Do-it-yourself inductive ruler. Contactless sensors. How does an inductive sensor work?

Here I separately brought out such an important practical question, like connecting inductive sensors with transistor output, which in modern industrial equipment– everywhere. In addition, real instructions for the sensors and links to examples are provided.

The principle of activation (operation) of sensors can be anything - inductive (proximity), optical (photoelectric), etc.

The first part described possible options sensor outputs. There should be no problems connecting sensors with contacts (relay output). But with transistor ones and connecting to a controller, not everything is so simple.

Connection diagrams for PNP and NPN sensors

The difference between PNP and NPN sensors is that they switch different poles of the power source. PNP (from the word “Positive”) switches the positive output of the power supply, NPN – negative.

Below, as an example, are diagrams for connecting sensors with a transistor output. Load – as a rule, this is the controller input.

Sensor. The load (Load) is constantly connected to “minus” (0V), the supply of discrete “1” (+V) is switched by a transistor. NO or NC sensor – depends on the control circuit (Main circuit)

Sensor. The load (Load) is constantly connected to the “plus” (+V). Here, the active level (discrete “1”) at the sensor output is low (0V), while the load is supplied with power through the opened transistor.

I urge everyone not to get confused; the operation of these schemes will be described in detail below.

The diagrams below show basically the same thing. Emphasis is placed on the differences in the PNP and NPN output circuits.

Connection diagrams for NPN and PNP sensor outputs

In the left picture there is a sensor with an output transistor NPN. Switched common wire, which in this case is the negative wire of the power supply.

On the right is the case with a transistor PNP at the exit. This case is the most common, since in modern electronics it is customary to make the negative wire of the power supply common, and activate the inputs of controllers and other recording devices with a positive potential.

How to check an inductive sensor?

To do this, you need to supply power to it, that is, connect it to the circuit. Then – activate (initiate) it. When activated, the indicator will light up. But the indication does not guarantee proper operation inductive sensor. You need to connect the load and measure the voltage on it to be 100% sure.

Replacing sensors

As I already wrote, there are fundamentally 4 types of sensors with transistor output, which are divided according to internal structure and connection diagram:

• PNP NO
• PNP NC
• NPN NO
• NPN NC

All these types of sensors can be replaced with each other, i.e. they are interchangeable.

This is implemented in the following ways:

• Alteration of the initiation device - the design is mechanically changed.
• Changing the existing sensor connection circuit.
• Switching the type of sensor output (if there are such switches on the sensor body).
• Program reprogramming – changing the active level of a given input, changing the program algorithm.

Below is an example of how you can replace a PNP sensor with an NPN one by changing the connection diagram:

PNP-NPN interchangeability schemes. On the left is the original diagram, on the right is the modified one.

Understanding the operation of these circuits will help you understand the fact that the transistor is a key element that can be represented by ordinary relay contacts (examples are below in the notation).

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So, here's the diagram on the left. Let's assume that the sensor type is NO. Then (regardless of the type of transistor at the output), when the sensor is not active, its output “contacts” are open and no current flows through them. When the sensor is active, the contacts are closed, with all the ensuing consequences. More precisely, with current flowing through these contacts)). The current flowing creates a voltage drop across the load.

The internal load is shown with a dotted line for a reason. This resistor exists, but its presence does not guarantee stable operation of the sensor; the sensor must be connected to the controller input or other load. The resistance of this input is the main load.

If there is no internal load in the sensor, and the collector “hangs in the air,” then this is called an “open collector circuit.” This circuit ONLY works with a connected load.

So, in a circuit with a PNP output, when activated, voltage (+V) is supplied to the controller input through an open transistor, and it is activated. How can we achieve the same with NPN output?

There are situations when the required sensor is not at hand, and the machine must work “right now”.

We look at the changes in the diagram on the right. First of all, the operating mode of the sensor output transistor is ensured. To do this, an additional resistor is added to the circuit; its resistance is usually about 5.1 - 10 kOhm. Now, when the sensor is not active, voltage (+V) is supplied to the controller input through an additional resistor, and the controller input is activated. When the sensor is active, there is a discrete “0” at the controller input, since the controller input is shunted by an open NPN transistor, and almost all of the additional resistor current passes through this transistor.

In this case, a rephasing of the sensor operation occurs. But the sensor works in mode, and the controller receives information. In most cases this is enough. For example, in the pulse counting mode - a tachometer, or the number of workpieces.

Yes, not exactly what we wanted, and interchangeability schemes for npn and pnp sensors are not always acceptable.

How to achieve full functionality? Method 1 – mechanically move or remake the metal plate (activator). Or the light gap, if we are talking about an optical sensor. Method 2 – reprogram the controller input so that discrete “0” is the active state of the controller, and “1” is the passive state. If you have a laptop at hand, then the second method is both faster and easier.

Proximity sensor symbol

On circuit diagrams Inductive sensors (proximity sensors) are designated differently. But the main thing is that there is a square rotated by 45° and two vertical lines in it. As in the diagrams shown below.

NO NC sensors. Schematic diagrams.

On top diagram– normally open (NO) contact (conventionally designated PNP transistor). The second circuit is normally closed, and the third circuit is both contacts in one housing.

Color coding of sensor leads

Exists standard system sensor markings. All manufacturers currently adhere to it.

However, before installation, it is a good idea to make sure that the connection is correct by referring to the connection manual (instructions). In addition, as a rule, the wire colors are indicated on the sensor itself, if its size allows.

This is the marking.

• Blue – Power minus
• Brown – Plus
• Black – Output
• White – second output, or control input, you need to look at the instructions.

Designation system for inductive sensors

The sensor type is indicated by a digital-alphabetic code, which encodes the main parameters of the sensor. Below is the labeling system for popular Autonics sensors. / Catalog of Omron proximity sensors, pdf, 1.14 MB, downloaded: 1247 times./

/ How can you replace TEKO sensors, pdf, 179.92 kB, downloaded: 1004 times./

/ Sensors from Turck, pdf, 4.13 MB, downloaded: 1336 times./

/ Scheme for connecting sensors using PNP and NPN schemes in the Splan program/ Source file., rar, 2.18 kB, downloaded: 2163 times./

Real sensors

It is problematic to buy sensors, the product is specific, and electricians do not sell these in stores. Alternatively, you can buy them in China, on AliExpress.

Here are the ones I encounter in my work.

Thank you all for your attention, I look forward to questions about connecting sensors in the comments!

Work for manufacturing enterprises requires partial or complete automation of the system. For this, various devices are used to ensure uninterrupted operation. Metal devices are often monitored by inductive proximity sensors, which have their own advantages and disadvantages. They have small size and perform their function well if connected correctly.

General information

The induction sensor is special device, related to non-contact. This means that to determine the location of an object in space, it does not require direct contact with it. Thanks to this technology, automation of the production process is possible.

As a rule, the device is used in various lines and systems in large plants and factories. It can also be used as a limit switch. The device is of high quality and reliability, works even in difficult conditions. It only affects metal objects, since other materials are insensitive to it.

The device is quite resistant to aggressive chemicals, is widely used in the engineering, food and textile industries. The aerospace, military and railway industries also need these sensors.

The importance of the device makes it in demand, so many companies around the world produce various models with a standard and extended set of functions, in different price categories.

Device structure

Inductive sensor consists of several interconnected nodes that ensure its smooth operation . The main details of the device are as follows:

All elements are located in a housing made of brass or polyamide. These materials are considered very durable in order to protect the core from the negative effects of manufacturing conditions. Thanks to the reliability of the design, The sensor can withstand significant load and still function correctly.

Principle of operation

Thanks to a special generator that produces special vibrations, the device operates. When an object made of metal enters its field of action, a signal is sent to the control unit.

The operation of the device begins after switching on, which gives impetus to the formation magnetic field. This field, in turn, influences eddy currents that change the amplitude of oscillations of the generator, which is the first to respond to any changes.

As soon as a signal arrives, it begins processing in other nodes of the device. The strength of this signal largely depends on the size of the object that falls within the field of action of the device, as well as the distance at which it is located. The next step is to convert the analog signal to logic. This is the only way to accurately determine its meaning.

Such sensors play a special role in production, Where metal parts must follow a line in a certain position. The device can record it and if any, even minor, deviation is detected, it signals to the main control panel.

As a rule, reading the results of the operation of the device is carried out by a specialist who also plays the role of a controller monitoring the smooth operation of the entire system.

Basic definitions

There are several definitions for monitoring the operation of a device and reading its signals. The following are considered the most important:

Thanks to these definitions, it is possible to configure the device to obtain the most accurate data, which plays an important role in the production process.

Advantages and disadvantages

Induction sensors have their advantages and disadvantages, like any other device. The main advantage is the simplicity of the design, which does not require complex settings and does not require special conditions for installation. The device has no sliding contacts and is made of durable material and can work for a long time without interruption.

It is also worth noting that the device very rarely fails, and repairing it is not difficult. That is why it is often installed in enterprises where almost round-the-clock monitoring is required. production process. Contactless connection allows for hassle-free connection with industrial system voltage.

An important advantage is considered to be high sensitivity, which allows the sensors to be installed in production, where they work with metal objects made of different alloys.

Despite all the advantages of the device, there are some disadvantages. The most important are the errors that the device produces in operation. The nonlinear type of error manifests itself due to the fact that the device has its own indicator of the inductive quantity, which may differ from the value of the objects to which it reacts. This is why the sensor may not react correctly to metal and give incorrect signals.

Often meets temperature error associated with a significant decrease or increase in temperature in production premises. The instructions for the device assume its correct functioning at +25 degrees. If the value deviates in one direction or another, the operation of the device is disrupted.

One of the random errors is considered to be a change in sensor readings due to the influence of the electromagnetic field of other devices on it. In order to avoid such situations, a frequency standard for electrical installations of 50 Hz has been established in all industries. In this case, the risk of errors due to extraneous electromagnetic radiation is reduced to a minimum. Any malfunctions in the operation of the device can be eliminated by preliminary work on the parts.

Connection methods

Depending on the type of device, the methods of connecting it differ, since certain varieties have different quantities wires Two-wire ones are considered the simplest, but also the most problematic option. Connected directly to the current load circuit. For correct implementation manipulation requires a nominal load resistance. If it decreases or increases, the device begins to function incorrectly. An important point There will be a network connection in which polarity must be observed.

Three-wire ones are considered the most popular and easiest to connect. Some wires are connected to the load, and the other two to the voltage source. This eliminates the possibility of the device reacting to the nominal resistance in the form of incorrect operation.

There are also sensors with four and five wires. When installing them, two wires are connected to the voltage source, two - to the load. If there is a fifth cord, then it is possible to select the appropriate operating mode.

Usually the wires are designated different colors to facilitate installation and subsequent maintenance of the sensor. Minus and plus are indicated in blue and red, respectively. The output is always marked black. There are devices that have two outputs. The second one is usually white and can also serve as an entrance. These nuances are indicated in the operating instructions for the inductive sensor.

The device body can be made of different materials, have a cylindrical, square or rectangular shape. The first option is considered the most common.

Selection rules

The induction sensor is considered important element in many enterprises, so its choice should be approached very responsibly. It is recommended to follow the following rules:

An important parameter is the cost of the device. It most often depends on the manufacturer and some additional functions, which are built into the sensor. However, there is no significant difference in performance between devices from different price categories.

Popular models

There are many models of inductive sensors on the market today. The most popular are various devices from Russian company TEKO. They differ good quality, excellent technical characteristics, ease of installation and operation. The main advantage of the company's devices is their affordable price.

Price simple models starts at 850 rubles, and for this money the device works flawlessly. More expensive sensors are also produced with prices ranging from 2 to 5 thousand rubles. They are usually installed in large industries where high precision and uninterrupted operation are required.

The induction sensor is considered one of the best non-contact devices used in various plants, factories and other enterprises. High quality and the accuracy of the device makes it popular and necessary.

What's happened capacitive sensors? This is the most common electronic relay that is triggered when the capacitance changes. The sensitive element of many of the circuits discussed here are high-frequency oscillators of hundreds of kilohertz or more. If you connect an additional capacitance in parallel to the circuit of this generator, then either the frequency of the generator will change, or its oscillations will stop completely. In any case, a threshold device will work, which turns on a sound or light alarm. These schemes can be used in various models, which, when encountering various obstacles, will change their movement, in everyday life - sat in computer chair laptop turned on or started playing music Center, the devices can also be used to turn on lights in rooms to build alarm systems, etc.

The circuit operates at audio frequencies. To increase sensitivity, a field-effect transistor is added to the low-frequency generator circuit.

Generator of rectangular pulses with the repetition frequency of the latter 1 kHz made on elements DD1.1 And DD1.2. Designed as an output stage DD1.3, the load of which is the telephone speaker.

In order to increase the sensitivity of the circuit, you can add the number of radio components introduced into RC - chain.

The circuit should start working immediately after switching on. Sometimes you need to adjust the resistance R1 to threshold sensitivity.

When adjusting a relay, two options for its operation are possible: failure or generation when a capacitance appears. The installation of the circuit design option we need is selected by selecting the nominal value variable resistance R1. When your hand approaches E1 by adjusting resistance R1, they make it so that the distance from which the circuit is started is 10 - 20 centimeters.

To turn on various actuators in a capacitive relay, we use the signal from the element output DD1.3.

To turn on the light, they pass next to the second capacitive converter, and to turn off the lighting in the room, they pass next to the first.

Triggering of the converter leads to switching of the RS trigger built on logical elements. Capacitive sensors are made from pieces of coaxial cable, from the end of which a screen is removed for a length of about 50 centimeters. The edge of the screen needs to be insulated. The sensors are installed on the door frame. The length of the unshielded part of the sensors and the resistance values ​​R5 and R6 are selected when debugging the circuit so that the trigger is reliably triggered when a biological object passes at a distance of 10 centimeters from the sensor.

While the capacitance between the sensor and the housing is small, short pulses of positive polarity are formed at the resistance R2 and at the input of the element DD1.3, and at the output of the element the same pulses are already inverted. Capacitance C5 is slowly charged through resistance R3 when there is a logical one level at the element’s output, and quickly discharges through diode VD1 at logical zero. Since the discharge current is higher than the charging current, the voltage on capacitor C5 has a logical zero level, and element DD1.4 is locked for the audio frequency signal.

When approaching an element of any biological object, its capacitance relative to the common wire increases, the amplitude of the pulses at resistance R2 drops below the switching threshold DD1.3. At its output there will be a constant logical one; capacitor C5 will be filled with capacitance to this level. Element DD1.4 will begin to transmit an audio frequency signal, and the speaker will hear sound signal. The sensitivity of the capacitive relay can be adjusted by adjusting capacitance C3.

The sensor is made by hand using metal mesh with dimensions of 20 x 20 centimeters, for a good level of relay sensitivity.

In this capacitive relay circuit, a transistor VT1 is connected to the logical element DD1.4, in the collector circuit of which a thyristor VS1 is connected to control a powerful load.

The device, assembled according to the diagram below, reacts to the presence of any conductive object, including a person. The sensitivity of the sensor can be adjusted using a potentiometer. The circuit does not allow detecting the movement of objects, but it is good precisely as a presence sensor. One of the obvious solutions for using a capacitive presence sensor in everyday life is homemade circuit automatic door opening. For these purposes, the device diagram must be placed on the front of the door.

The basis of this capacitive device is an oscillator with T1 and a one-shot device. The oscillator is a typical Clapp oscillator with a stable frequency. The capacitive sensor surface acts as a capacitor for the tank circuit, and in this configuration the frequency will be around 1 MHz.

The switching time of the circuit can be changed over a wide range using variable resistor P2. There is no need to bring metal objects close to the sensor, as the capacitive relay will remain in closed state. This circuit can also be used as a detector of aggressive liquids. The main advantage here is that the surface of the capacitive sensor does not come into direct contact with the liquid.

Made on a field-effect transistor low power generator with a pulse repetition rate of 465 kHz, and on a bipolar transistor electronic key to activate relay K1, the contacts of which turn on the actuator. A diode is used in a circuit when the polarity of the connected power source accidentally changes.

The range of action of the capacitive relay and sensitivity depend on the adjustment of C1 and the design of the sensor, if you are interested in this development, then you can download the model designer magazine from the link just above.

The basis of the circuit is a low-power RF generator. To the oscillatory circuit L1C4 metal plate connected. The palm of a hand or another part of the human body brought to it represents the second plate of the capacitor C d. the higher, the larger the area of ​​its plates and the smaller the distance between them. L1 wind on the frame ∅ 8-9 mm, glued from paper. The coil CONSISTS OF 22-25 turns of PEV-1 0.3-0.4 wire, wound turn to turn. The tap must be made from the 5-7th turn, counting from the beginning.

Connect the bipolar transistor to the collector circuit V1 10 mA milliammeter and between the connection point of the milliammeter to the coil L1 and connect a 0.01-0.5 µF capacitor with the emitter of the second transistor. Temporarily disconnect the metal plate from the generator. Monitoring the readings of the milliammeter, we briefly close L1C4. Collector current V1 drops sharply: from 2.5-3 to 0.5-0.8 mA. The maximum readings correspond to generation, the minimum - its absence. If the generator is excited, attach the plate to it and slowly move your palm towards it. The collector current should drop to a level of 0.5-0.8 mA.

Weak current changes are amplified using a two-stage ULF on V2, V3. And in order to be able to control the load using a contactless method, the final stage of the circuit is built on a trinistor V5.

Variable resistance motor R4 set to the lowest position. And then it is slowly moved up until the indicator turns on H1. Now we bring our palm to the plate and check the operation of the device.

Diode V4 in the thyristor circuit V5 eliminates the appearance of a reverse voltage pulse. A V6 and resistance R7 protect the thyristor from breakdown. For SCR with U o6p. = 400 V elements V6 And R7 can be removed from the diagram.

Inductive proximity sensor. 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 are 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 to the controller or vomits. 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.

Field induction sensor. Metal plate changes resonant frequency oscillatory circuit

Inductive npn sensor circuit. A functional diagram is shown, which shows: a generator with an oscillating circuit, a threshold device (comparator), an NPN output 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– current and voltage matching.

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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 metal plate, which guarantees reliable operation of the sensor. 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 constant voltage it is important to maintain polarity. For sensors designed to work 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” one is switched, or neutral wire. 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 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 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 for various devices and connecting sensors to them, ask in the comments and we’ll think about it together.

Continuation of the article -. In the second part, real diagrams are given and discussed practical use 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... Operating principle optical sensors shown in the picture below

Barrier

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

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

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

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

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

Pros:

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

Minuses:

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

Reflex

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

The operating principle can be seen in the figure below

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

Diffusion

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

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

Capacitive and inductive sensors

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

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

How does an inductive sensor work?

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

So, our guest is an inductive sensor Russian production

We read what is written on it

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

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

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

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

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

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

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

Conclusion

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