Gas concentration and/or flow sensor
First Claim
1. A sensor for determining at least one of the bulk flow rate of a gaseous medium and the content of a component of the gaseous medium comprising first and second piezoelectric transducers mounted a predetermined distance apart, said transducers having a predetermined high resonant frequency, a tube extending between said transducers, said tube having a first end adjacent said first transducer and a second end adjacent said second transducer, having a length greater than said predetermined distance and having a predetermined small internal diameter, means for flowing a gaseous medium through said tube, means for alternately applying an electric pulse to said first and second transducers, each transducer establishing a wave which travels through the gaseous medium in said tube to the other transducer in response to an applied pulse, means for measuring the time for each such wave to pass between said transducers, means for measuring the temperature of the gaseous medium flowing through said tube, and means responsive to measured times for the wave to travel in the gas flow direction and to travel opposite the gas flow direction and to the measured temperature for determining at least one of the bulk flow rate of the gaseous medium through said tube and the content of a component of the gaseous medium.
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Reexamination
Accused Products
Abstract
A gas concentration and/or bulk flow rate sensor suitable for measuring the oxygen concentration and the bulk flow rate of gas delivered to a patient for medical purposes. Two piezoelectric transducers mounted on a printed circuit board are interconnected by an elongated coiled tube. The gas is flowed around one of the transducers, through the tube and around the other transducer. Periodically, one of the transducers is energized with a single short duration pulse to transmit a sonic wave through the gas to the other transducer. The travel time for the sonic wave is measured. The two transducers are alternately used as transmitters and receivers so that the wave travel time is measured both with and against the gas flow direction. A thermistor is located in the center of the coiled tube for measuring the temperature of the gas. From the measured times, the measured temperature and stored formulas, a microprocessor calculates the oxygen concentration and/or the bulk flow rate for the gas. The sensor also may be used to measure other components of a gas mixture.
81 Citations
15 Claims
- 1. A sensor for determining at least one of the bulk flow rate of a gaseous medium and the content of a component of the gaseous medium comprising first and second piezoelectric transducers mounted a predetermined distance apart, said transducers having a predetermined high resonant frequency, a tube extending between said transducers, said tube having a first end adjacent said first transducer and a second end adjacent said second transducer, having a length greater than said predetermined distance and having a predetermined small internal diameter, means for flowing a gaseous medium through said tube, means for alternately applying an electric pulse to said first and second transducers, each transducer establishing a wave which travels through the gaseous medium in said tube to the other transducer in response to an applied pulse, means for measuring the time for each such wave to pass between said transducers, means for measuring the temperature of the gaseous medium flowing through said tube, and means responsive to measured times for the wave to travel in the gas flow direction and to travel opposite the gas flow direction and to the measured temperature for determining at least one of the bulk flow rate of the gaseous medium through said tube and the content of a component of the gaseous medium.
Specification