Abstract: A gas analyzer has a simple composition and can measure multi-components at a high accuracy. A plurality of measuring cells, including a case where the cells are different in length from each other, communicate sequentially with each other through a communication part to form a single gas path. A cut-on filter as an infrared penetration/reflection means for diffracting spectrally an infrared wavelength is provided on a light source side. A NO.sub.X measuring cell 3 having a cell length of about 60 mm and a CO.sub.2 measuring cell 7 having a cell length of about 1 mm which communicate through the communication part with each other, and a capacitor microphone (an infrared-ray detector for NO.sub.X) and a pyroelectric detector (an infrared-ray detector for CO.sub.2) are provided on the infrared penetration and reflection sides of the optical filter.

Abstract: An ultraviolet light source is provided on one end of a cell into which a sample gas is introduced. A beam splitter for dividing beams which have been transmitted through the cell into two optical paths is provided on the other end of the cell. A first detector is provided in one optical path, and a second detector is provided in the other optical path. A gas filter filled with a component to be measured is positioned between the detectors and beam splitter so that a concentration of the component to be measured may be obtained on the basis of a difference between the output of the first detector and the product of the output of the second detector and an appointed constant. Influences resulting from components coexisting in the sample gas are reduced. Alternatively, an infrared light source may be provided on one end of a sample cell. A gas filter filled with a gas the same as the gas to be measured is provided at the other end of the sample cell.

Abstract: An improved infrared analyzer is provided wherein an unknown specimen gas can be subjected to a measuring infrared ray and a comparative infrared ray to provide resulting signals. The system can be initially calibrated when a zero gas state is initially achieved in the sample cell, and correction factors are achieved by holding the zero gas instrument signal and an output difference between a zero gas comparison signal and the measuring signal for subsequent processing of the actual measurement of the specimen gas to provide a calibrated output signal representative of the concentration of the unknown gas.

Abstract: An amplifying circuit for amplifying an output from a measurement wavelength detector consists of a preamplifier and a measurement signal amplifier provided at an output of said preamplifier. The measurement signal amplifier is provided with an input-resistance and a feed-back resistance, a variable resistance connected in series to a normally open switch, the series combination being connected in parallel to the feed-back resistance so that the gain of the measurement signal amplifier may be variable.