A proximity switch is a position switch that can be operated without direct mechanical contact with moving parts. When an object approaches the sensing surface of the switch to a certain distance, the switch can be activated without any mechanical contact or pressure, thereby driving DC electrical appliances or providing control instructions to computer (PLC) devices. A proximity switch is a switch type sensor (i.e. a contactless switch) that combines the characteristics of a travel switch and a micro switch, as well as sensing performance. It has reliable action, stable performance, fast frequency response, long application life, strong anti-interference ability, and is waterproof, shockproof, and corrosion-resistant. The products mainly include inductive, capacitive, Hall, AC, and DC types.

A proximity switch, also known as a contactless proximity switch, is an ideal electronic switch sensor. When the metal detector approaches the sensing area of the switch, the switch can quickly issue electrical commands without contact, pressure, or sparks, accurately reflecting the position and stroke of the moving mechanism. Even for general stroke control, its positioning accuracy, operating frequency, service life, ease of installation and adjustment, and adaptability to harsh environments cannot be compared to general mechanical stroke switches. It is widely used in industries such as machine tools, metallurgy, chemical engineering, textiles, and printing. In automatic control systems, it can be used as a limiting, counting, positioning control, and automatic protection link.

Performance characteristics

When an object moves towards the proximity switch and approaches a certain distance, the switch will activate. This distance is usually referred to as the 'detection distance'. But the detection distance of different proximity switches is also different.

Sometimes the object being tested is moved towards the proximity switch one by one at a certain time interval, and then left one by one, repeating this process continuously. Different proximity switches have different response capabilities to the detected object. This response characteristic is called "response frequency".

type

Passive proximity switch

This type of switch does not require a power supply, and its closed state is controlled by magnetic induction. When the magnetic or iron trigger approaches the switch magnetic field, it controls the closure by interacting with the internal magnetic force of the switch. Features: No need for power supply, non-contact, maintenance free, environmentally friendly.

Eddy current proximity switch (inductive proximity switch)

This type of switch is sometimes called an inductive proximity switch. It uses conductive objects to generate eddy currents inside the object when approaching the proximity switch that can generate an electromagnetic field. This eddy current reacts with the proximity switch, causing changes in the internal circuit parameters of the switch, thereby identifying the presence or absence of conductive objects moving closer and controlling the on or off of the switch. The object that this proximity switch can detect must be a conductive material.

1. Principle: The oscillator is composed of an inductor, a capacitor, and a transistor, and generates an alternating magnetic field. When a metal object approaches this magnetic field, eddy currents are generated inside the metal object, causing the oscillation to stop. This change is amplified by the back pole and converted into a transistor switch signal output.

2. Features: A. Good anti-interference performance, high switching frequency, greater than 200HZ B、 Can only sense metal

3. Applied to various mechanical equipment for position detection, counting signal picking, etc.

Capacitive proximity switch

The measurement of this type of switch usually involves one electrode of the capacitor, while the other electrode is the outer shell of the switch. This casing is usually grounded or connected to the device casing during the measurement process. When an object moves towards a proximity switch, regardless of whether it is a conductor or not, its proximity always causes a change in the dielectric constant of the capacitor, resulting in a change in capacitance and a change in the state of the circuit connected to the measuring head. This allows for the control of the switch's on or off state. The objects detected by this proximity switch are not limited to conductors, but can also be insulating liquids or powders.

Hall proximity switch

Hall element is a type of magnetic sensitive component. A switch made using Hall elements is called a Hall switch. When a magnetic object moves closer to the Hall switch, the Hall element on the switch detection surface generates the Hall effect, causing a change in the internal circuit state of the switch, thereby identifying the presence of a magnetic object nearby and controlling the on or off of the switch. The detection object of this proximity switch must be a magnetic object.

Photoelectric proximity switch

A switch made using the photoelectric effect is called a photoelectric switch. Install the light-emitting device and the optoelectronic device in the same detection head in a certain direction. When a reflective surface (the object being detected) approaches, the photoelectric device receives the reflected light and outputs a signal, thereby "sensing" that an object is approaching.

Other types

When the observer or system changes the distance to the wave source, the frequency of the approaching wave will shift, and this phenomenon is called the Doppler effect. Sonar and radar are made using the principle of this effect. Doppler effect can be used to create ultrasonic proximity switches, microwave proximity switches, etc. When an object approaches, the reflected signal received by the proximity switch will produce a Doppler frequency shift, which can identify whether an object is approaching.

major function

Inspection distance
Detect the stopping, starting, and passing positions of elevators and lifting equipment; Detecting the position of the vehicle to prevent collision detection between two objects; Detecting the set position of working machinery and the extreme position of moving machines or components; Detect the stopping position of the rotating body and the opening or closing position of the valve.

Size control
Size control device for metal plate punching and shearing; Automatically select and identify the length of metal parts; Detect the height of the stack during automatic loading and unloading; Detect the length, width, height, and volume of the item< br /> Check for the presence of objects and whether there are product packaging boxes on the production packaging line; Check for the presence of product parts< br /> Speed and Speed Control
Control the speed of the conveyor belt; Control the rotational speed of rotating machinery; Control the speed and rotation speed together with various pulse generators< br /> Counting and Control
Detect the number of products flowing through the production line; Measurement of the number of revolutions of high-speed rotating shafts or disks; Counting of components< br /> Detecting anomalies
Check for bottle caps; Product qualification and nonconformity assessment; Check whether there is a lack of metal products inside the packaging box; Distinguish between metal and non-metal parts; Whether the product has label detection; Crane danger zone alarm; The safety escalator automatically starts and stops.

Measurement control
Automatic measurement of products or parts; Detecting the pointer range of measuring instruments and meters to control numbers or flow rates; Detecting buoy to control the height and flow rate of the measuring surface; Detecting iron buoys in stainless steel barrels; Control of the upper or lower limit of the instrument range; Flow control, horizontal control< br /> Identify objects
Identify right from wrong based on the code on the carrier< br /> Information transmission
ASI (bus) connects sensors at various locations on the device to transmit data back and forth in the production line (50-100 meters).

structural style

Proximity switches can be divided into cylindrical, square, groove, perforated (through), and separated types according to their external shapes. The cylindrical type is easy to install, but its detection characteristics are the same. The detection part of the groove type is on the inside of the groove, used to detect objects passing through the groove. The through type is rarely produced in China, while it is more commonly used in Japan and can be used for assembling small parts such as screws or balls and buoys into water level detection devices.

Connection method of proximity switch

1) There is a difference between two-wire and three wire proximity switches. Three wire proximity switches are divided into NPN and PNP types, and their wiring is different.

2) The wiring of the two-wire proximity switch is relatively simple. The proximity switch can be connected in series with the load and then connected to the power supply.

3) The wiring of the three wire proximity switch: the brown (red) wire is connected to the positive end of the power supply; Connect the blue wire to the 0V end of the power supply; The black (yellow) line is the signal and should be connected to the load. The other end of the load is connected as follows: for NPN type proximity switches, it should be connected to the positive terminal of the power supply; For PNP type proximity switches, they should be connected to the 0V terminal of the power supply.

4) The load of the proximity switch can be a relay coil or a digital input module of a programmable logic controller (PLC).

5) Special attention should be paid to the type selection of the three wire proximity switch connected to the PLC digital input module. PLC digital input modules can generally be divided into two types: one type has a common input terminal of power supply 0V (the black line output is a negative signal, i.e. 0V), and current flows out from the input module (Japanese mode). At this time, NPN type proximity switches must be selected; Another type of common input terminal is the positive terminal of the power supply (the black line output is a positive signal equivalent to the input power supply voltage), and the current flows into the input module, which is a trap type input (European mode). At this time, it is necessary to use a PNP type proximity switch. Don't choose the wrong one.

6) The two-wire proximity switch is limited by working conditions. When it is turned on, the switch itself generates a certain voltage drop, and when it is turned off, there is a certain residual current flowing through it. Therefore, it should be considered when selecting it. Although the three wire proximity switch has an additional wire, it is not affected by adverse factors such as residual current and works more reliably.

7) Some manufacturers will simultaneously output the "normally open" and "normally closed" signals of the proximity switch, or add other functions. In this case, please follow the product manual for specific wiring.

Slot type photoelectric switch wiring

The diode of the photoelectric switch is a light-emitting diode, and the output is a phototransistor. C is the collector and E is the emitter.

When a transistor is used as a switch, the collector is usually used as the output terminal.

General connection: The diode is the input terminal, E is grounded, C is connected to the load, and the other end of the load needs to be connected to a positive power supply. This method has a wide range of applications.

Special connection method: The diode is the input terminal, C is connected to the positive power supply, E is connected to the load, and the other end of the load needs to be grounded. This connection method is only applicable when the equivalent resistance of the load is very small (within a few tens of ohms). If the equivalent resistance of the load is relatively large, it may cause the working point of the switch transistor to be abnormal, resulting in unreliable switch operation.

Main purpose

Proximity switches are widely used in aviation, aerospace technology, and industrial production. In daily life, automatic doors and hot air fans are used in hotels, restaurants, and garages. In terms of security and theft prevention, important places such as archives, finance, accounting, museums, and vaults are usually equipped with anti-theft devices composed of various proximity switches. In measurement techniques, such as measuring length and position; In control technology, a large number of proximity switches are also used for measuring and controlling displacement, velocity, and acceleration.

Switch parameters

As shown in the figure

Sensor Body Material	A. B. S/brass nickel plating
Filling/Filler	epoxy resin
Max Contact Rating/Maximum Power	10W
Max Switching Voltage	36VDC/250VAC
Max Switching Current	0.5A
Min Breakdown Voltage	220 VDC
Max Carry Current/Maximum Load Current	1.0A
Max Contact Resistance/Maximum Corrosion Resistance	100 mΩ
Min Insulation Resistance	108 Ω
Release Time/Touching Time	0.1 ms Max
Operate Time/Release Time	0.4 ms Max

matters needing attention

In general industrial production sites, eddy current proximity switches (inductive proximity switches) and capacitive proximity switches are usually used. Because these two types of proximity switches have lower environmental requirements.

When the tested object is a conductive object or an object that can be fixed on a metal object, eddy current proximity switches (inductive proximity switches) are generally selected because of their high response frequency, good resistance to environmental interference, wide application range, and low price.

If the measured object is non-metallic (or metallic), liquid level height, powder height, plastic, tobacco, etc. A capacitive proximity switch should be selected. This type of switch has a low response frequency but good stability. Environmental factors should be considered during installation.

If the measured object is a magnetic material or a magnetic steel is buried inside the measured object to distinguish it from other objects moving together, a Hall proximity switch should be used.

In environments with good environmental conditions and no dust pollution, photoelectric proximity switches can be used. The photoelectric proximity switch has almost no impact on the measured object during operation. Therefore, it is widely used in tobacco machinery on high demand fax machines.

In anti-theft systems, automatic doors usually use pyroelectric proximity switches, ultrasonic proximity switches, and microwave proximity switches. Sometimes, in order to improve the reliability of recognition, the above-mentioned proximity switches are often used in combination.

Regardless of which proximity switch is selected, attention should be paid to the requirements for various indicators such as operating voltage, load current, response frequency, and detection distance.

Selection testing

model selection

For different materials and detection distances, different types of proximity switches should be selected to achieve high cost-effectiveness in the system. Therefore, the following principles should be followed in the selection process:

1.1. When the detection object is a metal material, a high-frequency oscillation type proximity switch should be selected, which is the most sensitive for detecting iron nickel and A3 steel detection objects.

The detection sensitivity of aluminum, brass, and stainless steel specimens is low.

1.2. When the test object is a non-metallic material, such as:; Capacitive proximity switches should be used for materials such as wood, paper, plastic, glass, and water.

1.3. When conducting remote detection and control of metal and non-metal objects, photoelectric proximity switches or ultrasonic proximity switches should be selected.

1.4. When the detection object is metal, if the detection sensitivity requirement is not high, magnetic proximity switches or Hall type proximity switches can be used.

testing

2.1. Measurement of action distance; When the action piece approaches the sensing surface of the proximity switch from the front, the distance of the proximity switch action should be the maximum action distance of the proximity switch, and the measured data should be within the parameter range of the product.

2.2. Determination of release distance; When the action piece moves away from the sensing surface of the proximity switch from the front and the switch switches from action to release, measure the maximum distance that the action piece moves away from the sensing surface.

2.3. Determination of hysteresis H; The absolute value of the difference between the maximum action distance and the release distance.

2.4. Determination of action frequency; Use a speed regulating motor to drive a rubberwood disc, fix several steel plates on the disc, adjust the distance between the switch sensing surface and the action plate to about 80% of the switch action distance, rotate the disc in sequence to bring the action plate closer to the proximity switch, and install a speed measuring device on the disc spindle. The switch output signal is shaped and connected to a digital frequency meter. At this point, start the motor and gradually increase the speed. Under the condition that the product of the speed and the action piece is equal to the frequency count, the frequency meter can directly read the action frequency of the switch.

2.5. Determination of repeatability accuracy; Fix the action piece on the measuring tool, and control the movement speed at 0.1mm/s from the front of the switch sensing surface near the action area of the switch, beyond 120% of the switch action distance. When the switch is activated, read the reading on the measuring tool and then exit the action area to disconnect the switch. Repeat this process 10 times, and finally calculate the difference between the maximum and minimum values of the 10 measurements and the average of the 10 measurements. The larger difference is the repeatability error.

Common models

Introduction to the proximity switch of Hugong Group

1、 LJ12A3-4-Z/BX (the most widely used) Model meaning: LJ -- represents the code of the inductive proximity switch of Shanghai Engineering Group, 12-- represents the external dimensions (product diameter: 8.12.18.30, etc.), A3-- represents the structural form (A3: cylindrical screw metal shell, A4: cylindrical screw plastic shell), 4-- represents the action distance (1:1mm, 2:2mm, 4:4mm, 5:5mm, etc.), Z -- represents the working voltage range (J: 90-250VAC, Z: 6-36VDC), B -- output form (A: three wire normally closed, B: three wire normally open, C: four wire normally open and closed, D: two wire normally closed, E: 2-wire normally open) X - output current (X: PNN  300mA, Y：PNP  300mA，Z：400mA)

2、 SN04-N, SN04-P (most widely used); Model meaning: SN - represents the square shape of Shanghai Industrial Group, 04- represents the sensing distance of 4mm, N - represents the output of NPN type, P - represents the output of PNP type, D - represents the output of DC two-wire system, Y - represents the output of AC two-wire system. None: normally open, 2: normally closed.

3、 TL-Q5MC1, TL-Q5MB1 (most widely used). Model meaning: TL - represents the square shape of Shanghai Industrial Group, 5- represents the sensing distance of 5mm, C - represents the output of NPN type, B - represents the output of PNP type, D - represents the output of DC two-wire system, Y - represents the output of AC two-wire system. 1: Normally open, 2: Normally closed.

4、 PL-05N, PL-05P (most widely used). Model meaning: PL - represents the square shape of Shanghai Engineering Group, 05- represents the sensing distance of 5mm, N - represents the output of NPN type, P - represents the output of PNP type, D - represents the output of DC two-wire system, Y - represents the output of AC two-wire system. None: normally open, 2: normally closed.

5、 LJC18A3-B-Z/BX (the most widely used) Model meaning: LJ - represents the code for the capacitive proximity switch of Shanghai Engineering Group, 18- represents the external dimensions (product diameter: 8.12.18.30, etc.), A3- represents the structural form (A3: cylindrical screw metal shell, A4: cylindrical screw plastic shell), 4- represents the operating distance (B: 1-10mm, T: 1-15mm, H: 1-20mm, K: 1-25mm), Z - represents the working voltage range (J: 90-250VAC, Z: 6-36VDC), B - represents the output form (A: three wire normally closed, B: three wire normally open, C: four wire normally open and normally closed, D: 2-wire normally closed, E: 2-wire normally open) X - output current (X: NPC  300mA, Y：PNP  300mA，Z：400mA)。

6、 E3F-DS10C4 (most widely used) Model meaning: E3F - Shanghai Industrial Group Appearance number (E3F: 18mm diameter cylindrical screw tube, E3F1: 12mm diameter cylindrical screw tube, E3F3: 30mm diameter cylindrical screw tube, E3JK: 50X50X18 square shell, E3JM: 25X60X75 square shell, E3S: 20X20X65 square shell), D - Detection method (D: diffuse reflection, R: feedback reflection, no: opposite, G: groove type), S: Detection distance (S: centimeter CM, no: meter M) 10- Detection distance (10:10, 30:30, 5:5) C - Output form (N.C.E: PNN) Type, P: PNP type, Y: AC two-wire system, M: relay contact with one open and one closed output), 4- output status (4 (1): normally open, 2: normally closed, 3 (12): one open and one closed).

7、 TCA-3020A (most widely used); Model meaning: TCA - Shanghai Engineering Group appearance number (TCA: 100X50X100, TCB: 140X55X140, TCC: 210X63X210, TCO: 80X40X80, SE: ф 55X35, SD: ф 48X32, SR: ф 42X24, SK: ф 36X18, SC: ф 40X20+M24X55, SM: ф 48X22+M24X55), 30- power supply voltage (20: AC90-250V, 30: DC6-36V), 20- action distance (15:15MM, 20:20MM, 50:50MM, etc.), A - output mode (A: DC is NPN triple) Line normally open, AC is AC two-wire normally open, B: DC is NPN three wire normally closed, AC is AC two-wire normally closed, C: PNP three wire normally open, D: PNP three wire normally closed, AL: DC two-wire normally open, BL: DC two-wire normally closed).

7、 NJK-5002C (most widely used); Model meaning: NJK - Hall sensor code of Shanghai Engineering Group, 50- External dimensions (50:25MM long, 80:35MM long, 90:50MM long), 02- External volume (01: 8mm diameter cylindrical screw tube, 02: 12mm diameter cylindrical screw tube, 03: 18mm diameter cylindrical screw tube, 010: 10mm diameter cylindrical screw tube), C - Output mode (C (none): NPN normally open, D: NPN normally closed,

A: PNP normally open, B: PNP normally closed.

8、 PR12-4DN (most widely used) Model meaning: P - Inductive proximity switch of Hugong Group, R - External dimensions (R: cylindrical screw tube, S: corner column type), 12- External dimensions (product diameter: 8.12.18.30, etc.), 4- Action distance (1:1mm, 2:2mm, 4:4mm, 5:5mm, etc.), DN - Output mode (DN: PN3 normally open, DP: PNP 3 normally open, DO: DC 2 normally open, DC 2 normally closed, AO: AC 2 normally open, AC 2 normally closed). None: normally open, 2: normally closed.

The above lists several common model descriptions. For other parameter models, please feel free to call for consultation. Sales hotline: 0577-6222222 & nbsp;62777008     Fax: 0577-62755058& nbsp; Company Address: No. 258 Liule Road, Liushi Town, Yueqing City, Zhejiang Province& nbsp; Store address: No. 41 Changxing Road, Liushi Town, Yueqing City, Zhejiang Province& nbsp; Sales Department Phone: 0577-62716881; Fax: 0577-62778800

Wiring instructions

The three wires of the DC three wire proximity switch are: brown wire - positive blue wire of the power supply - negative black wire of the power supply - output signal

2. AC two-wire switch: Connect the load and proximity switch in series to the AC power supply terminal, and the AC power supply is not divided into positive and negative poles.

3. DC two-wire switch: Connect the load and proximity switch in series to the AC power supply terminal, NPN and PNP are compatible.