Melting-point hygrometer with temp. sensor in cooled transparent element for measuring water content in medium

摘要

The glass prism (2) contg. a temp.-sensitive resistor (9) is set up in the path of the beam from a laser (4) and beam-shaper (5). The beam passes through the lower third of the prism to a phototransistor (6) while the medium (e.g. moist air) flows past the prism in a measurement chamber (1) between its inlet (7) and outlet (8). The phototransistor registers the variation in brightness caused by increased scattering as the boundary (14) of the frosted area encroaches on the laser beam. An electronic circuit regulates a Peltier cooler (3) to maintain the boundary at a constant level.