Measuring and testing – Gas analysis – By vibration
Patent
1997-03-12
1998-11-03
Gregory, Bernarr E.
Measuring and testing
Gas analysis
By vibration
73 232, G01N 2902
Patent
active
H00017566
ABSTRACT:
A differential refractometer measures the difference of refractive index of electromagnetic centimeter waves of samples of gas with high sensitivity, and can be used to measure the gradient of refractive index of electromagnetic waves in air, and more particularly, to measure radar ducting conditions low over bodies of water. The instrument uses two microwave oscillators, each with its own frequency controlling cavity, with the frequencies of the oscillators differing by a specific value. Air from each of two intakes, vertically separated a specific distance, is directed into each cavity, and the difference frequency measured for a short time, to provide a first measured difference frequency. Then, the air flow from the intakes are cross-fed to the cavities, and the difference frequency is measured for a short time to provide a second measured difference frequency. The difference of refractive index of the air flowing through the intakes is proportional to the difference between the measured difference frequencies. Subsequently, the flow of air through the cavities is alternated periodically, at a rate of about 10 Hz. The drift of the oscillators is mostly eliminated by this method since there is very little frequency drift within the short measurement time.
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