Patent ID: 8629397

Claim:
A spectrophotometer, comprising: a light source for irradiating light into a sample gas; a photodetector for detecting light transmitted through the sample gas; an optical filter arranged between the light source and the photodetector; and an operation device for calculating a concentration of an actual gas to be measured, contained in the sample gas based on a detection signal value obtained from the photodetector, wherein the operation device calculates the concentration of the actual gas based on a function α for associating a concentration of a substitute gas with a concentration of the actual gas that are obtained from a reference instrument that is an individual instrument body serving as a reference, a function β for associating a relation between a light absorption of the actual gas and a light absorption of the substitute gas in the reference instrument, with a relation between the light absorption of the actual gas and the light absorption of the substitute gas in a calibration instrument that is an individual instrument body to be calibrated, and a function indicating a relation between the concentration of the substitute gas and the detection signal value from the calibration instrument.