Measuring and testing – Fluid pressure gauge – With pressure and/or temperature compensation
Patent
1986-04-29
1987-08-04
Woodiel, Donald O.
Measuring and testing
Fluid pressure gauge
With pressure and/or temperature compensation
73718, G01L 912, G01L 1904
Patent
active
046837540
ABSTRACT:
A capacitive displacement type transducer, wherein the oscillation frequency of a self-excited oscillator circuit including a pair of differential capacitors formed with a movable electrode disposed between two outer electrodes is counted by a counter, the output level of the counter is reversed each time a certain count is attained to cause the differential capacitances to be switched alternatively, and to make identical the respective reversal periods, and application voltage to be applied to the differential capacitors being controlled by an integrator, and a voltage relating to the output of the integrator being applied through a fixed impedance to the movable electrode, thereby eliminating fixed capacitances formed across the difference capacitors. Also, a voltage generated by dividing and averaging the output level of the counter by use of a certain pulse duration of a monostable circuit operating in synchronism with a counter, is used to compensate for static pressure changes. Also, a temperature sensing element is included in a converting section to perform temperature correction. The circuit may be used in a two wire transmission system. The circuit improves upon the prior art by eliminating heretofore used complex circuits, thereby increasing reliability, efficiency and reducing size.
REFERENCES:
patent: 4387601 (1983-06-01), Azegami
patent: 4467655 (1984-08-01), Lee
patent: 4550611 (1985-11-01), Czarnocki
patent: 4625560 (1986-12-01), Sanders
Azegami Tadashi
Hirata Terutaka
Katayama Megumi
Kimura Atsushi
Kojima Moonray
Woodiel Donald O.
Yokogawa Hokushin Electric Corporation
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