基本信息
摘要：978,143. Electric meters; electric bridge circuits; liquid level measuring apparatus; indicating apparatus. BENDIX CORPORATION. March 14, 1963 [March 26, 1962], No. 10212/63. Headings G1J, G1N, G1Q and G1U. [Also in Divisions G4 and H3] The output voltage of a capacitive liquid level measuring bridge uses a circuit comprising a number of transistors of opposite conductivity type are arranged in cascade such that as the D.C. input signal rises the output voltage first rises and then falls. Fig. 1 comprises two such cascades in succession so that the final output voltage rises and falls twice. It is explained mathematically that so long as the signal voltage is below the level at which the respective output transistors 59 and 72 saturate the gain of each circuits is 2 but when they saturate the output voltage (e.g. E2) is related to the input voltage (e.g. E 1 ) by the relation E 2 = V - 2E 1 where V is the supply voltage. The circuit is used to measure the voltage from a liquid level indicator Fig. 3. The liquid level measuring capacitance 81 is connected in a capacitive bridge fed with alternating current from source 84 and having its output amplified at 85 rectified at 86 and 90 and then applied across a potential variable capacitor 83 in the form of a semi-conductor diode so as to balance the bridge, isolating chokes being provided to separate the A.C. path from the D.C. path. Rectified output from the amplifier is fed to a first meter 93 calibrated in metres and through a folding circuit similar to Fig. 1 to a meter 95 calibrated in decimetres. As the level of the liquid rises from 0 to 1 metre the pointer of meter 93 moves clockwise from 0 to 1 and the pointer of 95 moves in clockwise direction from 0 to 10. A further rise of 1 to 2 metres increases the reading on 93 from 1 to 2 but, as the output of the folding-circuit is now falling, causes the pointer of meter 95 to rotate in an anticlockwise direction towards its initial position, readings being taken from the inner scale. Further rise from 2 to 3 metres causes the pointer of metre 95 to move clockwise again while the rise from 3 to 4 metres causes pointer of metre 95 to return in an anticlockwise direction.
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