Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1989-08-22
1991-06-25
Wieder, Kenneth
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
733365, 324694, 324606, G01R 2708
Patent
active
050270770
ABSTRACT:
A humidity sensing apparatus which includes a humidity sensor which detects humidity as a function of impedance is provided. A reference resistor has a predetermined resistance value. A charge switching circuit selectively couples one of the reference resistor or the humidity sensor in series with a reference capacitor which has a predetermined capacitance. A voltage judging circuit determines whether the terminal voltage of the reference capacitor is high or low. A charge/discharge switch selectively charges and discharges the reference capacitor in accordance with the output of the voltage judging circuit. A sensor direction switching circuit inverts the direction of current flowing through the humidity sensor during charging of the reference capacitor. An oscillation frequency counter counts the number of charge/discharge cycles which are repeated during a predetermined time period. A humidity sensor resistance value calculating circuit calculates the resistance value of the humidity sensor in accordance with the number of repeated charge/discharge cycles when the reference capacitor is coupled to the reference resistor for charging and the number of repeated charge/discharge cycles when the reference capacitor is coupled to the humidity sensor during charging. A humidity determining circuit determines the humidity from the resistance value of the humidity sensor calculated by the humidity sensor resistance value calculating circuit.
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Ikejiri Masahisa
Inoue Kunihiro
Miyazaki Hajime
Muranaka Tsukasa
Uchiyama Shouichi
Mueller Robert W.
Seiko Epson Corporation
Wieder Kenneth
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