A programmed feedback control of solvent vapour concentrations in experimental inhalation chambers.

This paper describes a computer-controlled system to regulate solvent vapour concentrations in experimental inhalation devices. This system consists of an exposure chamber, a bubbler with a mass flow-meter, a monitor gas chromatograph and a computer. The frequency of automatic sampling was dependent upon the retention time of test materials. Flow-rate was corrected through a computer regulated bubbler as soon as the mean chamber concentration varied by more than 2.5% of a command level. Regulation coefficients were calculated by relating the concentration of vapours sampled with adsorbent tubes to the mean peak areas given by the monitor gas chromatograph. They were then fed into the computer allowing the actual concentration to be adjusted to the command level. Deliberately induced fluctuations in the level of acetone, ethanol and trichloroethylene, either sudden or progressive, were satisfactorily corrected as were fluctuations occurring normally during repeated exposures to ethanol. Variations were generally inferior to 5% of the command level.