Patent ID: 7781118

Claim:
A fuel cell stack comprising: a fuel cell having an inlet, a flow field in fluid communication with said inlet and an outlet in fluid communication with said flow field; a vaporized water source in fluid communication with said inlet; a differential pressure transducer repeatedly measuring a differential pressure across said flow field and generating a set of differential pressure signals; a computer comprising a collection of the set of differential pressure signals measured during operation of the fuel cell; and the computer further comprising a controller in communication with said differential pressure transducer, said controller is configured to execute logic for determining a root-mean-square value from only said collection of the set of differential pressure signals and control circuitry for controlling said vaporized water source in response to the root-mean-square value, wherein the fuel cell stack attains a steady state in less than about 100 seconds at a sampling of about 10 Hz or greater.