| 摘要 |
The proposed optoelectronic fire alarm unit contains a power-supply unit, a sensitive circuit, fire detectors, and an indicator. The number of the fire detectors is equal to the number of monitored positions. Each fire detector contains two complementary field-effect transistors. The sources of the transistors are connected together. The gate of each transistor is connected to the drain of the other transistor via a thermistor with a positive temperature coefficient of resistance. Between the gate and the source of each transistor, a photoresistor with a negative temperature coefficient of resistance is connected. The sensitive circuit contains a transformer and a capacitor, which is connected to the primary winding of the transformer. The said primary winding and the capacitor form a parallel resonance circuit, which is connected in series between the terminals of the fire detectors that correspond to the same polarity of power-supply voltage and the corresponding terminal of the power-supply unit. The terminals of the fire detectors that correspond to the opposite polarity of power-supply voltage are connected to the other terminal of the power-supply unit. The indicator is connected across the secondary winding of the transformer of the sensitive circuit. The proposed device is sensitive to temperature increases or infrared radiation and consumes low current in the waiting mode. Due to this feature, the device can be used in fire alarm systems designed for monitoring objects with large dimensions as well as objects with power supply from low-power self-contained power-supply sources such as accumulator or solar batteries. |
