This paper describes a flueric gas concentration sensor potentially suitable for determining the concentration of carbon dioxide in respiratory gases. The sensor consists of fluid resistors connected in a bridge circuit and generates a differential pressure signal proportional to the concentration of CO2. The sensor is capable of measuring from 0.07 to 100 percent CO2 in air. The system discussed in this report contains a high-gain laminar proportional amplifier to produce high-level output signals. The amplified sensitivity of the prototype system is 0.6 kPa/percent CO2 (0.09 psi/percent CO2). The experimental results are in agreement with the theoretical analysis and show good linearity and low noise.

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