Highly sensitive humidity sensor for dielectric measurement (water absorption) in glass-fiber resins

The humidity sensor using the sensitive capacitive-dependent crystal is described. Presented is the probe sensitivity (dependence of df on the dCx). In addition, the new idea of excitation of the entire humidity sensor with stochastic test signals is described, and the humidity surface-measuring method is given. It includes the influence of test signals on the weighting function uncertainty and on the A/D-D/A conversion. The results of the air-humidity measurement and water absorption measurement in glass-fiber resins are shown experimentally. The uncertainty of the surface humidity measurement is less than 0.2% (T=15-25/spl deg/C and air-humidity=50 to 98%).