1. Smoke turbidity monitoring to prevent industrial smoke pollution is one of the important tasks of environmental protection. To eliminate industrial smoke pollution, we must first know the smoke emission, so we must monitor the smoke source, automatically display it and give an alarm if 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. Second, the bar code scanning pen When the scanning pen moves on the bar code, if it encounters a 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 a cut-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. Thirdly, when the product counter 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. When the photoelectric smoke detector is smokeless, the light emitted by the 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. Measure the rotating speed. Paint black and white on the rotating shaft of the motor. When rotating, 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. Application of intransitive verb photovoltaic cell in photoelectric detection and automatic control When photovoltaic cell is used as photoelectric detection, its basic principle is the same as that of photodiode, but their basic structure and manufacturing technology are not exactly the same. Because photovoltaic cells do not need external voltage when working; It has the advantages of high photoelectric conversion efficiency, wide spectral range, good frequency characteristics and low noise, and is widely used in photoelectric reading, photoelectric coupling, grating ranging, laser collimation, film playback, ultraviolet monitors and gas turbine flameout protection devices.