GB830077A - Improvements in or relating to moisture meters - Google Patents

Abstract

830,077. Electric indicating systems. ZURCHER PAPIER.FABRIK AN DER SIHL. Dec. 21, 1955 [Dec. 23, 1954; Jan. 7, 1955], No. 36682/55. Class 40 (1). [Also in Group XXXVI] A moisture meter comprises a hydroscopic element whose resistance is measured and which is made from a viscous mixture of a solution of a hydroscopic salt and at least one finely divided or granulated electrically non-conducting filler which is insoluble in the solution. A construction of meter is shown in Fig. 3 in which the hyposcopic layer (for construction of which see below) is applied by brushing to a disc-shaped insulating support 15a which may consist of glass quartz or porcelain and which carries electrodes 16, 17 of precious metal making contact with the hygroscopic layer. A similar layer 18a for comparison purposes is situated on the upper side of disc 15, which is supported by elastically yielding sealing rings 33, 34 in a metal block 13a so that a hollow compartment 14a is formed below the lower layer 18 and a hermetically sealed compartment 35 above layer 18a. The upper compartment contains a humidity buffer 37, e.g. of potassium carbonate contained in a vessel 36 and held in chamber 35 by leaf springs. Below the lower hygroscopic layer is a direct filter 50 of powdered quartz mixed with paraffin and toluol and sprayed on a wire mesh, and a perforated disc provided for mechanical protection. The substance 11 under test is allowed to stand on metal base 11 to take up the temperature of the base and the gauge is then positioned on the substance. Elements 18, 18a form opposite arms of an A.C. bridge and unbalance is indicated by meter 52 connected to a slider on resistor 51 forming two arms of the bridge. In the arrangement of Fig. 1 (not shown), a single hygroscopic element is used and cavities containing humidity buffers are provided in the base-plate. An arrangement is also described (Figs. 4 and 5, not shown) for measuring the humidity of air in which a disc-shaped member containing the sensitive elements is attached at the edge to a handle, one of the sensitive elements being sealed in a rear compartment with a humidity buffer for by soaking felt or blotting paper in a calcium chloride solution. Preparation of hygroscopic layer.-The layer consists of a solution of a hygroscopic salt or salts, e.g. zinc chloride, lithium chloride in admixture with a finely divided or granulated inert filler, e.g. barium sulphate titanium dioxide powdered quartz, a powdered synthetic resin insoluble in water or a mixture of two or more such substances. The mixture may also contain thickening means such as gelatine or a synthetic resin or resins soluble in water and or a wetting agent or agents.