| 摘要 |
<p>Apparatus for the ratiometric measurement of a quantity of liquid in a tank includes first and second capacitors (6,8) disposed in a tank and responsive to an AC excitation signal (2). The output signal from the first capacitor (6) corresponds to the quantity of liquid in the tank, while the output signal of the second capacitor (8) corresponds to an empty tank condition. First and second rectifier units (D1,D2; and D3,D4) are respectively coupled to the first and second capacitors (6,8). A first current-to-voltage converter (14) is coupled to both the first and second rectifier units (D1,D2; and D3,D4) and provides a first voltage signal corresponding to the first and second rectified signals. A second current-to-voltage converter (18) is coupled to the second rectifier unit (D3 and D4) and provides a second voltage signal corresponding to the second rectified signal. A ratio device (20) is coupled to the outputs of both voltage-to-converter means (14 and 18) and forms a ratio of the first and second voltage signals to provide an output signal indicative of the quantity of liquid in the tank. This output signal is insensitive to diode characteristics and variations in the excitation voltage and frequency, and produces a true zero output when the sensed quantity of liquid in a tank is zero.</p> |
