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Abstract

Method and apparatus for measuring the pressure of a fluid medium, by immersing within the fluid medium an electrical resistor having a resistance varying with temperature; applying electrical current through the electrical resistor to heat it to a predetermined temperature above that of the fluid medium; and measuring the rate of change in resistance of the electrical resistor to produce a measurement of the rate of thermal heat dissipation, varying with the density of the fluid medium in which the electrical resistor is immersed, and thereby a measurement of the pressure of the fluid medium. The electrical resistor is a positive temperature coefficient thermistor driven by a constant voltage source and having a resistance which increases sharply at the predetermined temperature, such that the thermistor is automatically self-controlled to substantially maintain the predetermined temperature, whereby the electrical current drawn by the thermistor is a measurement of the thermal load on the thermistor resulting from the thermal heat dissipation therefrom, and thereby a measurement of the pressure of the fluid medium. Many applications of such method and apparatus are described, including a vacuum gauge, a pressure gauge, a barometer, a Pitot tube type speedometer, and a helicopter blade leak detector.

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First Claim