STABLE GASEOUS ATMOSPHERES FOR NOSE-ONLY INHALATION USING MASS FLOW CONTROLLERS

Abstract

The maintenance of stable test atmospheres in small-volume inhalation systems such as a nose-only exposure manifold requires rapid and appropriate responses to fluctuations in a number of parameters. For example, changes in flows or voltages can affect test compound generation efficiency and gas dilution ratios, resulting in excursions of the test concentration outside an acceptable range. A feedback control loop was designed that makes use of mass flow controllers in maintaining the target concentration of a test compound. The system was tested by generating ozone in a nose-only exposure manifold. An ozone analyzer provided updated concentration values every 30 s, which were compared to the user-defined target concentration recorded in the interface readout box. Values of gain, integral, and lead determining an appropriate response of the controller to concentration fluctuations were implemented based on proportional-integral-derivative control algorithms. Using this approach, the flow of ozone mixed with dilution air into the system was adjusted as required without user intervention, minimizing concentration overshoots upon system startup, maintaining an ozone concentration within a range 5% of the target concentration, and responding rapidly and efficiently to line disturbances.

Keywords: :

• Feedback Control, Mass Flow Controller, Nose-only Inhalation, Ozone, Pid