Patent ID: 7087326

Claim:
A fuel cell system, comprising: a moisture sensor working to measure a moisture content of a measurement gas, said moisture sensor including (a) an electrochemical cell having a first electrode exposed to the measurement gas and a second electrode exposed to a reference gas, said electrochemical cell outputting an electrical energy arising from chemical reaction of the measurement gas with the reference gas, (b) a voltage detector working to measure a voltage appearing at said electrochemical cell, (c) a current detector working to measure a current produced by said electrochemical cell, and (d) a controller controlling at least one of the voltage and the current of said electrochemical cell, said controller determining the moisture content of the measurement gas using one of the voltage and the current and providing a signal indicative thereof; a fuel cell producing an electrical energy through chemical reaction between hydrogen and oxygen; a moisture controlling mechanism working to control a quantity of moisture within said fuel cell; and a system controller working to determine a moisture condition within said fuel cell using the signal outputted from said moisture sensor, said system controller actuating said moisture controlling mechanism to control the quantity of moisture within said fuel cell to a desired value based on the determined moisture condition, wherein the measurement gas and the reference gas are identical in kind with each other, and wherein said controller works to bring a potential difference between the first and second electrodes of said moisture sensor to a given potential difference and determines that the quantity of moisture within said fuel cell is excessive when the current produced by the electrochemical cell is smaller than a first preselected current value.