Instrument for determining ozone concentration

A method of controlling the concentration of ozone in a body of gaseous fluid in a controlled environment, comprising the steps of:

• a) determining the concentration of ozone in the body of gaseous fluid using an instrument for determining ozone concentration in a gaseous fluid comprising a chamber, at least one filter adapted to remove particulates from gaseous fluid entering the chamber, and at least one filter adapted to remove ozone from gaseous fluid entering the chamber, at least one element arranged to draw gaseous fluid into the chamber at atmospheric pressure, an exhaust, an ultra-violet source located at one end of the chamber and configured to generate a substantially collimated beam of radiation having a wave length in the range 240 to 290 nm, and an ultra-violet sensor arranged at the other end of the chamber and configured to receive the ultra-violet light emitted by the said ultra-violet source, by performing the method steps of:
• i) drawing gaseous fluid through the filter adapted to remove ozone from said gaseous fluid into the chamber to fill said chamber with ozone free gaseous fluid;
• ii) powering the ultra-violet source and measuring the output signal of the ultra-violet sensor I0;
• iii) drawing gaseous fluid through the filter adapted to remove particulates from said gaseous fluid into the chamber to fill said chamber with gaseous fluid potentially burdened with ozone;
• iv) powering the ultra-violet source and measuring the output signal of the ultra-violet sensor Ic;
• v) running the algorithm embodied in the controller to establish ozone concentration;
• vi) issuing a signal representative of ozone concentration;
• and
• b) increasing the ozone concentration in the body of gaseous fluid by introducing ozone into the body of gaseous fluid, and/or reducing the concentration of ozone in the body of gaseous fluid by venting gaseous fluid burdened with ozone from the controlled environment.