Types of position sensors. Automotive sensors: types, installation options, operating features. Classification by manufacturing technology

Inductive sensor approaching. Appearance

In industrial electronics, inductive and other sensors are used very widely.

The article will be a review (if you want, popular science). Real instructions for the sensors and links to examples are provided.

Types of sensors

So, what exactly is a sensor? A sensor is a device that produces a specific signal when a specific event occurs. In other words, the sensor is activated under a certain condition, and an analog (proportional to the input effect) or discrete (binary, digital, i.e. two possible levels) signal appears at its output.

More precisely, we can look at Wikipedia: Sensor (sensor, from the English sensor) is a concept in control systems, a primary transducer, an element of a measuring, signaling, regulating or control device of a system that converts a controlled quantity into a signal convenient for use.

There is also a lot of other information, but I have my own, engineering-electronics-applied, vision of the issue.

There are a great variety of sensors. I will list only those types of sensors that electricians and electronics engineers have to deal with.

Inductive. Activated by the presence of metal in the trigger zone. Other names are proximity sensor, position sensor, inductive, presence sensor, inductive switch, proximity sensor or switch. The meaning is the same, and there is no need to confuse it. In English they write “proximity sensor”. In fact, this is a metal sensor.

Optical. Other names: photosensor, photoelectric sensor, optical switch. These are also used in everyday life, they are called “light sensors”

Capacitive. Triggers the presence of almost any object or substance in the field of activity.

Pressure. There is no air or oil pressure - the signal is sent to the controller or it breaks. This is if discrete. There may be a sensor with a current output, the current of which is proportional to absolute or differential pressure.

Limit switches(electrical sensor). This is a simple passive switch that trips when an object runs over or presses against it.

Sensors may also be called sensors or initiators.

That's enough for now, let's move on to the topic of the article.

The inductive sensor is discrete. The signal at its output appears when metal is present in a given zone.

The proximity sensor is based on a generator with an inductor. Hence the name. When metal appears in the electromagnetic field of the coil, this field changes dramatically, which affects the operation of the circuit.

Induction sensor field. The metal plate changes the resonant frequency of the oscillatory circuit

Inductive npn sensor circuit. Given functional diagram, on which: a generator with an oscillatory circuit, a threshold device (comparator), an output NPN transistor, protective zener diodes and diodes

Most of the pictures in the article are not mine; at the end you can download the sources.

Application of inductive sensor

Inductive proximity sensors are widely used in industrial automation to determine the position of a particular part of the mechanism. The signal from the sensor output can be input to a controller, frequency converter, relay, starter, and so on. The only condition is matching the current and voltage.

Operation of an inductive sensor. The flag moves to the right, and when it reaches the sensor's sensitivity zone, the sensor is triggered.

By the way, sensor manufacturers warn that it is not recommended to connect an incandescent light bulb directly to the sensor output. I have already written about the reasons - .

Characteristics of inductive sensors

How are the sensors different?

Almost everything that is said below applies not only to inductive, but also to optical and capacitive sensors.

Design, type of housing

There are two main options - cylindrical and rectangular. Other housings are used extremely rarely. Case material – metal (various alloys) or plastic.

Cylindrical sensor diameter

Main dimensions – 12 and 18 mm. Other diameters (4, 8, 22, 30 mm) are rarely used.

To secure an 18 mm sensor, you need 2 keys of 22 or 24 mm.

Switching distance (working gap)

This is the distance to the metal plate at which reliable operation of the sensor is guaranteed. For miniature sensors this distance is from 0 to 2 mm, for sensors with a diameter of 12 and 18 mm - up to 4 and 8 mm, for large sensors - up to 20...30 mm.

Number of wires to connect

Let's get to the circuitry.

2-wire. The sensor is connected directly to the load circuit (for example, a starter coil). Just like we turn on the lights at home. Convenient for installation, but capricious in terms of load. They work poorly with both high and low load resistance.

2-wire sensor. Connection diagram

The load can be connected to any wire for DC voltage It is important to observe polarity. For sensors designed to operate with alternating voltage, neither the load connection nor the polarity matters. You don't have to think about how to connect them at all. The main thing is to provide current.

3-wire. The most common. There are two wires for power and one for load. I'll tell you more separately.

4- and 5-wire. This is possible if two load outputs are used (for example, PNP and NPN (transistor), or switching (relay). The fifth wire is the choice of operating mode or output state.

Types of sensor outputs by polarity

All discrete sensors can have only 3 types of outputs depending on the key (output) element:

Relay. Everything is clear here. The relay switches the required voltage or one of the power wires. This ensures complete galvanic isolation from the sensor power circuit, which is the main advantage of such a circuit. That is, regardless of the sensor supply voltage, you can turn on/off the load with any voltage. Mainly used in large-sized sensors.

Transistor PNP. This is a PNP sensor. The output is a PNP transistor, that is, the “positive” wire is switched. The load is constantly connected to “minus”.

Transistor NPN.At the output there is an NPN transistor, that is, the “negative” or neutral wire is switched. The load is constantly connected to the “plus”.

You can clearly understand the difference by understanding the principle of operation and switching circuits of transistors. The following rule will help: Where the emitter is connected, that wire is switched. The other wire is connected to the load permanently.

Below will be given sensor connection diagrams, which will clearly show these differences.

Types of sensors by output status (NC and NO)

Whatever the sensor, one of its main parameters is the electrical state of the output at the moment when the sensor is not activated (no impact is made on it).

The output at this moment can be turned on (power is supplied to the load) or turned off. Accordingly, they say - a normally closed (normally closed, NC) contact or a normally open (NO) contact. In foreign equipment, respectively – NC and NO.

That is, the main thing you need to know about the transistor outputs of sensors is that there can be 4 types of them, depending on the polarity of the output transistor and the initial state of the output:

• PNP NO
• PNP NC
• NPN NO
• NPN NC

Positive and negative logic of work

This concept refers rather to actuators that are connected to sensors (controllers, relays).

NEGATIVE or POSITIVE logic refers to the voltage level that activates the input.

NEGATIVE logic: the controller input is activated (logic “1”) when connected to GROUND. The S/S terminal of the controller (common wire for discrete inputs) must be connected to +24 VDC. Negative logic is used for NPN type sensors.

POSITIVE logic: the input is activated when connected to +24 VDC. The S/S controller terminal must be connected to GROUND. Use positive logic for PNP type sensors. Positive logic is used most often.

There are options various devices and connecting sensors to them, ask in the comments, we’ll think about it together.

Continuation of the article -. In the second part, real diagrams are given and discussed practical application various types sensors with transistor output.

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

Optical sensor

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

Barrier

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

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

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

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

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

Pros:

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

Cons:

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

Reflex

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

The operating principle can be seen in the figure below

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

Diffusion

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

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

Capacitive and inductive sensors

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

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

How does an inductive sensor work?

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

So, our guest is a Russian-made inductive sensor

We read what is written on it

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

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

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

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

The moment of truth comes... We bring a metal object to the working area of ​​the sensor, and our sensor immediately triggers, 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, when the sensor is triggered, it produces a logical one signal, which can be used in digital devices.

Conclusion

In the world of electronics, these three types of sensors are increasingly used. Every year the production of these sensors is growing and growing. They are used in completely different areas of industry. Automation and robotization would not be possible without these sensors. In this article, I analyzed only the simplest sensors that give us only an “on-off” signal, or, to put it in English, 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 an inductive sensor

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

Here You can look at the variety of inductive sensors.

A modern car consists of many mechanical, electromechanical and electronic components. Optimal performance engine must be provided regardless of external conditions. When changing external factors, the operation of units and components must adapt to them. Vehicle sensors serve as a kind of monitoring device for the operation of the vehicle. Let's look at 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 transferred to the air flow in the engine intake manifold. Heating
The sensor element is installed in front of the vehicle's air filter. Change
air flow speed and, accordingly, its mass fraction, is reflected in the degree
changes in the temperature of the MAF sensor heating coil.

“Trippling” 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

The oxygen sensor or lambda probe determines the amount of oxygen remaining 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 possible malfunction sensor

5. Throttle sensor - signs 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 speed
the engine crankshaft depends on the degree of coolant heating.

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

6. Oil pressure sensor - functions, failure

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

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

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

7. Is the engine knock sensor not working?

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

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

8. Camshaft angle sensor - engine troubles

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

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

9. ABS / ABS sensor in a car - check functionality

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 toothed disk, which is mounted on the wheel hub. If the ABS sensor is faulty, the warning light on the control panel does not go out after starting the engine.

The technology for determining the functionality of the sensor is to measure the resistance between the sensor contacts; if there is a malfunction, the resistance is zero.

10. Fuel level sensor in a car - how to check its functionality?

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 tank. The sensor signals are sent to a dial or electronic indicator on the vehicle control panel. Checking the functionality of the fuel level sensor is carried out with an ohmmeter, which measures the resistance between the sensor contacts.

Elements of automatic control systems

Automation- a branch of science and technology about the management of various processes and control of their progress, carried out without direct human participation.

Managing various processes without human intervention is called automatic control, and the technical means by which it is carried out - by means of automation.

Parameters of the production process that must be constantly maintained or changed according to a certain law are called controlled quantity.

Complex technical means, designed to automate production processes, is automatic system.

Depending on the functions performed, they are distinguished automatic systems control, management and regulation.

Systems consist of a control object and an automatic control device. If the input influences for the control device are only external influences, the system is called open(without feedback), if external and internal - closed(with feedback).

Depending on the method of generating control signals, systems are divided into continuous And discrete(digital).

Automation systems consist of a number of interconnected elements that perform certain functions and provide a comprehensive control process.

In accordance with the functions performed, all elements of the automatic system are divided into three groups:

1) measuring

2) transformative

3) executive

Measuring The group consists of various types of sensors.

Transformative— amplification devices, regulators, digital and microprocessor devices.

Executive— electric motors, contactors, control valves, etc.

Automation elements are called structurally complete devices that perform certain independent functions of signal conversion in automation systems.

Each element converts the energy received from the previous element and transfers it to the next one. Elements can be electrical or non-electric: hydraulic, pneumatic, mechanical, etc.

The most important requirement for automation devices is high reliability. Unreliable operation of the automatic control system (failure or error) can lead to a violation production process and other serious consequences.

Of particular importance is the use of automatic systems in those areas where human capabilities are not able to provide the proper level of control over technological process. This may apply to both rapidly occurring processes (for example, voltage changes) and harmful factors(e.g. nuclear reactions, chemical production).

Automation of various technological processes, control of various machines and mechanisms require numerous measurements of various physical quantities. Information about parameters controlled system or devices are received using sensors or sensors in other ways.

Sensor is a device that converts the input effect of any physical quantity into a signal convenient for further use (most often into an electrical signal).

That. sensors convert your favorite value into an electrical signal, which is convenient to transmit, process, display, etc.

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

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

Currently, there is approximately the following distribution of the share 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%.

2) Based on the type of output value into which the input value is converted, non-electrical and electrical sensors are distinguished. Most sensors are electrical.

3) Based on the principle of operation, sensors can be divided into two classes: generator and parametric (modulator sensors). Generator sensors directly convert the input value into an electrical signal. Parametric sensors convert the input value into a change in any electrical parameter (R, L or C) of the sensor, therefore they require a power source for operation.

Based on the principle of operation, sensors can also be divided into ohmic, thermometric, photoelectric, inductive, capacitive, etc.

There are three classes of sensors:

Analog sensors that produce an analog signal proportional to the change in the input value;

Digital sensors that generate a sequence of pulses or a digital code;

Binary (binary) sensors that produce a signal of only two levels: “on/off” (in other words, 0 or 1).

Ohmic (resistive) sensors—the operating principle is based on a change in their active resistance when the length changes l, cross-sectional area S or resistivity p, i.e.

R=pl/S (1.1)

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

Contact sensors are simplest form resistor sensors that convert the movement of the primary element into an abrupt change in resistance electrical circuit. Contact sensors are used to measure and control forces, movements, position, temperature, dimensions of objects, etc. Contact sensors include travel and limit switches, contact thermometers and so-called electrode sensors, which are mainly used to measure limit levels of electrically conductive liquids.

The disadvantage of contact sensors is the limited service life of the contact system, but due to the simplicity of these sensors they are widely used.

Rheostatic The sensors are a resistor with varying active resistance. 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 movement (angular or linear) needs to be converted.

The most widely used is a potentiometric circuit for switching on a rheostat sensor, in which the rheostat is connected according to a voltage divider circuit (Fig. 1.1). A variable resistor connected according to a voltage divider circuit is called a potentiometer.

The output value U out of such a sensor is the voltage drop between the moving and one of the fixed contacts. The dependence of the output voltage on the movement “x” of the contact U out = f(x) corresponds to the law of resistance change along the potentiometer.

Figure 1.1 — Potentiometric circuit for switching on a rheostat sensor

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

Strain gauges are used to measure mechanical stress, small deformations, and vibration. The action of strain gauges is based on the strain effect, 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.

Thermal resistors are used as sensors 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 cause the thermistor to heat up. Under this condition, the thermistor is used as a temperature sensor.

2) The temperature of the thermistor is determined by the degree of heating by a constant current and cooling conditions. In this case, the established temperature is determined by the conditions of heat transfer from the surface of the thermistor (the speed of movement of the environment - gas or liquid - relative to the thermistor, its density, viscosity and temperature), so the thermistor can be used as a sensor of flow speed, thermal conductivity of the environment, density of gases, etc. p.

Figure 1.2 - Using a self-heating resistor as a flow sensor

For example, to measure the volume of air consumed in automobile engines, a self-heating resistor is installed in the air duct. The resistance of such a resistor changes due to cooling by the air flow, as a result of which the resistor acts as a flow sensor (Fig. 1.2).

Inductive sensors are used to obtain contactless information about the movements of the working parts of machines and mechanisms.

The principle of operation of the sensor is based on changing electromagnetic field when metal objects enter the sensor's coverage area (the sensor does not respond to non-metallic materials). Inductive sensors are mainly used as proximity switches (does not require mechanical action) for position determination (limit and limit switches).

Figure 1.3 shows examples of the use of inductive sensors as position, angle, and speed sensors.

Figure 1.3 - Examples of using an inductive sensor (VBI - non-contact induction switch)

The disadvantages of inductive sensors are their short response distance and relatively low sensitivity.

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

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

C = e 0 eS/h (1.2)

where e 0 is the dielectric constant;

e is the relative dielectric constant of the medium between the plates;

S is the active area of ​​the plates;

h is the distance between the capacitor plates.

The dependence of the capacitance on the area of ​​the plates and the distance between them is used to measure angular movements, very small linear movements, vibrations, movement speed, etc.

Widely capacitive sensors are used to monitor the level of liquids and bulk materials. In this case, it is possible to place the sensors outside the tank or hopper. Material falling into work area sensor, causes a change in dielectric constant e, which changes the capacitance and triggers the sensor (Fig. 1.4).

Figure 1.4 - Capacitive sensor

a) distribution of the electric field of the capacitor,

b) example of minimum and maximum level control

In addition, sensors for the thickness of a layer of non-conducting materials (thickness gauges) and control humidity and composition of the substance work to measure the value of dielectric constant e.

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.

Induction sensors convert the measured value into induced emf. These sensors include tachogenerators, whose output voltage is proportional to the angular speed of rotation of the generator shaft. Used as angular velocity sensors.

The tachogenerator (Fig. 1.5) is an electrical machine operating in generator mode. The controlled object is mechanically connected to the tachogenerator rotor and causes it to rotate. 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 rotation speed, the frequency of the EMF changes.

Figure 1.5 — Tachogenerator

a) design, b) diagrams of input and output EMF

Temperature sensors are the most common; a wide range of measured temperatures, a variety of conditions for using measuring instruments and requirements for them determine the variety of temperature measuring instruments used.

Main classes of temperature sensors for industrial applications: silicon temperature sensors, bimetallic sensors, liquid and gas thermometers, temperature indicators, thermocouples, resistance thermal converters, infrared sensors.

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

A bimetallic sensor is a plate of two dissimilar metals having different temperature coefficient linear expansion. When heated or cooled, the plate bends, opening (closing) electrical contacts or moving the indicator needle. The operating range of bimetallic sensors is -40 to +550 0 C. Used for surface measurement solids and temperature of liquids. The main areas of application are heating and water heating systems.

Thermal indicators are special substances that change their color under the influence of temperature. Produced in the form of films.

Resistance thermal converters (thermistors) are based on changes in the electrical resistance of conductors and semiconductors depending on temperature.

As the temperature rises, the resistance of metals increases. For the manufacture of metal thermistors, copper, nickel, and platinum are used. Platinum thermistors allow you to measure temperatures in the range from -260 to 1100 0 C.

Semiconductor thermistors have a negative or positive temperature coefficient of resistance. In addition, semiconductor thermistors, with very small sizes, have high resistance values ​​(up to 1 MOhm).

They are used to change temperatures in the range from -100 to 200 0 C.

A thermocouple is a connection (junction) of two dissimilar metals. The work is based on the thermoelectric effect - in the presence of a temperature difference between the junction T 1 and the ends of the thermocouple T 0, an electromotive force occurs, called thermo-electromotive (abbreviated thermo-EMF). In a certain temperature range, we can assume that thermo-EMF is directly proportional to the temperature difference ΔT = T 1 - T 0.

Thermocouples make it possible to measure temperatures in the range from -200 to 2200 0 C. The most widely used materials for the manufacture of thermoelectric converters are platinum, platinum-rhodium, chromel, and alumel.

Thermocouples are cheap, easy to manufacture and reliable in operation. Measuring multimeters are equipped with thermocouples.

Infrared sensors (pyrometers) - use radiation energy from heated bodies, which allows you to measure surface temperature at a distance. Pyrometers are divided into radiation, brightness and color. Allows you to measure temperature in hard to reach places and the temperature of moving objects, high temperatures, where other sensors no longer work.

Piezoelectric The sensors are based on 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.

Used to measure forces, pressure, vibration, etc.

Optical (photoelectric) The sensors operate either on the basis of the internal photoelectric effect - a change in resistance when the illumination changes, or they produce a photovoltage proportional to the illumination.

Distinguish analog And discrete optical sensors. With analog sensors, the output signal varies 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 one when a set illumination value is reached.

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

Figure 1.6 - Examples of using photoelectric sensors

Registers a change in the light 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.

Optical proximity sensor consists of two functional units: receiver and emitter. These units can be made either in one housing or in different housings.

There are two methods for detecting an object using photoelectric sensors:

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 operating principle is based on the fact that the transmitter constantly sends out a light beam, which is received by the receiver. If the light signal from the sensor stops due to obstruction by a foreign object, the receiver immediately reacts by changing the output state.

2) Reflection from an object - in this method, the receiver and transmitter are located in the same housing. During the operating state of the sensor, all objects falling into its working area become a kind of reflectors (reflectors). As soon as a light beam reflected from an object hits the sensor receiver, it immediately reacts by changing the output state.

Homework

1) Name what types of sensors and explain why they can be used as position sensors.

2) Name what types of sensors and explain why they can be used as speed sensors.

3) Name what types of sensors and explain why they can be used as sensors - flow meters.

4) The figure shows an inductive sensor.

Write down which sensor parameters and in which direction will change when the anchor moves:

1) up; 2) down; 3) to the right; 4) left.

5) Explain the purpose of the sensor shown in the figure (left).

6) Explain the purpose of the sensors shown in the figure (right). Why are two sensors used?

Electrical Engineering Encyclopedia #16.

Sensors