Humidity measuring apparatus
First Claim
1. A humidity measuring apparatus comprising:
- humidity sensor means for sensing humidity as a function of resistance;
a reference resistor having a predetermined resistance value;
a reference capacitor having a predetermined capacitance;
charge switching means for selectively coupling one of said reference resistor or said humidity sensor means in series to said reference capacitor to charge said reference capacitor;
voltage judging means for determining whether the terminal voltage of the reference capacitor is at about a predetermined high voltage (H) or at about a predetermined low voltage (L);
charge/discharge switching means for selectively charging and discharging said reference capacitor in accordance with the output of said voltage judging means producing an oscillating charge/discharge cycle in response to the output of the voltage judging means;
sensor direction switching means coupled to said charge/discharge switching means for inverting the direction of current flowing through said humidity sensor means during at least a portion of the period said reference capacitor is charged through said humidity sensor means in response to the output of the charge/discharge switching means;
determining means coupled to said voltage judging means for determining the resistive value of said humidity sensor means and said humidity as a function of the charge/discharge cycle.
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Accused Products
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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Citations
20 Claims
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1. A humidity measuring apparatus comprising:
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humidity sensor means for sensing humidity as a function of resistance; a reference resistor having a predetermined resistance value; a reference capacitor having a predetermined capacitance; charge switching means for selectively coupling one of said reference resistor or said humidity sensor means in series to said reference capacitor to charge said reference capacitor; voltage judging means for determining whether the terminal voltage of the reference capacitor is at about a predetermined high voltage (H) or at about a predetermined low voltage (L); charge/discharge switching means for selectively charging and discharging said reference capacitor in accordance with the output of said voltage judging means producing an oscillating charge/discharge cycle in response to the output of the voltage judging means; sensor direction switching means coupled to said charge/discharge switching means for inverting the direction of current flowing through said humidity sensor means during at least a portion of the period said reference capacitor is charged through said humidity sensor means in response to the output of the charge/discharge switching means; determining means coupled to said voltage judging means for determining the resistive value of said humidity sensor means and said humidity as a function of the charge/discharge cycle. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A method of avoiding electrolysis in a humidity or temperature sensor comprising the step of alternatively charging and discharging a capacitor through a moisture sensitive humidity or temperature sensor and through a reference resistor, and periodically changing the direction of charging current through the humidity or temperature sensor in accordance with the charge/discharge cycle of the charging and discharging of said capacitor.
Specification