The proximity switch is a position switch that can operate without mechanical contact with the moving part. When the object approaches the sensing surface of the switch to the action distance, the switch can be actuated without mechanical contact and exerting any pressure, thereby driving the DC electric apparatus. Or provide control instructions to a plc device. Proximity switch is a kind of switch type sensor (namely non-contact switch). It has both the characteristics of limit switch and micro switch, and it has the sensing performance, reliable operation, stable performance, fast frequency response, long service life, and anti-interference. Strong ability, and with waterproof, shockproof, corrosion-resistant and other characteristics. Products are inductive, capacitive, Hall, AC, DC type.
Proximity switch, also known as non-contact proximity switch, is an ideal electronic switch sensor. When the metal detector is close to the sensing area of the switch, the switch can be contactless, no pressure, no spark, quickly send electrical instructions, accurately reflect the position and stroke of the moving mechanism, even if used for general stroke control, positioning accuracy, operation The frequency, the service life, the convenience of installation and adjustment, and the applicability to harsh environments cannot be compared with the general mechanical type of travel switch. It is widely used in machine tools, metallurgy, chemical, textile and printing industries. In the automatic control system can be used as limit, counting, positioning control and automatic protection links.
Among various types of switches, there is a component that has "feel" ability to approach its object - a displacement sensor. This is the proximity switch, which uses the proximity sensor's sensitivity to the proximity of the object to achieve the purpose of turning the switch on and off.
When there is an object moving towards the proximity switch and approaching a certain distance, the displacement sensor only has “perceived” and the switch will act. This distance is usually called the "checkout distance." However, different proximity switches detect different distances.
Sometimes the object to be inspected is moved one by one to the proximity switch and one by one at regular intervals, so that it repeats continuously. Different proximity switches have different response capabilities to detection objects. This response characteristic is called "response frequency".
Because the displacement sensor can be made according to different principles and different methods, and the different sensors have different “perceived” methods for objects, so common proximity switches have the following types:
Passive proximity switch
This switch does not require a power supply and controls the closed state of the switch through magnetic induction. When the magnetic or iron trigger is close to the switching magnetic field, the internal magnetic force of the switch controls the closing. Features: No power, no contact, no maintenance, environmental protection.
Eddy current proximity switch
This type of switch is sometimes called an inductive proximity switch. It is the use of conductive objects in the proximity of this can generate electromagnetic field proximity switches, so that the object generates eddy currents. This eddy current reacts to the proximity switch, causing the internal circuit parameters of the switch to change, thereby recognizing whether or not the conductive object is moving closer, thereby controlling the on and off of the switch. The object that this proximity switch can detect must be a conductor.
1. Principle: An oscillator is composed of an inductor coil, a capacitor and a transistor, and an alternating magnetic field is generated. When a metal object approaches this magnetic field, eddy currents are generated in the metal object, causing the oscillation to stop. This change is caused by After the amplifying process, it is converted into a transistor switching signal output.
2. Features: A, good anti-interference performance, high switching frequency, greater than 200HZ. B, can only sense the metal
3. Applicable to various machinery and equipment for position detection, counting signal picking and so on.
Capacitive proximity switch
The measurement of such a switch is usually one plate constituting a capacitor, and the other plate is the housing of the switch. This enclosure is usually grounded or connected to the enclosure of the device during the measurement process. When an object moves toward the proximity switch, whether it is a conductor or not, due to its proximity, the dielectric constant of the capacitor always changes, so that the capacitance changes, and the state of the circuit connected to the measuring head also occurs. Changes, which can control the switch on or off. The object to be detected by this proximity switch is not limited to a conductor, an insulating liquid, a powder, or the like.
Hall proximity switch
The Hall element is a magnetosensitive element. A switch made using a Hall element is called a Hall switch. When the magnetic object moves close to the Hall switch, the Hall element of the switch detection surface changes the internal circuit state of the switch due to the generation of the Hall effect, thereby recognizing the presence of a magnetic object nearby, thereby controlling the on and off of the switch. The proximity switch must be a magnetic object.
Photoelectric proximity switch
Switch made of photoelectric effect is called photoelectric switch. The light emitting device and the optoelectronic device are mounted in the same test head in a certain direction. When there is a reflective surface (detected object) approaching, the optoelectronic device receives the reflected light and then outputs the signal, thereby "sensing" the approach of the object.
When the observer or system changes the distance of the wave source, the frequency of the approaching wave will shift. This phenomenon is called the Doppler effect. Sonar and radar are made using the principle of this effect. Ultrasonic proximity switches, microwave proximity switches, etc. can be made using the Doppler effect. When there is an object approaching, the Doppler frequency shift is generated by the reflected signal received by the proximity switch, so that the presence or absence of the object can be identified.
Detects the stop, start, and passing positions of elevators and lifting equipment; detects the position of vehicles to prevent collision detection of two objects; detects the setting position of the working machine, moves the limit position of the machine or component; detects the stopping position of the rotating body, and the valve On or off position.
Metal plate punching size control device; automatic selection, identification of metal length; detection of automatic loading and unloading height; detection of the length, width, height and volume.
Check for the presence of objects. Check whether there is a product packaging box on the production packaging line; check for product parts.
Speed and speed control
Control the speed of the conveyor belt; control the rotational speed of the rotating machine; control the speed and the number of revolutions with various pulse generators.
Counting and Control
Detect the number of products flowing on the production line; measure the number of revolutions of a high-speed rotary shaft or disk; count parts.
Check the presence or absence of bottle caps; product qualification and non-conformity judgment; detect the lack of metal products in the packaging box; distinguish between metal and non-metal parts; whether the product has tag inspection; crane danger zone alarm; automatic start and stop of the escalator.
Automatic metering of products or parts; detection of meter or meter pointer range to control number or flow; detection of buoys to control surface height, flow; detection of iron buoys in stainless steel barrels; control of upper or lower meter range; flow control, level control.
The recognition is based on the code on the carrier.
ASI (Bus) connects the sensors in various positions on the equipment in the production line (50-100 meters) for data transmission back and forth.
Proximity switches have a wide range of applications in aerospace, aerospace technology and industrial production. In daily life, such as automatic doors for hotels, restaurants, and garages, there are applications on automatic hot air blowers. In terms of security and anti-theft, such as data files, accounting, finance, museums, treasury and other places, are usually equipped with anti-theft devices composed of a variety of proximity switches. In measurement technology, such as length, position measurement; in the control technology, such as displacement, velocity, acceleration measurement and control, also use a large number of proximity switches.
Eddy current proximity switches and capacitive proximity switches are commonly used in general industrial production sites. Because these two kinds of proximity switches require less environmental conditions.
When the object to be measured is a conductive object or an object that can be fixed on a metal object, an eddy current proximity switch is generally selected because of its high response frequency, good resistance to environmental interference, wide application range, and low price.
If the measured object is non-metal (or metal), liquid level, powder height, plastic, tobacco and so on. Capacitive proximity switches should be used. This switch has a low response frequency but good stability. The environmental factors should be considered when installing.
If the object to be measured is a magnetically permeable material or a magnetic steel is buried in the object to be measured in order to distinguish it from an object that moves with it, the Hall proximity switch should be selected, which has the lowest price.
In the case of better environmental conditions and no dust pollution, photoelectric proximity switches can be used. When the photoelectric proximity switch works, it has almost no effect on the measured object. Therefore, it is widely used in tobacco machinery in the demanding fax machines.
In anti-theft systems, automatic doors typically use pyroelectric proximity switches, ultrasonic proximity switches, and microwave proximity switches. Sometimes, in order to improve the reliability of recognition, the above-mentioned types of proximity switches are often used in combination.
No matter which kind of proximity switch is chosen, attention should be paid to the requirements for various indicators such as working voltage, load current, response frequency, and detection distance.