensor in the intake tract, which provides the relationship between the crankshaft speed (load level) and the flow of the fuel mixture;
- The tire pressure sensor monitors the preset range for the safe driving of vehicles. It is built into the wheel.
Secondary sensors
oil pressure sensor Depending on the vehicle configuration, the number of secondary sensors may vary significantly. - The oil pressure sensor is present in cars of Japanese manufacturers. The membrane type device determines the pressure indicator due to the deflection of the membrane. The sensor is built into the cylinder block.
- The fuel pressure sensor is installed in the fuel pump. At a low rate, the device gives a command to the booster pump.
- The ABS module has a brake fluid pressure sensor.
- Some cars have sensors under the seats that detect the weight of the passenger.
Temperature sensors
Special devices for measuring the temperature of technical fluids and gaseous compounds in a car are found in many systems. - To monitor the temperature of the coolant, a special sensor is installed in the thermostat or cylinder head. He defines temperature regime engine, and when the upper limit is exceeded, it gives a command to turn on the fan. If the coolant warning light comes on in the instrument panel, this indicates a problem with the system.
- For the smooth operation of the engine, it is important to control the temperature of the oil. The sensor is mounted in the oil filter housing.
- Being in the car, it is useful for the driver to know about the temperature of the atmospheric air. temperature sensor environment installed in front of the car.
- Many vehicles equipped with climate control systems are equipped with cabin air temperature sensors. Devices are mounted in a torpedo.
Sensors in the fuel system
To match the quality and quantity of fuel to the load on the engine, a number of sensors are used in the fuel system. - The device that controls the fuel level is mounted in the tank. It is equipped with a float with a long rod and a sensor rheostat. The fuel level indicator directly depends on the resistance value of the sensor.
- There is also a fuel flow sensor in the fuel system. It converts the amount of passed fuel into electrical impulses. Distinctive features instrument are precision and reliability.
- The electronic altimeter device is built into the engine control unit. It regulates the flow of exhaust gases into the combustion chambers depending on atmospheric pressure.
- The correct organization of the operation of the gas distribution mechanism is provided by the phase meter. It is installed near the air filter. When the sensor wears out, the fuel mixture becomes too rich.
- The knock sensor is designed to measure the ignition timing. A meter is installed between the engine cylinders. Upon failure, an increase in detonation is observed due to an increase in the number of explosive processes.
Electrotechnical encyclopedia #16.
Sensors
Classification of sensors, basic requirements for them
Automation of various technological processes, effective management 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 controlling device that converts a controlled value (temperature, pressure, frequency, light intensity, electrical voltage, current, etc.) into a signal that is convenient for measuring, transmitting, storing, processing, recording, and sometimes for influencing 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: sensors direct current(EMF or voltage), AC amplitude sensors (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 make it possible to achieve high accuracy, 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 mounting options.
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 is the simplest type of 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 sensors. 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.
Considering temperature sensors for industrial applications, then their main classes can be distinguished: silicon temperature sensors, bimetallic sensors, liquid and gas thermometers, temperature indicators, thermistors, thermocouples, resistance thermocouples, 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 electrical resistance 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 in the 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 the loaded technological equipment- the main cause of its accidents, lead to blockages, breakage of conveyors, the occurrence of 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 sensors.
Distinctive features these devices are:
The absence of mechanical and electrical contact with an 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), you can accurately determine the moment when filling is completed - the 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 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 to fulfillment 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, CEO OOO "PromRadar"
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 " .More recently, only three sensors could be found in the car, showing the level of pressure and fuel, as well as the temperature of the coolant. At the same time, they did not affect the operation of the engine and automotive systems as a whole, but only informed the driver of the indicated parameters using light or other signals. After the advent of electronic control units, the number of sensors used in the machine has greatly increased, as well as their importance, since it is on their readings that the interaction of the unit with the power unit is based. To ensure the safety and better handling of the vehicle, new devices are constantly being developed to make the use of the car even more comfortable. In this article, we will tell you what automotive sensors exist today, and also talk about the features of their operation.
Device classifications
All existing species automotive sensors, relays and switches are usually divided into several classes:
- The first is devices that control the operation of the brake system and steering. This class also includes sensors responsible for the safety of passengers.
- The second is a device that controls the operation of the transmission, as well as sensors to monitor the operation of the engine, wheels and suspension.
- The third is devices responsible for protecting the car from accidents and other emergency situations.
There is also a separate class of auxiliary equipment, which includes, for example, parking sensors.
The achievements of modern electronics make it possible to make the device more intelligent and remove some of the load from the control unit. In other words, the device itself can determine whether to signal some kind of anomalous behavior or not. In addition, the device can be active or passive. In an active sensor, electrical impulses occur during operation, while a passive sensor simply converts other external energy into electrical energy.
Engine control sensors
These include:
- A device for monitoring the level of oxygen and nitrogen in the fuel. This class also includes sensors that affect the ratio in the fuel-air mixture.
- Devices that determine the speed of rotation and the position of various shafts and elements in the engine.
- Pressure sensors (oils, as well as other liquids or gases). This group also includes a device that measures the level of the above substances.
- temperature sensors.
- A device responsible for the operation of the fuel system and monitoring possible detonations.
Sensors that analyze the state of gases
The car oxygen sensor (lambda probe) is located in the exhaust manifold and allows you to optimally consume gasoline or diesel fuel. The device determines the amount of oxygen remaining after combustion and regulates the amount of air in the chamber. Engine tripping and increased fuel consumption may indicate that the device is out of order and the air in the combustion chamber is rarefied (vacuum effect), which disrupts the operation of the power unit. The sensor is installed in the exhaust manifold near the steering rack.
An apparatus that determines the concentration of nitric oxide in the neutralizer. When it breaks, a constant repetition of regeneration cycles is observed. Mounted on the surface of the throttle assembly.
A sensor that controls the level of air sucked in by the power unit (DTVV). It is located next to the air filter and consists of two platinum filaments heated by electric current. One of them is located in the air channel, so when the air pressure increases, due to the cooling of the thread, its resistance changes. The control unit (ECU), analyzing the voltage difference on both threads, corrects the amount of air in accordance with the norm. Over time, the device becomes dirty, which causes the sensor to become unstable.
Intake air temperature sensor (DTVV)
Important! To clean the thread, do not use any solvents, as well as toothpicks, cotton wool, etc. In this case, you should contact a car service.
In turbo engines, an absolute pressure sensor can be installed, which consists of two cylinders, in one of which the air is pumped out. The difference in pressure between them is the indication.
A sensor that measures the opening of the EGR valve. Allows to reduce the level of toxicity of exhaust gases during excessive warming up of the engine.
Altimeter. Informs the electronic control unit about atmospheric pressure. This allows you to regulate the boost and more competently produce exhaust gas recirculation.
Speed sensors
These are devices that analyze the speed of rotation of the crankshaft. They are partly responsible for the fuel supply and the spark time in the engine. The devices are very hardy, because it is an ordinary magnet with a wire wound around them. If they fail, it is not possible to start the power unit, since the electronic control unit cannot calculate the speed and position of the crankshaft.
If you still managed to start the engine, then it will constantly stall and behave unpredictably at high speeds. The device is located in the lower block with cylinders.
Throttle position sensor. His work is based on the readings read from the gas pedal. It consists of two elements - a stepper motor and a coolant temperature sensor. The stronger the pressure on the gas pedal and the higher the coolant temperature, the faster the crankshaft rotates. As in the previous case, problems with this device lead to interruptions in the operation of the engine.
Automotive hall sensor. Determines the angle of rotation of the camshaft and is responsible for changing the position of the pistons in the cylinders. In the event of malfunctions in its operation, the control unit cannot accurately calculate the time for fuel and spark supply.
Vehicle speed sensor (DSA). It is installed next to the gearbox and reports any changes in the speed of the machine. The device is not particularly reliable.
Camshaft phase sensor. The device is mounted only on an engine with sixteen cylinders and determines the sequence of operation of each of them. Violations in the operation of the device leads to the inclusion of a pair-parallel mode of fuel supply, which automatically affects its consumption. It is installed in the upper part of the block with cylinders.
Idling regulator. The sensor is necessary to stabilize the supply of the fuel-air mixture to the engine, as well as to equalize the speed of the latter when idling. When the throttle is closed, the unit increases or decreases the air flow through the additional channel. IAC allows you to maintain optimal engine speed for its normal warm-up. A malfunction of the device is expressed in the unstable operation of the power unit at idle. The regulator is mounted on the throttle body and secured with four screws. Unfortunately, on some vehicles, the dismantling of this sensor is difficult because the heads of the mounting screws are drilled out and planted on the varnish. It should be noted that such devices are rarely connected to the vehicle's diagnostic system, so the "Check engine" lamp does not light up. Checking the health of the device is based only on the symptoms that appear. However, you can check the engine with a vacuum gauge to find the hero of the occasion.
Sensors showing the level and pressure of liquids
The fuel level sensor (FLS) in the general case is a conventional float connected to a rheostat. When the fuel level drops to a certain value, the contacts close, accompanied by a light signal on the dashboard. The brake fluid level sensor, which is installed next to the anti-lock braking system, works on the same principle.
Oil pressure sensor. It is a chamber divided into two parts by a small membrane. When the oil moves, this membrane flexes, moving the potentiometer, which leads to a change in the resistance of the rheostat built into the device. These changes are monitored by the ECU. The fuel pressure sensor, mounted in the fuel pump, works the same way.
A device that determines fuel consumption. It is usually installed on official vehicles in order to prevent unscrupulous drivers from draining gasoline.
Thermo sensors
These include:
- Air temperature sensor in the car. Mounted on the dashboard and shows the temperature in the cabin.
- A sensor that reports the ambient temperature. Installed next to the grille.
- The coolant temperature sensor (antifreeze), which is responsible for turning the fans on and off, as well as displaying readings on the corresponding display. It is located between the thermostat and the cylinder head. The main malfunctions are a break in the supply wire or a broken contact connection inside the device.
- Engine temperature sensor that informs the ECU about its critical excess. It is an additional security measure.
- Thermal sensor installed in the base of the oil filter. Monitors oil condition to improve engine performance.
Any type of temperature sensor works according to the same principle - when the temperature changes, the resistance between the terminals also changes, which is reflected in the readings of the device. Some of these sensors do not affect the engine in any way, while others, such as the engine coolant temperature (CTO) sensor, are very important. Without their work, the characteristics of the motor are greatly reduced, and in some cases the power unit may even fail.
Such devices are also used in other car systems, for example, for thermal control of the oil level in the box, or in the air conditioner to maintain the optimum temperature.
knock sensor
This device monitors all detonation processes occurring in the engine. It is necessary for uniform fuel consumption. The system is similar to the pickup on a turntable and tracks all sounds at a specific frequency. As a result, the ECU "hears" what is happening with the motor. As soon as the sensor detects a slight knock caused by unevenness between the ignition and fuel injection cycles, the electronic control unit immediately corrects the time between them. When the sensor fails, fuel consumption increases, the engine begins to behave unpredictably (stall, change speed sharply, triple).
Additional sensors for safety
Varieties of this equipment:
- Tire pressure measuring device. As a rule, some of the most expensive tires are equipped with such sensors. The sensor improves driving safety, as it monitors changes in tire pressure in the car and informs the driver about them using light or sound signals.
- abs(). Monitors the speed of rotation of the wheels and does not allow them to completely block during braking in order to prevent the vehicle from skidding. The system can be active or passive. The first option is preferable, since such a device can be controlled by an on-board computer, which increases its efficiency. However, it should be noted that the operation of active automotive sensors requires power from the battery or from the generator.
- Sensors that determine the number of passengers in the cabin. Either the pressure on the seat or the number of seat belts fastened can be analyzed. As a rule, this information is used when calling emergency services by special systems, for example, Era Glonass.
- Vehicle impact sensor. Devices react to the coup of the car, as well as to various collisions. Like sensors to determine the number of passengers, such devices are used to call emergency services.
- Light sensor. It consists of a photosensor that reacts to changes in illumination. At dusk, the light sensor will automatically turn on the parking lights. Using the switches, the device can be turned off to conserve battery power. In addition, it is possible to turn on the headlights directly without using the sensor, since the latter only reacts at night, and the traffic rules imply the use of headlights in the daytime. Nevertheless, for all its advantages, the light sensor has one significant drawback - it can work when you don't need it at all.
- Rain sensor in the car (DDA). It consists of two devices - a photocell and a humidity sensor. Under certain conditions (when the photocell detects the presence of raindrops, and the humidity sensor confirms this), the wipers will turn on automatically. Moreover, the intensity of their work will be determined by the same sensor. When the weather becomes clear again and there is no need to use the wipers, they will automatically turn off.
- Parking sensors. They are a radar that shows the distance to objects when the driver starts to park. The design of the parking sensor can include not only the radar itself, but also a rear-view camera.
Car alarm sensors
In the case of installing a car alarm on a car, the system will be enriched with several more car sensors, relays and switches.
- Vehicle tilt sensor. Controls the position of the body and turns on the alarm if the machine begins to tilt. Also, the sensor reacts to any movement of the machine, for example, made with the help of a tow truck.
- Motion Sensor. It is placed in the cabin and reacts to everything that happens inside. Sometimes it can be equipped with a microphone for more accurate tracking.
- contact sensors. They are installed on the doors, as well as on the trunk and hood. Respond to any hacking attempt.
- A device that measures the level of voltage in the network. Gives an alarm when the current or voltage drops. Allows you to track any attempts to connect or disconnect components from the battery.
- Volume sensor. It reacts to the opening of the door (if for some reason the other sensors did not work or were turned off), as well as to any change in the volume of air that occurs, for example, when breaking glass.
Conclusion
Thus, it becomes clear how important various sensors are for cars. Without them, the operation of the engine and the machine as a whole would be much more difficult, and fuel consumption, as well as exhaust gas toxicity, would greatly increase. As for car alarms and emergency call systems, their importance is generally difficult to underestimate. These devices help to save lives and save the car.
- 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 accuracy processing, down 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.
First of all, it is necessary to make a distinction between the concepts of "sensor" and "sensor". A sensor is traditionally understood as a device capable of converting the input action of any physical quantity into a signal convenient for further use. Today there are a number of requirements for modern sensors:
- Unambiguous dependence of the output value on the input.
- Stable readings regardless of the time of use.
- High sensitivity.
- small size and small mass.
- Lack of sensor influence on the controlled process.
- Ability to work in various conditions.
- Compatibility with other devices.
Any sensor includes the following elements: a sensitive element and a signaling device. In some cases, an amplifier and a signal selector can be added, but often there is no need for them. The components of the sensor determine the principle of its further operation. At that moment, when any changes occur in the object of observation, they are fixed by a sensitive element. Immediately after this, the changes are displayed on the signaling device, the data of which is objective and informative, but cannot be processed automatically.
Rice. 22.
An example of the simplest sensor is a mercury thermometer. Mercury is used as a sensitive element, the temperature scale acts as a signaling device, and the temperature is the object of observation. It is important to understand that the sensor readings are a set of data, not information. They are not saved to external or internal memory and are not suitable for automated processing, storage and transmission.
All sensors used by various technological solutions from the Internet of Things can be divided into several categories. The basis of one of the most convenient classifications is the purpose of devices "3:
- presence and motion sensors;
- position, displacement and level detectors;
- speed and acceleration sensors;
- force and touch sensors;
- Pressure Sensors;
- flow meters;
- acoustic sensors;
- humidity sensors;
- light detectors;
- temperature sensors;
- chemical and biological sensors.
The operation of sensors is very different from the operation of sensors. First of all, it is necessary to dwell on the definition of the concept of "sensor". A sensor is a device capable of converting changes that have occurred in the object of observation into an information signal suitable for further storage, processing and transmission.
The sensor operation scheme is close to the chain characteristic of the sensor. In a certain sense, the sensor can be interpreted as an improved sensor, since its structure can be expressed as "sensor components" + "information processing unit". The functional diagram of the sensor is as follows.
Rice. 23.
At the same time, the classification of sensors by purpose is equivalent to the same classification for sensors. Often, sensors and transducers can measure the same value for the same object, but the sensors will display the data, and the sensors will also convert them into an information signal.
In addition, there is a special type of sensor that makes sense to consider for understanding the concept of the Internet of things. These are the so-called "smart" sensors, the functional diagram of which is complemented by the presence of algorithms for the primary processing of the collected information. Thus, a conventional sensor is able to process data and provide it in the form of information, while a “smart” sensor is able to perform any actions with self-captured information from the external environment.
In the future, we can expect a serious development of 3D sensors capable of high precision scan the surrounding space and build its virtual model. So, at the moment, the Capri 3D sensor is able to determine the movements of people and their metric characteristics.
teristics. In addition, this sensor can scan an object of the environment and save the information in a SAE file for further sending to print on a 3D printer.
Rice. 24. Capri 3D sensor connected to Samsung Nexus 10
The development of devices that combine several sensors at once deserves special attention. different type. As mentioned in paragraph 2.2.1, in order to obtain knowledge, information is needed about various characteristics of the object. And the use of different sensors allows you to get the necessary information. In a sense, such devices can actually recognize people. An example of such a device is the Kinekt wireless controller used in modern video games.
IR Emitter Color Sensor
Microphone array
Rice. 25. Kinekt 57 wireless controller design
The Kinekt controller contains several components at once: an infrared emitter; infrared receiver; color camera;
set of 4 microphones and processor sound signal; tilt corrector.
The principle of operation of the Klpek controller! simple enough. The rays leaving the infrared emitter are reflected and enter the infrared receiver. Due to this, it is possible to obtain information about the spatial position of a person who plays a video game. The camera is capable of capturing various color data, and the microphones are able to pick up the player's voice commands. As a result, the controller is able to collect enough information about the person so that he can control the game through movements or voice commands.
In a sense, the Ktec controller! belongs to the field of Internet of Things technologies. He is able to identify the player, collect information about him and transfer to other devices (game console). But such a set of sensors can potentially be used in other promising areas for the concept of the Internet of things, including the deployment of smart home technologies.