Proximity switch
The proximity switch is a position switch that can be operated without direct mechanical contact with the moving parts. When the object is close to the sensing surface of the switch to the operating distance, the switch can be actuated without the need for mechanical contact and any pressure to drive the DC motor Or to provide control instructions to a computer (plc) device. The proximity switch is a kind of switch type sensor (that is, no contact switch), it has both trip switch, micro switch characteristics, but also has sensor performance, and reliable, stable performance, fast frequency response, long life, anti-interference Strong ability, and has a waterproof, shock, corrosion and other characteristics. Products are inductive, capacitive, Hall type, pay, DC type. Proximity switches, also known as non-contact proximity switches, are ideal for electronic switch sensors. When the metal detector close to the sensor sensor area, the switch can be no contact, no pressure, no spark, quickly issued electrical instructions, accurately reflect the movement of the body position and travel, even for general stroke control, positioning accuracy, operation Frequency, service life, ease of installation and the ability to adapt to harsh environments, is the general mechanical travel switch can not be compared. 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.

Performance characteristics
In the various types of switches, there is a component close to its object “perceived” ability – displacement sensor. The use of displacement sensors on the proximity of the object to achieve the purpose of the control switch on or off the purpose, which is close to the switch.
When the object moves closer to the switch, and close to a certain distance, the displacement sensor only “perception”, the switch will move. Usually this distance is called “detection distance”. But the distance between the different proximity switches is also different.
Sometimes the test object is detected at a certain time interval, one by one to move closer to the switch, and one by one to leave, so continue to repeat. Different proximity switches, the ability to respond to the detection object is different. This response characteristic is called the “response frequency”.

Because the displacement sensor can be made according to different principles and different methods, and not inductive proximity switch with the displacement sensor on the object “perception” method is also different, so the common proximity switch has the following:
Passive Proximity Switches This switch does not require a power supply and controls the closed state of the switch by magnetic induction. When the magnetic or iron trigger near the switch magnetic field, and the switch internal magnetic force control closed. Features: no power, non-contact, maintenance-free, environmentally friendly.

Eddy current proximity switch
This switch is sometimes called an inductive proximity switch. It is the use of conductive objects close to this can produce electromagnetic field close to the switch, so that the object inside the eddy current. This vortex reaction to the proximity switch, so that the switch internal circuit parameters change, thus identifying the presence or absence of conductive objects closer, and then control the switch on or off. The object that can be detected by this proximity switch must be an electrical conductor.
1. Principle: The inductor coil and the capacitor and the transistor form the oscillator, and produce an alternating magnetic field, when there is a metal object close to the magnetic field will be generated in the metal object eddy current, which led to oscillation stop, this change is Polarization is converted to transistor switching signal output.
2. Features: A, anti-jamming performance, high switching frequency, greater than 200HZ. B, only induction metal
3. Application in a variety of mechanical equipment for location detection, counting signal picking and so on.

Capacitive proximity switches
The measurement of this switch is usually one of the plates forming the capacitor, and the other is the housing of the switch. The housing is usually grounded or connected to the housing of the device during the measurement. When an object moves toward the proximity switch, whether or not it is a conductor, the dielectric constant of the capacitor changes due to its proximity, causing the capacitance to change so that the circuit state associated with the probe Change, which can control the switch on or off. Such proximity switches are not limited to conductors, insulating liquids or powders, and the like.

Hall proximity switch
Hall element is a magnetic element. A switch made of a Hall element, called a Hall switch. When the magnetic object is moved closer to the Hall switch, the Hall element on the switch detection surface changes the state of the internal circuit of the switch due to the Hall effect, thus recognizing the presence of a magnetic object in the vicinity and controlling the opening and closing of the switch. The object of this proximity switch must be a magnetic object.

Photoelectric proximity switch
The use of photoelectric effect made of the switch called photoelectric switch. The light-emitting devices and optoelectronic devices in a certain direction in the same detection head. When there is a reflective surface (detected object) close to the photoelectric device to receive the reflected light in the signal output, which can “perceive” an object close.

Other types
When the observer or system changes the distance to the wave source, the frequency of the near-wave will shift, a phenomenon known as the Doppler effect. Sonar and radar are made using the principle of this effect. The use of Doppler effect can be made of ultrasonic proximity switches, microwave proximity switches and so on. When there is an object closer, the proximity signal received by the proximity switch will produce Doppler shift, which can identify whether the object close.

The main function
Detecting the position of the moving machine or the limit position of the moving machine or the parts; detecting the stop position of the rotating body, detecting the position of the moving machine, detecting the position of the moving machine, The opening or closing position of the valve.

Size control
Metal plate punching the size of the control device; automatic selection, identification of metal parts length; detection of automatic loading and unloading heap height; detection of items long, wide, high and volume. Detection of the existence of the presence of the product Whether there is no product packaging on the packaging line; to detect the presence of product parts. Speed ​​and speed control to control the speed of the conveyor; control the speed of rotating machinery; with a variety of pulse generator control speed and speed.
The following are the same as the ”
Counting and control
Detection of the number of products flowing through the production line; high-speed rotation of the axis or disk rotation measurement; parts count. Detection of anomalies
Detection of the cap with or without; product qualified and failed to judge; detection of metal products within the box lack or not; distinguish between metal and non-metallic parts; product with or without signs testing; crane dangerous area alarm; safety escalator automatically start and stop.
The following are the same as the ”
Metering control
Product or parts of the automatic measurement; detection meter, the instrument pointer range and control the number or flow; detection buoy control surface height, flow; detection of stainless steel bucket iron buoy; instrument range upper or lower limit control; flow control, control.

Identify the object
According to the code on the carrier identification is right and wrong. Information Transfer The ASI (bus) connects the sensors on each location on the device in the production line (50-100 meters) for data transfer.

structure type
The proximity switch can be divided into cylindrical type, square type, groove type, perforated (through type) and separated type according to its shape. The cylindrical type is easy to install, but its detection characteristics are the same. The detection area of ​​the groove type is inside the groove, which is used to detect the objects passing through the tank. The through type is rarely produced in our country, while Japan is widely used and can be used Small screws or ball like small parts and buoys assembled into a water level detection device.

Proximity switch wiring diagram
1) proximity switch has two lines and three lines of the difference, three-wire proximity switch is divided into NPN and PNP type, their wiring is different. See below:
2) two-wire proximity switch wiring is relatively simple, close to the switch and load connected to the power can be connected.
3) 3-wire proximity switch wiring: red (brown) line power supply positive side; blue line connected to power 0V side; yellow (black) line for the signal, should load. The other end of the load is connected to this: for NPN proximity switches, should be connected to the positive power supply; for PNP type proximity switch, you should receive the power 0V side.
4) The load of the proximity switch can be a digital input module for a semaphore, a relay coil, or a programmable controller PLC.
5) Need special attention to the PLC digital input module received three-wire proximity switch type selection. PLC digital input module can be divided into two categories: a class of common input for the power positive, the current flow from the input module, this time, we must use NPN proximity switch; another type of common input for the power supply negative, Current into the input module, this time, we must use PNP type proximity switch. Do not choose the wrong.
6) two-wire proximity switch by the working conditions of the restrictions, turn on the switch itself to produce a certain pressure drop, cut off when there is a certain residual current flow, the selection should be considered. Although the three-wire proximity switch is more than a line, but not the residual current and other unfavorable factors, work more reliable.
7) Some manufacturers will be close to the switch “normally open” and “normally closed” signal at the same time leads, or add other features, this situation, please follow the product manual specific wiring.

Grooved photoelectric switch wiring
Photoelectric switch that diode is a light-emitting diode, the output is the photosensitive transistor, C is the collector, E is the emitter. General triode for switch use, usually with the collector as the output.
General connection: diode for the input, E ground, C load, the other end of the load need to connect the positive power supply. This method of application is relatively wide range.

Special connection: the diode for the input, C then the power supply is positive, E load, the other end of the load need to ground. This connection is only applicable when the load equivalent resistance is very small (tens of ohms or less), if the load equivalent resistance is relatively large, may cause the switch transistor operating point is not normal, resulting in unreliable switch work.

The main purpose
The proximity switches are widely used in aviation, aerospace, and industrial production. In daily life, such as hotels, restaurants, garage automatic doors, automatic hot air fans have applications. In the area of ​​security and security, such as data files, accounting, finance, museums, treasuries and other heavy places, usually equipped with a variety of proximity switch composed of anti-theft device. In the measurement technology, such as length, position measurement; in the control technology, such as displacement, speed, acceleration measurement and control, also use a large number of proximity switches.

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