The photoelectric sensor is controlled by converting the change of light intensity into the change of electric signal. Generally, it consists of transmitter, receiver and detection circuit. The transmitter aims at the target to emit light beams, which generally come from semiconductor light sources, light emitting diodes, laser diodes and infrared emitting diodes. Continuously emit light beams or change the pulse width. The receiver consists of photodiode, phototransistor and photocell. In front of the receiver, optical elements such as lens and aperture are installed. Behind it is a detection circuit, which can filter out effective signals and apply them.
2. What kinds of photoelectric sensors are there?
1. photoelectric sensors are divided into cylindrical and square according to the shell type.
At present, the shell of photoelectric sensor is round or square according to the installation environment of customers, and no regulations are made.
2. Photoelectric sensors are divided into retro-reflection, specular reflection and diffuse reflection according to detection methods.
The opposite photoelectric sensor has the farthest detection distance among photoelectric sensors, which can reach several meters or even more than ten meters. The device must have an optical transmitter and receiver facing each other.
The detection distance of specular photoelectric sensor is slightly shorter than that of incident sensor, but it is much more convenient to install. It can be installed in a narrow space. As long as a reflector is installed, it is characterized by professional detection of transparent objects.
The detection distance of diffuse reflection photoelectric sensor is not as good as the above two, but the installation mode and position of diffuse reflection photoelectric sensor are more convenient than the first two.
3. Photoelectric sensors are classified according to light sources: visible red light, invisible infrared light and laser.
The light source of photoelectric sensor is selected according to customer's requirements, detection object and detection environment. Visible red light and invisible red light will change the spot size with distance, but laser will not. The laser will not change the spot size because of the distance. Laser is suitable for detecting the existence, counting and positioning of small objects or tiny objects.
Third, the practical application of photoelectric sensor
Photoelectric sensors can be used to detect non-electric quantities that directly cause light quantity changes, such as light intensity, illumination, radiation temperature measurement, gas composition analysis and so on. It can also be used to detect other non-electric quantities that can be converted into light quantity changes, such as part diameter, surface roughness, strain, displacement, vibration, speed and acceleration, and to identify the shape and working state of objects.
1, barcode scanner
When the scanning pen moves on the bar code, if it meets the black line, the light of the LED will be absorbed by the black line, and the phototransistor will not receive the reflected light, showing high resistance and being in the off state. When a blank is encountered, the light emitted by the light emitting diode is reflected to the base of the phototransistor, and the phototransistor generates photocurrent to conduct. After the whole bar code is scanned, the phototransistor distorts the bar code into an electric pulse signal, which is amplified and shaped to form a pulse sequence, and then processed by the computer to complete the identification of bar code information.
2. Simple photosensitive alarm
When there is no light, the silicon photovoltaic cell has no voltage. At this time, the silicon photovoltaic cell is equivalent to a resistor connected in series with the base circuit of the amplifier. When there is light, the silicon photovoltaic cell generates voltage, which is added to the base of the VT 1 transistor together with the voltage on R2, so that VT 1 is turned on, VT2 and VT3 are also turned on, the relay K works, its contacts are attracted, and the buzzer sounds an alarm.
3, product count
When the product runs on the conveyor belt, it constantly blocks the light path from the light source to the photosensitive device, so that the photoelectric pulse circuit generates an electric pulse signal with the presence or absence of the product. Every time a product is blocked, the photoelectric pulse circuit generates a pulse signal, so the number of pulses output represents the number of products. The pulses are counted by the counting circuit and displayed by the display circuit.
4, photoelectric smoke alarm
When there is no smoke, the light emitted by the light emitting diode propagates in a straight line, and the phototransistor does not receive signals and outputs; When there is smoke, the light emitted by the LED is refracted by the smoke particles, so that the triode receives the light, outputs a signal and gives an alarm.
5, anti-theft alarm circuit
Install a photoelectric circuit breaker behind the drawer, and set a power switch in a hidden place. When anti-theft is needed, turn off the switch. Usually, because the baffle is inserted into the notch, the phototransistor has only dark current, BG is not conductive, and relay J is not attracted. When the thief pried open the drawer, the baffle left the gap as soon as the drawer was opened. The photocurrent of the phototransistor makes R2 generate a voltage close to the power supply, BG turns on, and the relay is attracted to send out an alarm signal.
6, male * * door safety indicator light
When the door is closed, the baffle is inserted into the notch of the photoelectric circuit breaker, and the phototransistor has no working current, and its output is high level; When the three doors are fully closed, three high-level signals are output accordingly. Then the AND gate output is high, and the green light is on. If one of the doors is not properly closed (or closed), the AND gate output is low and the red light is on.