| 摘要 |
PURPOSE:To accurately measure the concn. of gas, by eliminating the variation in a measured value caused by the detection of the non-linearity of a detector. CONSTITUTION:Receiving power signal correction means 19, 20 preliminarily store correction factors making the respective detection characteristics of the first and second detectors 5, 12 linear and correct the receiving power signal quantities on the basis of said correction factors corresponding to the receiving power signal quantities detected by the first and second receiving power detection circuits 13, 14. Differential signal correction means 21, 22 preliminarily store correction factors for correcting differential signal quantities to the receiving power quantities and correct the correction factors corresponding to the differential signal quantities detected by the first and second differential signal detection circuits 15, 16. By this method, by correcting the variation in the receiving power signal quantities to the change in light receiving quantity and the differential signal quantities to the receiving power signal quantities, the variation in a measured value caused by the non-linearity detection characteristic of a detector is eliminated and the concn. of gas to be measured can be accurately measured.
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