Dynamic calibration method for a trace moisture analyzer based on the quick response of a ball surface acoustic wave sensor

The measurement of trace moisture is important in industry to maintain the quality and yield of products, such as semiconductors, lithium-ion batteries, and organic electroluminescence devices. In the field, on-site calibration of a trace moisture analyzer is required to maintain its reliability. Given these circumstances, we previously developed a ball surface acoustic wave (SAW) sensor using SAW on spherical piezoelectric elements and reported its quick response as its advantage over other trace moisture analyzers. However, the ultimately short response time of less than 1 s has not been verified, and it has not yet been calibrated on-site. In this study, we developed a system for the injection of saturated water vapor to evaluate the quick response of a trace moisture analyzer, and we verified the quick response time of as short as 0.64 s. It is the shortest response time reported so far. In addition, to realize its on-site calibration, we developed a dynamic calibration method, which takes only 10 min, by the injection of saturated water vapor, in contrast to the presently available static calibration method that takes 10 h. Since this system consists of simple components, it can be downsized. Moreover, because it uses a small amount of saturated water vapor as the calibration gas, it is easy to prepare calibration gases in the field and may be applied to on-site calibration.