Design and evaluation of a low-cost photometer for measuring ozone gas concentrations

Abstract

Ozone is used in various fields such as water purification, chemical processing, and medicine. Especially for measuring ozone concentrations during medical therapy, photometry is the most suitable method as it allows in-line measurements at a low measurement temperature with fast response times. However, photometers for ozone typically cost several thousand euros. The main goal of this thesis is to create a portable, low-cost photometer for measuring ozone concentrations (0.4 - 2.0 vol%) in an oxygen-ozone gas mixture with a reaction time of less than 1 s. Based on that, a concept is designed to ensure a well-functioning photometer with optimal use of the light emitted from the light source. A second concept that omits optical components, therefore losing light utilisation and saving costs is developed for comparison. Both concepts feature a dual-beam configuration with a single light source and a main and reference sensor as well as a 5 mm optical path. All necessary parts, including a 280 nm LED and a quartz glass cuvette, are selected and matched for the technical implementation. The electronics, with a Raspberry Pi as a centrepiece and a 16 bit analogue digital converter, are the same for both setups. After construction and implementation of parts and measurement procedures in Python code, preliminary tests are conducted, for finding a suitable mode of operation. Calibration and measurements for the subsequent evaluation of both devices are conducted. Results show that both concepts have a similar performance with a linear range of 0.7 - 2.5 vol%, a reaction time of 210 ms, and a relative error of less than 2.7%. Temperature fluctuations appear to be the major cause for errors. The cheaper concept costs about 600€ in materials and has definite potential for further reduction in both cost and size.