Ambient hydrogen chloride sensing with a zinc-coated piezoelectric crystal resonator

The author discusses a simple yet reliable scheme for the selective and sensitive detection of gaseous HCl utilizing a zinc-coated quartz-crystal resonator as the sensing element in a piezoelectric microbalance operating in a frequency-time differential mode. Detection is based on the rapid formation of the hygroscopic ZnCl/sub 2/ salt with the concomitant uptake of water for ambient relative humidities greater than 10%. The sensitivity ratio for detection of HCl as compared to other common ambient gases is 100:1 or greater. The author also discusses the results of small-scale fire tests, conducted in a telecommunications central office (CO), that demonstrate the benefits derived from ambient HCl sensing with an emphasis on the comparison of the response to commercial fire/smoke detection methods. Studies conducted in several COs have shown that sensor lifetime is expected to exceed about three years.<>