Developing a System for Maintaining Ozone Levels in a Controlled Environment

A method for monitoring and maintaining ozone levels in a reaction chamber was developed. Process control methods and a base software system were developed and calibrated. A user-friendly interface was also created.  Previously, it has been difficult to maintain constant ozone levels in the reaction chamber and most experimentalists have simply added an initial amount of ozone that was depleted with time.  While convenient and considered a standard technique in the field, this method is not representative of the ambient atmospheric environment.   We used a PID control system that would be able to maintain the ozone levels both efficiently and in a timely manner. The software to maintain the ozone levels was developed in LabVIEW, a program using a visual programming language. With this program, appropriate software was developed that would take in external data from an ozone meter, record and interpret it, and translate it into a usable signal that would be sent to an ozone generator, which would finally correct the ozone level in the reaction chamber. The hardware system assembled consisted of the previously mentioned ozone meter measuring the current ozone level in the reaction chamber, a computer which was situated in the lab and ran the designed program, a DC conversion box which interpreted the signal from the software and converted into a usable DC current, a AC conversion box which converted the DC current to a AC current, and the abovementioned ozone generator, which was powered from the AC conversion box. The calibration of the system involved determining the appropriate constants to use for the PID control system, which were originally determined using the Ziegler-Nichols tuning method and then heuristically altered to better control the ozone levels. The user-interface was further developed to include a computerized recording and transcribing of the ozone levels in the chamber, an ozone purge mode where the program would deactivate until the ozone levels reached zero, at which point it would start up again, and a bypass mode where the user could selectively add ozone without the PID controller correcting the ozone level.

            The control system developed introduces an exciting new opportunity for the study of atmospheric chemistry. In real world environments, ozone levels, on average, remain relatively constant within a given biome. However, in prior research, ozone was left to deplete to zero during the course of an experiment. Utilizing the new system, ozone levels can be maintained at any desired level, just as it would be in any real environment. This will allow for more accurate interpretations and understandings of the reactions that are studied in the laboratory.