Gas detector

Details Gas detector Gas detector

1995-08-24

1997-06-10

Hannaher, Constantine

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

25033913, G01N 2135

Patent

active

056378726

ABSTRACT:
A gas detector of gas in a target zone has a transmitter of frequency modulated light and a receiver. In the receiver, a homodyne detection circuit mixes a detected signal with a reference signal at one of the modulation frequencies, where the reference signal has been derived from light that has passed through the target zone. The homodyne detection circuit includes a bandpass filter, amplifier, phase lock loop and phase shifter. Etalon fringes are reduced by moving them to high frequencies and filtering them out. Gas density is measured by comparison of the detected signal from the target zone with a signal from a gas reference cell. A method of detecting gas includes transmitting frequency modulated light through a target zone, receiving the light, and homodyne detection of the detected signal by mixing the detected signal with a reference signal at one of the modulation frequencies, where the reference signal has been derived from light that has passed through the target zone.

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Fiber-optic evanescent-wave methane-g

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