PERFORMANCE OF AN AUTOMATIC FEEDBACK-CONTROL VAPOR GENERATION SYSTEM DURING NEAR-CONTINUOUS INHALATION EXPOSURES

An automatic feedback control vapor generation system constructed from off-the-shelf hardware and software components was used to regulate n ear-continuous animal inhalation exposures to toluene over a 13-day pe riod. The system functioned without operator intervention for up to 23 .7 h/day. For a target concentration of 1000 ppm the system maintained time-weighted average (TWA) exposure concentrations at 1000 +/- 1 ppm after a 30-min ramp-up period, or 992 +/- 1 ppm for the entire exposu re period including ramp-up. Root mean square variability about the ta rget concentration was a maximum of 4%, and was reduced to less than 2 % with minor system adjustments. Excursions above and below the target concentration were similarly reduced to generally less than 5% and ra rely more than 10%. The system's control accuracy and precision over e xtended and repeated exposure periods were exceptional, and exceeded a nything previously reported in the peer-reviewed literature. This perf ormance demonstrated that accurate and precise systems may be construc ted and operated without the need for custom hardware or software deve lopment or special expertise in either electronics or computer program ming, and also demonstrated that such systems may offer reliable and e conomical unattended operation for extended periods.