Limit switch: in the instrument and principle of operation

Virtually all such systems include automated device, such as a limit switch, is responsible for their shutdown when the movable portion to a point. The lighting control systems, limit switches are used as sensors. In the event of circumstances they preset signal is formed.

We will tell you all about functionality and terminal variants disable the device. In the present article we describe proven wiring diagrams, lists the wiring rules. Are the features of the markings are given advice on choosing.

What are the limit switches?

Switches kontseviki - electrical devices for operating the opening and closing a circuit. Their mounted on moving mechanisms for limiting the movement in the predetermined limits. Functions that operate these devices are identical to standard switch.

Filling limit switch is enclosed in a rugged housing, usually metal. All its elements are optimized for easy mounting and easy orientation in space.

Bright, different colors LEDs allow you to monitor the power supply and sensor operation. Two pairs of contacts, usually available in the trailer, make it possible to monitor the state of its connections.

If a closed pair of signal transmission should not be his return, this indicates a malfunction of the cable leading to the switch. After operation of the sensor for the signal may use an open pair of contacts.

Sensitive sensors are the basis in Protection systems against leaks. When water is detected, to identify which they are intended, the device not only signal the maturing emergency in sound and color mode, but also block the operation of the systems in which water is transported.

Classification on the basis of the action

There are three main groups of limit switches: mechanical, non-contact, magnetic. The main function of these devices - automatically disconnecting the working mechanism at the time of reaching a fixed position of its movable part. These switches are used not only for open circuit, but also for its connection.

circuit work Konev sensors is coordinated by two methods: a direct impact on the mobile contacts and position management. In the first case they are called contact, in the second - contactless. An example of a limit switch contact sensors are responsible for closing vehicle doors.

Sensors of this type can not just turn on and off mechanisms, but also to establish the position of the control object. These include float switchesAs well as sensors which determine the fuel level. The signal for the triggering of them serves as resistance change corresponding to the determined liquid level.

Less contact sensors in the presence of mechanical moving parts, a relatively short service life due to ineffective protection against moisture and dust. Advantage - simple design, installation and operation. Significantly better protected against external influences proximity switches. Longer is their resource.

Kontseviki mechanical type

Management of end fitting of this type is a roller or a lever. They are triggered as soon as a control mechanism in the form of a wheel, a button or lever is experienced by mechanical action.

Thus there is a change in the contact position - they are open or closed. The process is accompanied by the signal - a control or warning.

The most common limit switches have two contacts - indoor and outdoor. There are single-end devices, but they rarely occur. In any case, the contacts are in each case, and the operating circuit with their numbers displayed on the panel.

Design inline VC provided off by pressing the actuator button in the form of a small rod. Since it is associated with the dynamic contacts in the contact point there is a disconnection supply chain.

Unlike lever switches it is that their movable contacts or by means of rods through rod associated with a small lever. The action takes place when the actuator pushes on the lever.

In addition to standard terminal devices exist microswitches. They work on the same principle, but the adjustment of the installation requires greater accuracy due to small stroke. To increase the stroke resorted to such a reception, the inclusion in the circuit intermediate element - with the roller lever.

Apply this type of switches, both at work and at home. In the elevator constructions used a large number of QA.

Among them switch to a sensor, limiting the minimum and maximum height of lift travel, signals a rope breakage, signals the opening of the doors and perform many more actions. On the door in many apartments there are micro-switches, turn on the light in the room when you open it.

In such vehicles include mechanical limit sensors in the signaling and lighting circuits. Their feature is the presence of one input connected to it a positive potential. Minus terminal housing is pressed against the metal member on the vehicle body free from paint.

With this vehicle earth element connected cable. The main condition -vyklyuchatel should not come in contact with a wet surface. Sensors connected end for mounting automotive signaling using scheme. Their outputs are allowed to install both on the doors and in the interior on light fixtures.

To switch happened when the door is opened and off when it is closed, perform circuit to positive. Terminal block in the presence of illumination of the ceiling and interior doors is used, performing various functions. As a result, operation block important sensors are blocked when attempting to open the lock.

Features contactless limit switches

One of the limit switches are varieties of noncontact modification (IOO). communication devices configured to actuate when enters the sensitivity zone of a certain object.

Moving parts in the device is not present, and no mechanical contact between the object and configured to impact it switch element.

BVK consists of the following components:

• sensing element;
• a power key;
• component that analyzes the signal.

The distance at which the device begins to operate, is set based on the modification of the sensor and process requirements. Excluding it from both moving and rubbing elements significantly increases the reliability of these devices.

Proximity sensors, or as they are called approximations have extensive functionality. There are two categories - switches and encoders.

The first task of BVK - detect the position of the object. Furthermore, the sensor performs counting, positioning, separation, sorting facilities. He can control the speed of movement to calculate the angle of rotation, skew adjust, and perform many other activities.

In a domestic environment proximity switches while primarily used in lighting control organization. However, in the field of arrangement systems "Smart House" he has a much larger scope and more prospects.

Sensitive devices used in industry, in the transport sector as automation element in refining. According to the principle of detection of approaching objects distinguish BKV inductive, capacitive, optical, ultrasonic.

Inductive proximity sensors

They are set to materials such as metal and amorphous. Among the reactive metal has options for magnetic, ferromagnetic. Within the sensor is a core - a metal or magnetized.

If such a sensor construction described in more detail, it consists of a transmitter, comprising a copper coil located in a ferrite cup. Its functions include redirecting electromagnetic vector lines on the facade of the switch.

The oscillator in the circuit may be either a fixed, negative resistance, and any other type. The magnetic field lines are oriented perpendicular to the direction of the current flowing through the coils of the magnetized core.

The alternating force field due to the alternating voltage at the inputs of the core. The next important junction - signal generator that generates hysteresis and range of the control signal. It includes a detector, which is controlled by the trigger.

The key point of functioning of the inductive limit switch is changes occurring during the approximation or removal of the object. Once the voltage threshold exceeds the permissible value, the sensor is triggered by connecting the trigger key opening.

Capacitive proximity limit switches

After the appearance of the object contour vibrator capacitive device starts the predetermined time parameters. With the approach of the object to the sensor is increasing the capacity of the latter, and the frequency generated by multivibrator reduced.

Once the frequency threshold is exceeded, the unit will turn off. According to this principle, there are many models motion sensors, Disable and enable the bulb when the object is detected in the sensitivity zone.

Structural capacitive sensor circuit is similar to the inductive device: In both models, there is a generator and the detector.

Furthermore generator generating an electric field in their basic design includes such parts as a demodulator. He plays the role of high-frequency oscillations of the amplitude converter with simultaneous change of voltage. Another important component - the trigger is responsible for determining the level of signal and switching hysteresis dependence.

To increase the input signal to the set value in the switch circuit includes a capacitive amplifier. For control of the settings and operation of the device corresponds to the LED.

From moisture and ingress of solid particles to protect the switch element such as a compound. Plastic or brass body protects whatever is inside it from mechanical damage. The kit also includes fasteners.

The switching element in this device is on and the capacitor is a plate which cooperates with the vibrator. The role of the threshold element performs a comparator connected to the vibrator. The latter, in turn, is connected to the frequency converter and voltage.

Unlike capacitive models to inductive is the first to respond to the humidity and density change. Second - to such influences insensitive.

Apparatus ultrasonic switches

The design of the ultrasonic limit switch provides for a quartz sound emitters, forming pulsed wave length of 100 - 500 KSC and a receiver, which correspond to a particular configuration frequency.

When changing the amplitude of the sound waves resulting from maneuvers of the moving object, the microswitch IOO and fixes the new values ​​on the basis of the output signals controls.

The principle of operation of ultrasonic sensors based on the change time during which the sound wave travels from the sensor to the controlled object. Distance detection of such devices is quite large - up to 10 m more of their advantage is that they can detect objects of any shape and color, which reflects the sound..

Such sensors are used to identify objects with a flat surface, which occupies a perpendicular position with respect to the median line detection.

Inaccuracies in their work can cause:

1. Suddenly emerging air streams high power, amplify or attenuate the wave.
2. The sharp change in temperature. When a large amount of heat emitted by the object, the velocity of the propagating wave is changed.
3. The deviation from the vertical angle between the horizontal plane and the object sensor axis. If this error exceeds 10⁰, sensor does not work.
4. Angular shape of the object. In this case, it is very difficult to identify.

Oscillations propagate in a solid, gaseous, liquid medium, and the speed depends on the respective parameters. Ultrasonic sensors have no moving parts, so there is no relationship between the number of cycles and the life of the appliance. They are characterized by high resistance to the effects of any kind of outside.

Optical proximity device

BKV this type of controlled items as overlapping radiation and reflect it. When an object enters the space between the switch and the light source, sensor interrupts the light beam. The element responsible for this action can be a relay or a semiconductor. Radius response extends to 150 m.

Proximity sensors operate in a wide temperature range - -60 to + 150⁰S. They can withstand a pressure of about 500 atm, can be used in hostile environments, and even under conditions of high explosive.

Magnetic end varieties

This type of circuit which is another name for float or reed switches, gradually replacing the mechanical models. Their contacts change position when they are at some distance from the magnet. When this signal is supplied to the control circuit.

The Reed switch is present, one or two blades made of special material - ferromagnet. Magnetic trailer has small dimensions. Is placed in a housing made of plastic or glass, and an electrical circuit mounted in its gap.

Contacts in such a switch can be open, closed, switchable. In devices of the first type of contact is closed when triggered. Normally closed contacts are opened in similar circumstances, and the switching behavior for the situation.

The choice of model depends on the specific circumstances. Reed switches are used in the design of sliding gates. They help stop the construction is done when it reaches its end position when opening or closing.

Some models use a float, as part of the security alarm at the house entrance. When the door is closed, the circuit is closed due to the influence of the magnetic field on the trailer. Opening the door triggers the movement of the magnet and opening of the contact, causing switch signaling.

The fact that the mechanical contact in this design is not, is its advantage, which increases longevity. They are distinguished by a very simple structure, based on the interaction of magnetic contacts with an ordinary magnet.

Regulations and specific connection

Although in themselves limit switches are arranged quite simply, they use them in the equipment with complex electrical circuits. Consequently, their connection must be carried out by specialists and strictly according to the concept, based on the features of technology.

Consider the example of a simple mechanical switch connecting a 3D printer. It is necessary to define the extreme position for his carriage. In the connected trailer available 3 contacts - COM, NO, NC. When you open the sensor state, the first and last contacts are under voltage + 5V. The second contact (NO) is grounded.

Connect the sensor with two wires - red and black. When the device is activated, it should go off the typical click. Indicator switch connected in the same way, but he has a third wire - green.

Its actuation signals A lit LED and click. Its on-board connectors have the notation for the red wire V (+5 V) for black - G (ground) to the green - S (signal).

The same letters denote connectors and optical switch. He will more accurately monitor the performance of the carriage, but may falter with dust and sunlight. Actuation of the optical pair is accompanied by a light emitting diode and switching it takes place noiselessly.

Limit switches are widely used furniture makers, setting them in cabinets coupe. The connection is performed according to the instructions attached to each model. In the diagram, indicate the place of fastening plastic construction with a key. For the middle door to install it should be so that it is not a hindrance for the correct movement of the other door section of the guide.

The installation of the limit switch for swing door, it is fixed with screws inside the cabinet. When closed, the door presses the button opens the circuit and the light is not on. In the open - door releases the button and the light comes on.

Marking the limit switches

Each of the switching devices has a corresponding label. Decrypt it, you can get all the information about the specific model of the limit switch. If it has a record VU222M, it means that before you switch terminal VU222 series. The movable element - the lever modernized.

Details decipher for example marking VP 15M4221-54U2 switch. It is equipped with a movable element of the current series of 15. It has one normally open contact and one normally closed, equipped with a roller tappet.

Protection level - IP54 on the drive side, "Y" represents a climatic modification, and figure 2 - Accommodation category. The product complies with TU U 31.2-25019584-005-2004.

Leading manufacturers in the segment

Producing such sensors many firms. They have a number of recognized leaders. Among them, the German company Sick, as the main producer of such high quality products. Autonics company supplies the market with end-proximity switches inductive and capacitive types.

Contactless high-quality sensors manufactured by Russian company "TECO". They are characterized by ultra-high tightness (IP 68). These limit switches are working in the most hazardous environments including explosive, available in different mounting methods.

Popular limit switches Ukrainian producer "Promfaktor". It produces switches and switches terminal VP, PP, RT. Guarantee, subject to all operational rules is 3 years.

Conclusions and useful videos on the topic

Video # 1. Popularly about the limit switch:

Video # 2. Installation HF on a homemade CNC:

Appointment of the limit switches can be very different. Apply them as in complex industrial systems, and at home to improve our comfort. The main thing is their connection to the electric circuit should only be done after a full stress relief.

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