Module for measurement of CO 2 concentration in exhaled air

Abstract

The obj ective of this work consists in working out of a detection module for capnography (carbon dioxide concentration measurement in anaesthesiology and intensive care). The principle of operation of the module consists of the NDIR method. The basic assumption for construction ofthis model was using of directly modulated thermal JR source in it. A few models of JR sources were worked out. Their heaters were made from thick platinum layers and foil. Limits of modulation frequency for JR sources were greater than 30 Hz.The detection module consists of an optical part, analogue electronics and microprocessor system with a suitable program. The time dependent concentration of C02, end tidal concentration of C02, mean concentration of N20 and breath frequency are output values of the detection module. Measurements are executed 30 times per second. The accuracy of CO2 concentration measurement equals to 5%.

Optical gas sensing: a review

“…Thermal detectors also tend to be optimized for use at low frequencies, with the result that 1-2 Hz operation is common, at which frequency 1/ f noise can be problematic. For certain applications, such as capnography, faster response times also dictate the use of frequencies of 30 Hz or more [89]. A final disadvantage of the standard microbulb is that its glass envelope has negligible transmission at wavelengths longer than 5 μm [79], and therefore for certain gases that absorb at longer wavelengths, alternative packaging is required.…”