APPARATUS AND METHOD FOR MEASURING THE AIR FLOW COMPONENT AND WATER VAPOR COMPONENT OF AIR/WATER VAPOR STREAMS FLOWING UNDER VACUUM

The inventive method for measuring the mass of the gas component and the mass of the water vapor component of a gas/water vapor source stream flowing in a conduit under reduced pressure comprises storing a correlation of relative saturation of water in said gas and the output electrical signal of a relative humidity sensor. Next, a correlation of the flow rate of the gas component of a flowing gas/water vapor reference stream and the output electrical signal of a temperature-compensated flow sensor as a function of water vapor density is stored. A correlation of maximum water vapor saturation in the gas as a function of temperature also is stored. An electrical signal of a temperature sensor in contact with said source stream then is generated. An output electrical signal of a relative humidity sensor in contact with said source stream also is generated. An output electrical signal of a temperature-compensated flow sensor in contact with said source stream further is generated. The relative humidity output signal is compared with said stored relative saturation correlation to derive a relative saturation value which value is multiplied by the maximum water vapor saturation correlation for the temperature determined from the temperature sensor signal in order to derive the mass density of the water vapor component of said source stream Finally, the flow sensor signal is compared with said stored gas flow rate correlation at derived water vapor mass density to derive the flow rate of the gas component of said source stream. Also disclosed is the apparatus for carrying out the method. Also disclosed is a method and apparatus to incorporate a pressure sensor along with these three primary sensors to provide other correlations to provide redundancy to the relative humidity sensor in the event of its failure and to provide indications of the existence of water mist contamination of the source stream.