GB641555A - Humidity or dew point measuring apparatus - Google Patents

Abstract

641,555. Hydrostatic gauges. ILLINOIS TESTING LABORATORIES, Inc. April 2, 1947, No. 9029. Convention date, Sept. 30 1943. [Class 106 (ii)] [Also in Group XX] In an apparatus for measuring the dewpoint of gas samples wherein the pressure of the gas is successively lowered with resultant adiabatic cooling until a critical pressure is reached whereat no fog is formed on cooling (see Group XX), a pressure gauge is provided which enables a direct reading of the dew-point to be obtained. The gauge 133 comprises a tube 134 having a bore 134a containing, for example, mercury 140, the tube being curved around the periphery of a rotatable disc 135 which is mounted on a bracket 138 secured to a tube 139 which serves as the communication tube between the gas reservoir 81 and the tube 134 and also as the support for the complete assembly. The upper end of the tube 139 opens into a mercury trap 134b formed at the upper end of the tube 134, the arrangement being such that the bore 134a may be placed into communication with the tube 139 by tilting the instrument, without the mercury entering the tube 139, so that at the commencement of the test the pressure of the gas confined in the bore is that of the atmosphere. With such equal pressures on either side of the body of the mercury 140 the lower end of the mercury lies at the zero mark 143. The gas is then pumped into the reservoir to the desired maximum pressure and the rotatable dial 135, bearing a logarithmic scale of temperatures 136 is rotated until the graduation corresponding to the temperature of the gas in the reservoir is opposite the zero mark 143. The gas in the reservoir is then allowed to expand to atmospheric pressure in successive stages in a fog chamber, each stage being accompanied by a decrease in the pressure of the remaining gas and when the lowest pressure effective to produce fog is reached the position of the mercury corresponding to that lowest pressure indicates via a logarithmic pressurescale 136a the desired dew-point on the logarithmic temperature scale 136.