FY02 Field Evaluations of an In-Situ Chemiresistor Sensor at Edwards Air Force Base, CA
Clifford K. Ho, Lucas K. McGrath, JAMES MAY · 2002
The design, operation, and performance of an in-situ chemiresistor sensor were evaluated during field tests at Edwards Air Force Base in FY02.The primary objectives of the tests were to evaluate the ruggedness of the waterproof sensor housing and to test the operation and performance of the chemiresistor sensor in both the unsaturated and saturated zones of a contaminated well (18-MW37).The housing was tested by lowering it to greater and greater depths beneath the water table over the course of two months.Results showed that the polymer membrane that allows volatile organic compound (VOC) vapors to partition to the sensors inside the housing was able to withstand approximately 30 A (9 m) of water pressure before allowing liquid to penetrate into the housing.Corrosion of the 304 stainless-steel housing was observed, but the integrity of the housing was not compromised during the tests.With regard to the operation and performance of the chemiresistor sensor, tests showed that the chemiresistor was able to operate continuously over a four-month testing period in contaminated and corrosive aqueous environments.Data were logged continuously using a Campbell Scientific CRlOX data logger powered by a 12 amp-hour battery connected to a 20-watt solar panel.Samples taken from the well during the tests (and analyzed in the laboratory) revealed that the concentrations of contaminants (e.g., TCE) in the vicinity of the chemiresistor were lower than the detection limits of the chemiresistor, so direct comparisons could not be made.Results did indicate, however, that the high-humidity environments (100%) caused instability in the chemiresistor readings that produced anomalously high estimates of VOC concentrations.Improvements to both the stability and sensitivity of the chemiresistor sensors are currently being investigated through the use of automated temperature control and an integrated preconcentrator assembly.