Patent ID: 7971482

Claim:
A humidity sensor for detecting humidity in atmosphere comprising: a humidity sensing element including a humidity sensitive film and a pair of first electrodes; a processing circuit, wherein: the humidity sensitive film has a dielectric constant, which is variable in accordance with moisture adsorbed in the humidity sensitive film; the pair of first electrodes detects capacitance of the humidity sensitive film and outputs a signal corresponding to the capacitance; the processing circuit processes the signal from the pair of first electrodes; the humidity sensor is a capacitive humidity sensor for detecting relative humidity based on the dielectric constant of the humidity sensitive film; the humidity sensitive film is made of inorganic material having a plurality of fine pores for adsorbing the moisture in the atmosphere; a diameter of each of the fine pores is disposed within a range around a predetermined center value so that capillary tube aggregation phenomenon occurs at a predetermined relative humidity; the capillary tube aggregation phenomenon is defined in such a manner that a plurality of water molecules in the atmosphere rapidly penetrate into the fine pores at the predetermined relative humidity; the capacitance of the humidity sensitive film has a change rate with respect to the relative humidity; and the change rate of the capacitance when the relative humidity in the atmosphere is higher than the predetermined relative humidity is larger than the change rate of the capacitance when the relative humidity in the atmosphere is lower than the predetermined relative humidity; and a capacitive element having a pair of second electrodes, wherein the capacitive element has a capacitance, which is substantially constant with respect to the relative humidity; the processing circuit includes a C-V converter circuit for converting a capacitance difference between the pair of second electrodes and the pair of first electrodes to a voltage; and the humidity sensor detects the relative humidity based on the voltage output from the C-V converter circuit, wherein: the processing circuit further includes a first amplifier and a second amplifier; the first amplifier amplifies the voltage output from the C-V converter circuit with a first amplification factor so that the relative humidity higher than the predetermined relative humidity is detected; and the second amplifier amplifies the voltage output from the C-V converter circuit with a second amplification factor so that the relative humidity lower than the predetermined relative humidity is detected.