According to the different phenomena of photoelectric effect, photoelectric effect can be divided into three categories: external photoelectric effect, internal photoelectric effect and photovoltaic effect. Photoelectric devices include photocells, photomultiplier tubes, photoresistors, photoresistors, phototransistors, photocells, etc.
Generally speaking, photoelectric sensor consists of three parts, which are 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 (LEDs), 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.
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Application of photoelectric sensor
1, smoke turbidity monitor
In order to eliminate industrial smoke pollution, it is necessary to monitor the smoke source, display it automatically and give an alarm when it exceeds the standard. The turbidity of smoke in flue is detected by the change of light in the process of propagation in flue. If the flue turbidity increases, the light emitted by the light source is absorbed and refracted by the smoke particles, and the light reaching the photodetector decreases, so the output signal of the photodetector can reflect the change of flue turbidity.
2. Bar code 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.
3. Product counter
When the product runs on the conveyor belt, it constantly blocks the light path from the light source to the photoelectric sensor, so that the photoelectric pulse circuit produces one electrical pulse signal after another. Every time the product is shielded, the photoelectric sensor circuit generates a pulse signal, so the number of pulses output represents the number of products, which is counted by the counting circuit and displayed by the display circuit.
4, photoelectric smoke alarm
When there is no smoke, the light emitted by LED travels in a straight line, and the phototransistor can't receive the signal. When there is no output and 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, measuring speed
The rotating shaft of the motor is painted in black and white. When it rotates, reflected light and non-reflected light appear alternately. The photoelectric sensor correspondingly discontinuously receives the reflected signal of light, outputs intermittent electrical signals, and outputs square wave signals after being amplified and shaped by an amplifier and a shaping circuit. Finally, the electronic digital display outputs the rotating speed of the motor.
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