The photoelectric switch is a member of a large family of sensors, which converts the strong and weak light between the transmitting end and the receiving end into a change of current in order to achieve the purpose of detection. Since the photoelectric switch output circuit and the input circuit are electrically isolated (ie, electrical margin), it can be used in many applications.
Second, photoelectric switch
1, working principle
Photoelectric switch (photoelectric sensor) is the abbreviation of photoelectric proximity switch. It uses the object to block or reflect the light beam and strobes the circuit by the synchronous circuit to detect the presence or absence of an object. Objects are not limited to metal, and all objects that reflect light can be detected. The photoelectric switch converts the input current into an optical signal on the transmitter, and the receiver then detects the target object according to the received light intensity or presence or absence. The working principle is shown in Figure 1. Most photoelectric switches use infrared light wavelengths that are close to visible light. Figure 2 is a partial appearance of the photoelectric switch of the SICK company in Germany.
2, photoelectric switch classification and terminology
(1) Classification
1 Diffuse-reflective photoelectric switch: It is a sensor that integrates a transmitter and a receiver. When there is an object to be detected, the object reflects a sufficient amount of light emitted by the photoelectric switch transmitter to the receiver, so the photoelectric switch The switch signal is generated. When the surface of the object to be inspected is bright or its light reflectance is extremely high, a diffuse reflection photoelectric switch is the preferred detection mode.
2 mirror-reflective photoelectric switch: It also integrates the transmitter and receiver in one, the light emitted by the photoelectric switch reflector reflected back to the receiver through the mirror, when the object is detected and completely blocked light, the photoelectric switch has been generated Detect switch signal.
3 Optoelectronic photoelectric switch: It includes transmitters and receivers that are separated from each other in structure and placed opposite to each other in the optical axis. The light from the transmitter enters the receiver directly, when the detected object passes between the transmitter and the receiver. When the light is blocked, the photoelectric switch produces a switching signal. When the object is opaque, the photoelectric switch is the most reliable detection device.
Four-slot photoelectric switch: It usually adopts a standard U-shaped structure. Its transmitter and receiver are located on both sides of the U-shaped groove respectively, and form an optical axis. When the detected object passes through the U-shaped groove and blocks the optical axis. , The photoelectric switch produces a switch signal. Trough photoelectric switch is more suitable for detecting high-speed moving objects, and it can distinguish between transparent and semi-transparent objects, and it is safe to use.
5 fiber optic switch: It uses a plastic or glass fiber optic sensor to guide the light, can detect objects far away. Optical fiber sensors are generally divided into two types: radiation and diffuse reflection.
A schematic diagram of their working light is shown in Figure 3.
(2) Explanation of Terms
The common terminology diagram is shown in Figure 4.
1 detection distance: refers to the detection body moves in a certain way, when the switch action measured at the reference position (sensor switch sensing surface) to the detection surface of the spatial distance. The nominal operating distance is the nominal value of the proximity switching distance.
2 Return distance: The absolute value between the action distance and the reset distance.
3 Response frequency: The number of allowable photoelectric switch cycles during the specified 1s time interval.
4 output state: points normally open and normally closed. When no object is detected, the load connected to the normally open photoelectric switch does not work due to the cutoff of the output transistor inside the photoelectric switch. When an object is detected, the transistor is turned on and the load is powered.
5 Detection method: According to the different ways in which the light emitted by the transmitter when the photoelectric switch detects the object is returned to the receiver, it can be classified into a diffuse reflection type, a mirror reflection type, and a radiation type.
6 output form: divides NPN two lines, NPN three lines, NPN four lines, PNP two lines, PNP three lines, PNP four lines, AC two lines, AC five lines (with relays), and DC NPN/PNP / normally open / normally closed function Wait for several common output forms.
7 Pointing angle: See the schematic diagram of the pointing angle of the photoelectric switch, as shown in the lower three thumbnails in Figure 4.
8 Surface Reflectivity: The light emitted by a diffuse photoelectric switch needs to pass through the surface of the object to be reflected back to the receptor of the diffuse switch. Therefore, the detection distance and the surface reflectivity of the object to be detected will determine the intensity of the light received by the receiver. The intensity of the light reflected back from the rough surface must be less than the intensity of the reflection from the smooth surface, and the surface of the object to be inspected must be perpendicular to the emitted light of the photoelectric switch. The reflectance of commonly used materials is shown in Table 1.
Table 1 Reflectance of commonly used materials
Material Reflectance Material Reflectance
White drawing paper 90% opaque black plastic 14%
Newspapers 55% Black Rubber 4%
Napkin 47% Black Fabric 3%
Box cardboard 68% Unpolished white metal surface 130%
Clean Pine 70% Gloss Light Metal Surface 150%
Clean rough board 20% stainless steel 200%
Transparent plastic cup 40% Cork 35%
Translucent plastic bottle 62% beer foam 70%
Opaque white plastic 87% palm of person 75%
9 Environmental characteristics: The environment in which photoelectric switches are applied will also affect their long-term workability. When the photoelectric switch is operated at the maximum detection distance, the optical lens may be corroded by dirt in the environment and even be corroded by some strong acidic substances, so that its use parameters and reliability are reduced. The simpler solution is to determine the optimal working distance based on the maximum detection distance (Sn) derating of the photoelectric switch.
(3) Precautions for use
1 The infrared sensor is a diffuse reflection type product. The standard sample used is a flat white drawing paper.
2 Infrared photoelectric switch can work stably under high ambient illumination conditions, but in principle it should be avoided that the optical axis of the sensor is facing the strong light source such as sunlight.
The minimum detectable width of the 3-beam photoelectric switch is 80% of the width of the photoelectric switch lens.
4 When inductive loads (such as lamps, motors, etc.) are used, their transient inrush current is large, which may degrade or damage the AC two-wire photoelectric switch. In this case, change the load through the AC relay.
5 The lens of the infrared photoelectric switch can be wiped with a lens paper, and chemicals such as dilute solvent are prohibited so as not to permanently damage the plastic mirror.
6 In view of the user's actual site requirements, in some of the more severe conditions, such as dusty occasions, the production of photoelectric switches in the sensitivity of the choice of an increase of 50%, in order to adapt to long-term use of extended photoelectric switch maintenance cycle Claim.
7 products are manufactured by SMD process, and are manufactured after passing strict test. No damage will occur under normal circumstances. In order to avoid accidents, please check whether the wiring is correct and check whether the voltage is rated before turning on the power.
The schematic diagram of the above precautions is shown in Figure 5.
Third, application examples
From Fig. 6, various applications of photoelectric switches can be seen. Among them, Fig. 6 (a) is a photoelectric switch used for the positioning shear control of the material; Fig. 6 (b) is a photoelectric switch to control the upper and lower limits of the liquid level, when the liquid level is above or below the upper and lower limits When the liquid level, the photoelectric switch control circuit can make the threshold door open or closed, so that the height of the liquid surface is maintained between the upper and lower limits; Figure 6 (c) is the use of objects to block the light, the number of objects through the detection Whether or not objects exist; Figure 6(d) uses the linear propagation of light to check if the products are arranged at equal heights; Figure 6(e) shows the number of products that are to be tested by using optoelectronic switches on a production line; Figure 6 (f) To detect the level of the liquid level using a photoelectric switch.