GB737658A - Improvements in apparatus embodying a temperature-controlled element - Google Patents

Abstract

737,658. Dew point hygrometers. ELLIOTT BROS. (LONDON), Ltd. April 13, 1953 [Feb. 26, 1952], No. 5065/52. Class 97 (3). [Also in Groups XI and XL (b)] In a dew point hygrometer embodying a temperature-controlled element, the latter is connected to a heat sink by one or more members composed of such a material and having such a cross-sectional area that they will restrict the heat flow from the element to the heat sink while permitting this flow to proceed. at a relatively rapid rate, and means is provided for electrically generating heat within the member or members for supplying heat to the element, when desired, without disconnecting it or them from the heat sink. The temperature controlled element of the dew point meter shown is a copper disc 1 of low thermal capacity covered with a platinum foil 2 having a polished surface, and secured to rods 3 of small cross-section and length and composed of a material such as tungsten having poor electrical conductivity but better thermal conductivity. These rods are connected to copper bars 4 which are clamped together at 5 and have their lower ends, when in use, immersed in carbon dioxide snow in a vessel 6. These bars form the secondary winding of a transformer 8 having a ring-shaped core 7 and a primary winding 9. In use, the lower ends of bars 4 are immersed in the carbon dioxide snow and a gas whose dew-point is to be determined is caused to flow across the polished surface 2. When dew is deposited on this surface, the temperature is determined as by making use of the thermal electromotive force generated at the junction between the surfaces 1, 2. The temperature of surface 2 may then be raised by supplying alternating current to the winding 9 of the transformer whereby the bars 4 are strongly heated. A deposit of dew may be detected by illuminating the polished surface 2 with a light beam focused on a mirror parallel to this surface. When no dew is on the surface this mirror reflects all the light from the surface to a photoelectric cell, but the scattering of the light which occurs when the dew is deposited causes some of the light to fall on a photo-electric cell disposed behind the mirror. In another method, light from the lamp passes through a diaphragm and is reflected by the surface onto another diaphragm arranged to prevent such light from falling on a photo-electric cell arranged therebehind when the temperature is above the dew point but to allow the passage of such light when dew is deposited (see Group XL (b)). The disc 1 and foil 2 may be enclosed in a housing having a transparent cover and a gas inlet and outlet, and the rods 3 may be replaced by a U-shaped element which is clamped to the upper ends of the bars 4 (Fig. 2, not shown).