Abstract
The near-infrared hygrometer for measuring perspiration is developed. Temperature-controlled PbS detector is used as the sensor of the near-infrared beam. Long terms experiments show that the resistance of PbS detector increases as ambient temperature rises and the negative errors in the near-infrared hygrometer appear. In order to compensate those errors, the correcting factor C(C=Qs/Qm, where Qs is water vapor concentration (g/m3) calculated from the temperature of the saturator, Qm is the measured value by the near-infrared hygrometer) is introduced. Also, the resistance factor D regarding the resistance of PbS detector (D=(1/RL-1/RD), where Rl, RD are light and dark resistance of PbS detector) is defined.
To obtain the relation between the resistance factor D and the correcting factor C, it is proposed as a expedient method that the light source voltage is varied to change the resistance factor D. From the measured values of Qs and Qm by this method, the factor C is calculated for each values of D. The relation between D and C is formulated by the curve fitting method and used for compensation of the near-infrared hygrometer. The accuracy of the compensated near-infrared hygrometer better than 2% is obtained for long terms.
