GB611730A - Improvements in or relating to dew-point indicators - Google Patents

Abstract

611,730. Photo-electric apparatus for indicating dew-points. CLIFFORD, G. E., and AIR CONTROL INSTALLATIONS, Ltd. Nov. 11, 1946, No. 29983/45. [Class 40 (iii)] [Also in Group XX] In a dew-point indicator, of the kind in which a light-beam falls on a photo-electric cell after reflection from a cooled mirror surface exposed to the atmosphere under test, the light beam is subjected to two such reflections. As shown, Fig. 1, the gas under test is admitted to casing 70 through inlet 71 and leaves through outlet 72. The trapezoidal shaped vessel 73, adapted to contain heating or cooling media, is provided with inlet and outlet connections 75 and external reflecting surfaces 74. In side-tube 76, a light beam from source 77 passes through focusing lens 78 and is reflected in turn from the surface 74, the auxiliary mirror 80 in sidetube 79 and the second reflecting surface 74, to the photo-electric cell 82 in side-tube 81. Thermometers 83, 84 measure the gas and dew point temperature respectively. The indicating circuit, Fig. 2, comprises the triode 52 which operates relay 55, subject to the control of the cell 82 connected between the grid 53 and cathode 51 in series with the battery 50. The triode is normally biassed to cut-off by adjustment of the resistor 54 when there is no deposition of dew in the surfaces 74. Two forms of the vessel 73 are described to permit the use of either ether or brine as the coolant and provision is made for raising the vessel temperature by the passage of a heated liquid through an internally mounted U-tube in the case where either is employed.