Proximity switches include inductive, capacitive, Hall, AC, DC. Proximity switch, also known as non-contact proximity switch, is the ideal electronic switch sensor.
(I) The main function
1. Detection distance
Detection of the elevator, lifting equipment stop, start, through the location; Detection of the vehicle’s location, to prevent collision detection of two objects; Detection of the setting position of the machine, moving the machine or part of the limit position; Rotary body to detect the stop position, the valve On or off position;
Check the cylinder or cylinder piston movement position.
2. Size control
Metal plate punching the size of the control device; automatic selection, identification of metal pieces of length; automatic loading and unloading height detection; detection of items of length, width, height and volume.
3. Detection of the presence of objects Whether the detection of production packaging line with or without product packaging; detection of product parts.
4 speed and speed control
Control the speed of the conveyor belt; control the speed of the rotating machinery; control the speed and revolutions together with various pulse generators.
5. Counting and control
Detection of the number of products flowing through the production line; high-speed rotary axis or disk rotation measurement; parts count.
6. Detection of abnormalities
Check whether the bottle cap; Product qualified and unqualified judgment; Detection of the lack of packaging products within the metal or not; Differentiation between metal and non-metallic parts; Products with or without signage detection; Crane danger zone alarm; Escalator automatically start and stop.
7. Metering control
Automatic measurement of products or parts; Detecting the range of indicators of meters and meters and controlling the number or flow rate; Detecting buoys controlling the height and flow of measuring surfaces; Detecting iron buoys in stainless steel barrels; Control of upper and lower instrument ranges; Flow control, control.
Identify the object
According to the code on the carrier identification is not.
9. Information transfer
ASI (bus) connection device on the location of the sensor in the production line (50-100 meters) in the data transfer and so on.
(Ii) classification and structure
The function of the proximity switch is to signal when an object approaches the proximity switch and reaches a certain distance. It does not require external force, is a non-contact type of master electrical appliances. Its use has gone far beyond the travel switch with stroke control and limit protection.
1. Proximity switch can be used for high-speed counting, detection of the presence of metal body, speed, level control, test parts size and as non-contact buttons. At present, the more widely used proximity switches can be classified into the following types according to the working principle:
(1) high-frequency oscillation type: used to detect a variety of metal body
(2) Capacitive type: used to detect a variety of conductive or non-conductive liquid or solid
(3) Photoelectric type: used to detect all opaque material
(4) ultrasonic type: used to detect the material that does not transmit ultrasound
(5) electromagnetic induction type: to detect magnetic or non-magnetic metal
2. According to the shape of the shape can be divided into cylindrical, square, ditch type, perforated (through) type and separation type. Cylindrical than the square to facilitate the installation, but its detection characteristics of the same, the groove-type test site is inside the groove, for detecting objects through the slot, through-type rarely produced in our country, while Japan is more commonly used, can be used Small parts such as screws or balls and buoys are assembled into water level detection devices.
3. Proximity switches can be divided according to the power supply; DC and AC type, according to the output type can be divided into two-wire DC system, DC three-wire system, DC four-wire system, AC two-wire system and AC three-wire system.
(1) two-wire proximity switch
Two-wire proximity switch installation is simple, convenient wiring; more widely used, but there are residual voltage and leakage shortcomings.
(2) DC three-wire
DC three-wire proximity switches have two kinds of NPN and PNP output, the vast majority of Japanese products in the 1970s is NPN output, NPN, PNP in both Western European countries have both output type. PNP output proximity switch generally used in PLC or computer as a control instruction more,
NPN output proximity switch for controlling more DC relays, in practice, according to the characteristics of the control circuit to choose the output form.
(Iii) selection and testing
1. Proximity switch selection
For different materials and different test body detection distance, should use different types of proximity switches to make it in the system with high cost performance, this selection should follow the following principles:
2. When the test body is a metal material, should use high-frequency oscillating proximity switches, the type of proximity switch on the iron-nickel, A3 steel test the most sensitive detection. For aluminum, brass and stainless steel test body, the detection sensitivity is low.
(1) Capacitive proximity switches should be used when the test specimen is a non-metallic material such as wood, paper, plastic, glass and water.
(2) metal body and nonmetal to remote detection and control, you should choose photoelectric proximity switch or ultrasonic proximity switch.
(3) For the detection of metal, if the detection sensitivity is not high, the choice of low-cost magnetic proximity switches or Hall-type proximity switches.
3. Proximity switch detection of technical indicators
(1) Determination of the movement distance. When the action piece is moved from the front to the induction surface of the proximity switch, the distance that the proximity switch moves is the maximum movement distance of the proximity switch. The measured data should be within the parameter range of the product.
(2) Determination of the release distance; when the action piece leaves the sensitive surface of the proximity switch from the front and the switch is changed from action to release, the maximum distance of the action piece from the sensing surface is measured.
(3) Determination of hysteresis H; the absolute value of the difference between the maximum operating distance and the release distance.
(4) Determination of the operating frequency; speed motor driven bakelite disc, a fixed number of steel on the disc, adjust the switch sensing surface and the distance between the action pieces, about the switch action distance of about 80%, turn the disc, Followed by the action piece close to the proximity switch,
In the spindle with a speed measuring device, the switch output signal shaping, connected to the digital frequency meter. Start the motor at this time, and gradually increase the speed, the speed and the action of the product and the frequency of counting equal conditions, the frequency meter can be directly read out the operating frequency of the switch.
(5) Repeatability determination; the action piece is fixed on the measuring tool, and the movement speed is controlled at 0.1mm / s from the front of the switch sensing surface except the 120% of the switch operating distance. When the switch action, read out the readings on the gauge, and then exit the action zone, the switch off. So repeat 10 times, the final calculation of 10 times the maximum and minimum measured value and 10 times the average of the difference, the greater the difference between the repeat accuracy error.