| 摘要 |
PURPOSE:To make a dew point measuring apparatus inexpensive, by changing the oscillation frequency of a square wave pulse signal corresponding to humidity change and temp. change and performing operation using the oscillation frequency of the humidity change and that of the temp. change. CONSTITUTION:In a square wave pulse oscillator 1, the resistance RH of a humidity detection element 3 changes by environmental humidity and the oscillation frequency fH changed corresponding thereto is detected. The frequency of a reference resistor element 11 is set to f0 and the ratio of the frequencies fH, fO is operated by a microcomputer (CPU) 9. The resistance RH is calculated from said ratio by CPU 9 and relative humidity H is calculated from the data stored in CPU 9. Further, the resistance RT of a temp. detection element 13 changes by environmental temp. and frequency fT changed corresponding thereto is detected and the ratio of the frequencies fT, fO are operated by the microcomputer 9 and temp. T is calculated from the data stored in CPU 9. A dew point becoming a saturation steam value is calculated from the relative humidity H at the temp. T. Therefore, an expensive A/D converter is made unnecessary and an apparatus can be miniaturized.
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