Abstract: An apparatus is provided for detecting the quantity of a specific gas hereinafter simply called "gas" in a carrier gas when water vapor is present. The gas and the carrier gas are passed through a whistle chamber which produces a resonating frequency. The resonant frequency changes as a function of the fraction of the gas, temperature and water vapor. An output signal is produced which is a function of the resonant frequency. A correction device senses water vapor and temperature and produces an output signal which is a function of the water vapor and the temperature. A receiving means receives the output signals and produces a resultant signal which is a function of only the fraction of the gas.

Abstract: Method and apparatus for controlling the amount of outside air introduced into a given space being ventilated as a function of the oxygen content of the air in the space to minimize the energy expended in heating or cooling air flowing through the space while maintaining the oxygen content of the air above that required for the well-being of humans occupying said space. A fuel cell produces an electric current the magnitude of which is a function of the partial pressure of the oxygen present in the air surrounding the fuel cell. The output of the fuel cell is applied to a control circuit which applies control signals to the motor control circuit of a damper motor to admit outside air when the partial pressure of the oxygen in the occupied space falls to a predetermined minimum level and to exclude outside air and to recirculate return air when the partial pressure of the oxygen in the space rises to a certain maximum level.