The HygroTrace from GE Sensing, Billerica, MA, measures moisture to the low ppb range for ultra-high purity gases critical to various semiconductor, LCD, and other manufacturing processes. The device uses aluminum oxide technology with a newly patented technique to improve sensor speed of response, providing ppb moisture measurement in minutes. The sensor applies a temperature pulse to dry the sensor. The readsorption rate is measured while holding a constant sensor temperature; this is proportional to the moisture concentration in the sample gas. Output is a 4–20 mA signal proportional to a user-programmed range.