| 摘要 |
PURPOSE:To obtain a humidity sensor with a long life, limited aging, a better exchangeability and a high resolution by connecting one end of a humidity sensitive member to one of two piezo-electric vibrators and the other end thereof to the other piezoelectric vibrator so as to measure the humidity from output of a circuit adapted to determine the difference in the resonance frequency. CONSTITUTION:Crystal resonators 3 and 4 shall be AT cut crystal resonators of the same kind. The temperature characteristic and aging property are roughly equal and the resonance frequency is set almost equal by at f0 when the humidity is at H0%. As the humidity varies from H0% to H%, the resonance frequency of the crystal resonators 3 and 4 changes. The difference DELTAf in the change of the resonance frequency with respect to the change in the humidity is outputted from a mixer 11a. The crystal resonators 3 and 4 are so set that the resonance frequency of one thereof increases but that thereof decrease due to variation in the tension of hair 8. Therefore, DELTAf gives a large value with the respect to the change in the humidity. As compared to the case of using only one crystal resonator, this enables the humidity measurement with a higher accuracy to obtain the humidity H%f from DELTAf. As humidity information can be obtained in conversion to change in the resonance frequency of the crystal resonator, direct digital processing is possible without the use of an A/D converter. |
