This smoke detector can to register or smoke a high concentration of opaque dust particles suspended in the air, the Device can be used in hot shops (foundry, welding), cement factories, sawmills, garages and in closed stands. The device will alert you to high concentrations of smoke, harmful dust suspensions and will automatically turn on the ventilation system. The device can be set to a higher output and post the tube sensor smoke on great distance and, conversely, at high sensitivity.
Diagram of the device shown in the figure. The smoke detector consists of светодиодаVD1 and photodiode VD2 operating in the infrared region of the spectrum. The light from the led type AL passes through the gap between the tube and illuminates the photodiode VD2 type FD. Photodiode open, and the cathode produces positive voltage, which is is supplied to the inverting input of the operational amplifier DA1. To the second input amplifier with the output of the variable resistor R4 receives the reference voltage That resistor to set the sensitivity. In the absence of air or smoke dust the voltage at the cathode of the photodiode VD2 exceeds the voltage, remove from engine the variable resistor R4, the output of the operational amplifier DA1 the voltage is close to zero. When this led VD3 is not lit, and the element DD1.1. locked.
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If for any the reasons for the deteriorating transparency of the air (smoke, dust), then decreases illuminance photodiode VD2. The current through the photodiode decreases, and the voltage on it the cathode also decreases and becomes less stress on the engine R4. Voltage the output of the operational amplifier DA1 becomes close to the supply voltage, and the element DD1.1 unlocks. On the elements DD1.1., DD1.2. assembled low-frequency generator. On the output 11 of the element DD1.2. pulses appear with a frequency of 4 Hz, which periodically permit the operation of another generator of audio frequency, harvested the elements DD1.3., DD1.4. and generating a signal at a frequency of 1000 Hz. Piezoceramic emitter BA1 plays an intermittent alarm when this also lights up the led VD3. Structurally, the sensor comprises two opaque tubes with a diameter of 4 mm and a length of 75 mm. the edges of the tubes inserted led photodiode VD1 and VD2. Other edges of the tubes facing each other. When this arrangement, on the photodiode is not influenced by extraneous infrared radiation.
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