| 摘要 |
PROBLEM TO BE SOLVED: To provide a suitable sensor circuit for using as a burglar alarm, which is reliable with no malfunction caused by noise that is input from a capacitance sensor and a cable due to deterioration of a recent electromagnetic environment, and can detect a change of a capacitance with no influence caused by the capacitance temperature of the capacitance sensor and a temporal capacitance deviation. SOLUTION: The capacitance sensor circuit is provided with a phase shifting type of sinusoidal oscillator 1, a two-phase buffer 2 with the difference of 180 degrees in phase that receives a signal from the oscillator 1 to transmit a capacitance adjusting part 3, the capacitance adjusting part 3, an I-V converting part 4 that is connected to the adjusting part 3, a BPF(band-pass filter) 5 that is connected to the I-V converting part 4, an alternating current amplification 6 that is connected to the BPF 5, a synchronizing detecting part 7 that is connected to the amplification 6, a synchronous signal generating part 8 that is connected to the detecting part 7 and transmits a signal to the detecting part 7, an LPF(low-pass filter) 9 that is connected to the detecting part 7, a direct current amplification 10 that is connected to the LPF 9, a DC servo 11 that is attached to the amplification 10, and a voltage comparing driver 12 that is connected to the amplification 10.
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