| 摘要 |
PURPOSE:To enable detection of water level with a simple circuitry, by detecting changes in acoustic impedance of a piezo-electric vibrator under water and in the air as such in the frequency. CONSTITUTION:Frequency of an output of an INV 11 is adjusted with a variable resistor 7 near a resonance point of a piezo-electric vibrator 5. A voltage deter mined by a voltage division ratio of impedance at the resonance point of a resistance 4 and the piezo-electric vibrator 5 is generated at a connection point between the resistance 4 and the piezo-electric vibrator 5 connected in series to the output of the INV 11. The voltage is fed back to the connection point between the variable resistance 7 and a capacitor 8 of an oscillation circuit 1 through a capacitor 12. As a vibration surface of the piezo-electric vibrator 5 is suppressed on the water surface or under water to change electric character istic, a feedback voltage varies with the capacitor 12 and thus, the frequency of an output of the INV 11 deviates significantly. |
