Patent ID: 6326620
Filing Date: 2001-12-04
Classification: G01J

Abstract:
A detection system for use in connection with a DC infrared emitter in an NDIR system comprising:an infrared detector in an NDIR system;a modulator for chopping a DC signal from said infrared detector into components having a first predetermined frequency of about 1 kHz;an amplifier coupled to an output of said modulator for amplifying signals from said modulator;a demodulator coupled to an output of said amplifier and synchronized with said modulator for providing a DC level output signal therefrom;a filter coupled to an output of said demodulator for filtering out signal components above a second predetermined frequency of about 3 Hz;an A-to-D converter coupled to said filter for providing a binary signal output representative of the DC signal at the output of said filter;an oscillator having a frequency of approximately 1 kHz and wherein said modulator and said demodulator are coupled to said oscillator, wherein said modulator includes a solid state analog switch coupled to said oscillator; andwherein said demodulator includes an operational amplifier and a solid state analog switch coupled to said oscillator for inverting one half of each cycle of signals from said amplifier.