GB757211A - Improvements in electrical strain gauge load-measuring devices - Google Patents

Abstract

757,211. Resistance strain gauges. ELLIOTT BROS. (LONDON), Ltd. Oct. 6, 1954 [July 6, 1953], No. 18719/53. Class 40(1) A load measuring device comprises an elastic element, arranged to be stressed proportionately to a force or displacement to which is firmly fixed a set of resistance strain gauges of wire of between .004 and .015 in. diameter adapted to form arms of a D.C. or A.C. fed Wheatstone bridge wherein the gauges are enclosed in a chamber filled with liquid, e.g. oil, with good heat transmission properties. The elastic member may be a solid cylinder 1 of high tensile steel on which are shrunk end rings 2 of mild steel. On the outside plane of each ring a peripheral rabbet 3 is formed which locates annular brass end plate 4 hermetically sealed to the ring 2 and to cylindrical wall 11. Active strain gauges 9, 10 are wound in interleaving zig-zag fashion between two sets of equally spaced pins 7, 8a; 8, 7a respectively. Temperature compensating gauges 6, 6a transverse to the direction of stress are wound round the cylinder ends as shown or on top of the active gauges. The resistance wire is insulated by an enamel or silk coating or both and bonded to cylinder 1 by an oil resistant adhesive, e.g. a resin such as Araldite (Registered Trade Mark), vitreous enamel or low melting glass. The input and output terminals of the bridge are connected to conductors 12 hermitically sealed through and insulated from wall 11, only the output terminals being shown in Fig. 2. Pins 7, 7a, 8, 8a which are of anodized aluminium or insulating material may be removed after the bonding process. Alternatively, they may form part of a removable jig. The bridge output may be amplified or fed directly to an industrial indicating and recording instrument. The gauges may be constituted by a single wire of .01 in. diameter to which appropriate connections are soldered.