AUTOMATIC FEEDBACK-CONTROL OF A VAPOR GENERATION SYSTEM USING OFF-THE-SHELF COMPONENTS

A solvent vapor generation and control system was assembled that provi ded accurate and reliable vapor concentrations over extended periods, functioned without operator intervention, used only off-the-shelf hard ware and software components, and required no special programming or e lectronics expertise to construct, configure, or operate. Evaluations using toluene demonstrated excellent concentration control over 4- to 72-h periods of unattended operation. Time-weighted average toluene co ncentrations were maintained within 1 ppm of the target over a range o f 100-900 ppm, with root-mean-square variability about the setpoint of 3-5% of setpoint for all but the lowest setpoint used. Concentrations were maintained within 5% of setpoint 80-90% of the time for higher s etpoints, and within 10% of setpoint over 95% of the time for all but the lowest setpoint used. Excursions of more than 10% above or below t he setpoint were rare. Reduced control effectiveness at the lower setp oints was attributed to inherent but reducible limitations in the syst em's design and operating mode. The system clearly demonstrated that a ccurate, precise, and reliable systems may be constructed and operated without the need for custom hardware or software development or speci al expertise in either electronics or computer programming. Additional study is needed to evaluate the performance of this and similar syste ms with the range of volatile and semivolatile materials of health or materials science interest; however, there appears to be no inherent l imitations in the technology that would prevent its ready application to a variety of research uses.