Respiratory gas concentration measuring apparatus

摘要

A respiratory gas concentration measuring apparatus includes a chopper having a first filter for passing therethrough light from a light source and having a first wavelength which can be absorbed by a gas to be measured and a second filter for passing therethrough light from the light source and having a second wavelength which cannot be absorbed by the gas. The chopper is rotatable to position the first and second filters alternately in a light path. The light having passed through the filters is converted by a photodetector into an electric signal. A first detector detects an output from the first filter based on the electric signal, and a second detector detects an output from the second filter based on the electric signal. The apparatus has a power computing circuit for raising an output from said second detector to an mth power, m being a power exponent preset in the power computing circuit, and a divider circuit for dividing an output from the first detector by an output from the power computing circuit. The power exponent m is the ratio between a temperature-dependent coefficient theta 1 of the output of the first detector which varies exponentially with a temperature variation and a temperature-dependent coefficient theta 2 of the output of the second detector which varies exponentially with a temperature variation.