A new type of dynamic optical dew-point sensor using a laser diode and an optical fiber cable

A new type of optical dew-point sensor using a laser diode and an optical fiber cable has been devised. The measurement motion of the sensor is based on the control of quantity of dew deposited on a gold plate with rough surface oscillatory at low level with time by using a proportional control circuit with an integrator. The intensity of scattered light from the surface of the plate is inversely proportional to the quantity of dew deposited on the surface so that the dew points could be determined dynamically at the maximum and minimum points of the intensity of scattered laser light at which dew begins to deposit and also to disappear. Dew points ranged from -3/spl deg/C to 40/spl deg/C were measured in the atmosphere from 10/spl deg/C to 50/spl deg/C with an accuracy of /spl plusmn/0.5 /spl deg/C that was /spl plusmn/2%RH with the time interval of measurement from 31sec to 6sec.