| 摘要 |
PURPOSE:To prevent the variance of a humidity measured value due to temperature by converting digitally the output of a humidity sensor in a wide dynamic range by a logarithmic A-D converter and converting the counted value of the number of pulses to a humidity value and displaying this value. CONSTITUTION:The output of the ceramic humidity sensor is led to a logarithmic A/C converter 5, and in the converter 5, a capacitor 18 is charged during the time when a preliminarily determined number N of clock pulses are obtained by a counter 19, the capacitor 18 is discharged through a resistance 16 when this number of pulses are counted, and an exponential-functionally changing voltage is compared with a set reference value ER. A ratio of the period (reference time) from the charging start point to the discharging start point to the period from the discharging start point to the time when compared values coincide with each other is operated, and the humidity is displayed on a display device 21. Thus, an analog logarithmic converting circuit and the A/D conversion are omitted to make the circuit constitution simple and low-cost. |
