The output of an ozone generator can vary from 2-12% by weight ozone. Knowing the concentration of the ozone and
the flow rate of the gas will determine the output of the ozone generator. This information can be used to control the
overall ozone water treatment process and follow the performance of the ozone generator. These devices, however, are
quite expensive ($5,000 to $10,000) and usually only make sense in applications where knowing the concentration of
ozone in the gas stream is critical or in larger systems where the cost of these instruments is small in comparison to the
overall system price. There are other less expensive ways to estimate the ozone generator output, but they are not as
accurate and do not work in real time.
High concentration monitors work by measuring the amount of ozone per unit volume of gas (g/Nm3). This is typically done by taking a small side stream of the gas and measuring the concentration of this side stream as representative of the main flow. Usually a very good assumption if the system is set-up properly. UV as 254 nm can detect ozone, but does not read oxygen or air. The photometer measures the ozone in the gas stream against a control volume with no ozone. Accuracy is quite high for these systems in the range +/- 1-2%.
Ozone generator manufacturers use such devices to check the performance of their machines prior to shipment. The machines are then shipped with a performance curve that shows ozone generator output as a function of inlet gas flow rate and power setting. A well made machine should conform to these curves and thus minimizes the need for the high concentration monitor. The monitor in this case would either provide a more accurate assessment of the generator performance in real time or serve as a trouble shooting tool.
The performance of the overall system can also be followed by noting the concentration of ozone in the water to be treated. The ozone water treatment system should have been designed on the basis of a certain ozone output from the generator, ozone demand of the water and transfer efficiency of the mixing system. For larger systems, this would be done via a pilot process. Assuming the water quality has not changed, measurements of dissolved ozone should indicate that the generator is providing sufficient ozone to the process.
An emerging technology for measuring ozone employs ultrasonics. These systems utilizes the dependence of speed of sound through gas on gas molecular weight. Ozone generators convert some of the gas at their input to Ozone, thus increasing the molecular weight of the gas. The change in molecular weight of output (Ozone enriched) gas is in direct proportion to Ozone concentration. These systems may offer a low cost method for monitoring ozone concentration from ozone generators in the future.