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The gas overranging alarm miner lamp 4

2016-08-14 10:49  
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The gas overranging alarm miner lamp 4
The working principle: The gas overranging alarm miner lamp circuit is composed of gas detection circuit, multivibrator, audio output circuit and lighting circuit. It's shown as the figure 8-32. Gas detection circuitis composed ofthe gas sensor and resistors R2, R3. Multivibrator is composed oftwo NAND gates Dl, D2 of internal NAND gate and resistors R4 and R5, capacitor C2. Audio output circuit consists of resistors R6, audio amplification V and speaker BL. Lighting circuit is composed of the battery GB, lights EL andK light switch. When the indoor concentration of combustible gasis inthe allowable range (less than limit value), the resistance between the gas sensors A, B is high,the foot voltage of Ic is low, multivibrator does not work, the speaker BL has no sound. When the indoor concentration of combustible gasis over the limit, the resistance between the gas sensors A, B declines,the foot voltage of Ic is higher than conversion voltage of D1, multivibrator works,the output oscillation signal frompin 4of IC. The signal amplified by the V will promote the speaker BL.