Pneumatic thermometer

Claim 1

Apparatus for measuring the temperature of a gas flowing through a duct, said apparatus comprising: a. a fluid-operated oscillator so positioned in said duct that a portion of said gas flows through said oscillator while a portion of said gas flows around said oscillator, said oscillator comprising: 1. a generally bell-shaped intake channel adapted to receive a portion of said gas, 2. resonant chamber, 3. an input nozzle interposed between said intake channel and said resonant chamber, 4. a stilling chamber, 5. a pair of jet edges symmetrically disposed about the axis of said input nozzle between said resonant chamber and said stilling chamber and, 6. an egress nozzle providing an exhaust from said stilling chamber and having a substantially smaller diameter than said input nozzle, so that the velocity of flow of gas past said jet edge approaches but does not exceed a predetermined limiting velocity regardless of increases in the pressure or velocity of the gas at said input nozzle, b. thE fundamental frequency of said oscillator being determined by the dimensions of said resonant chamber in relation to the velocity of sound in the gas within said resonant chamber, said velocity being dependent on temperature and substantially independent of pressure, c. a pressure sensitive electrical transducer at a location remote from said resonant chamber, d. a tube conducting an acoustical signal from said resonant chamber to said transducer, e. cooling means for preventing the temperature of said transducer from rising to an excessive value regardless of the temperature of the gas in said duct and in said resonant chamber, f. pulse-frequency-to-voltage converter means for converting the electrical output of said transducer to a voltage the amplitude of which is proportional to the frequency of said acoustical signal, and g. a temperature-calibrated voltmeter for measuring the output of said converter.