GB804731A - A variable resistor - Google Patents

Abstract

804,731. Variable resistances. MONTAGA, J. D., and CHIDZEY, R. L. Nov. 15, 1955 [Nov. 22, 1954], No. 33802/54. Class 37. [Also in Group XXXVIII] A variable resistor comprises a tube of partially conducting material which contains a column of mercury, electrical connection being made to the tube at one end spaced apart from the mercury and to the mercury itself so that as the column of mercury is moved along the tube the resistance between the two terminals varies. In the Figure the tube 1 of U-form with the mercury 2 constitutes a manometer, the tube is of polyvinyl chloride loaded with conductive carbon black having a resistance of about 80 ohms per inch length of tube or alternatively the tube may be constructed of the conductive plastic known by the Trade Mark " Markite ". Connections are made to the tube at the ends 3, 4 and to the mercury at position 5 if required by passing a conductor into the mercury through the wall or one limb of the tube. Pressure applied to one limb of the U-tube causes variation in the ratio of the resistances between the mercury and connections 3, 4, thus causing an out-ofbalance of the Whetstone bridge of which these two resistances form an arm, the volt meter 9 deflecting accordingly. The mercury may be that of a thermometer (see Group XXXVIII), the circuit then indicating temperature changes.