Ozone detection in air or process gas for low concn. determn. - by periodically switching sensor feedline to line contg. ozone filter and utilising semiconductor sensor element for continuous ozone detection by resistance modification

摘要

The central control and evaluation unit (6) evaluates the electrical signals of an ozone sensor (3) by the following methods: (a) the control unit (6) passes the test gas stream, periodically in freely selectable fixed time intervals, through a feedline branch (A), contg. a wideband gas filter (4) which is also active for ozone, or through a feedline branch (B) to the sensor (3) and determines the ozone concn. from the sensor signal difference of the feedline states (A) and (B); or (b) the control unit (6) periodically switches between two feedline branches (A,B) and, when a freely chosen sensor signal difference is exceeded, is switched repeatedly, independently of the period duration, from branch (B) to branch (A) contg. a wideband gas filter (4) which is also active for ozone, and the ozone concn. determined from the opening times of branch (B). The ozone sensor (3) is pref. a semiconductor sensor element, the resistance of which is modified by the ozone at a pref. sensor material surface temp. The feedline branch (B) may also contain a wideband gas filter (10), and which is inactive for ozone. ADVANTAGE - The appts. and determn. allows continuous and inexpensive detection of ozone even at below the max. work place concn. (0.1 ppm), require less maintenance and may be operated without special skill.