| 摘要 |
The dew-point hygrometer has, as usual, a dew-point mirror (1), a temperature-control circuit comprising a heating and/or cooling device (7) and a temperature sensor (5) for measuring the temperature of the mirror surface. A light source (10) produces a measuring light beam (LM) directed at the mirror surface, and a photodetector (22) receives the light (LF) reflected from the mirror surface and provides an output signal which is fed to the control circuit of the heating and/or cooling device (7) as a control variable. The light of the measuring light beam (LM) is situated in a narrow wavelength range, whose centre wavelength is absorbed by water in the solid and/or liquid state of aggregation. Preferably, the wavelength range has a centre wavelength of 3.0 mu m and a half-peak width of about 450 nm. In addition, a reference light beam (LR) whose light is situated in a different wavelength range can be directed at the dew-point mirror (1) at the same time as, or alternating with, the measuring light beam (LM); in that case, a signal corresponding to the ratio of the reflected light components is formed in the control circuit as a control variable. <IMAGE>
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