Patent GB-828820-A (GB)
Title: Improvements in or relating to electrical resistance strain wire transducer
Inventor: STATHAM LOUIS D
IPC: G01P15/12
Filed: 1956-08-10
Abstract: 828,820. Resistance strain gauge devices. STATHAM LABORATORIES Inc. Aug. 10, 1956, No. 24580/56. Class 40 (1). A resistance strain wire transducer comprises at least one pair of strain wires, one end of the first wire of the, or each, pair being attached to a member which is movable, in response to variations of the physical variable to be measured, relative to the point of attachment of one end of the second wire, the other ends of both wires being attached to a resilient common point, so that a displacement of the movable member causes an increase in tension in one wire and a decrease in tension in the other. In the pressure gauge of Fig. 1, a diaphragm 5 is attached to one end of an axially movable rod 10, the other end of which is fitted with a cylindrical spacer 19 carrying an insulated pin 37 to which one end of a tensioned strain wire 51 is attached, the other end of the wire being soldered to a hook 49 on the free end of a leaf-spring 48 which is welded at its other end to a terminal 46 insulatedly brazed into a slot 44 in a rigid member 16. A second, preferably identical, strain wire 50 extends between the hook 49 and a pin 39 in one leg of an H-shaped milled block 26 which is attached to the member 16 and serves to regulate the tensions in the wires 50, 51, under the control of an adjusting-screw 33. A second pair of strain wires (not shown) identical with 50, 51, is disposed between a pin opposite pin 39 in the block 26, a hook on a second leaf-spring coplanar with spring 48, and a pin diametrically opposite pin 37 in spacer 19. Displacement of the diaphragm 5 due to the imposition thereon of fluid pressure via a bore 8 causes the tension in the wire 51 and the deflection of the spring 48 to decrease, and the tension in the wire 50 to increase ; similar variations occur in the second pair of wires. Both pairs of wires are connected to form a Wheatstone bridge arrangement, the variation in the output of which is proportional to the sum of the changes in strain in the wires. If one pair of strain wires only is used, two other resistors are employed to complete the bridge. Fig. 11 shows the transducer adapted for use as as accelerometer in which the end of the rod 10 remote from the spacer 19 is attached to the central disc 64 of a cylindrical weight 56, to each end of which is screwed a circular spring 58 or 59 which is also secured to the body of the device, which is filled with a non-conductive liquid as far as a diaphragm 72 which is clamped in a fluid-tight manner between fittings 68 and 76. The imposition of an accelerating force in either sense along the longitudinal axis of the device will displace the weight 56 and the rod 10 to vary the strains in the wires 50, 51. In the device depicted in Fig. 13, angular acceleration of the liquid-filled cylindrical case 79 of the device causes a relative angular displacement in a counter-direction of a centrally pivoted paddle 113, which increases the tension in one of two strain wire loops 130, 131, and decreases the tension in the other; these effects are duplicated in loops 132, 133. The loops 130, 131 are wound between a common pin 127<SP>1</SP>, insulatedly mounted on a block 126 attached by a leafspring 125 to a rigid bracket 124, and pins 129 and 129<SP>1</SP>, respectively, which are located on the paddle 113 on opposite sides of its pivotal axis. The paddle 113, which may be made of aluminium, magnesium, plastic, &c., extends diametrically of the case 79 and comprises two axially aligned cylinders 114 (Fig. 17) whose outer ends are sealed and whose inner ends are threaded into an oblong mount, to one side of which is centrally screwed a V-shaped spring 119 which, when secured to brackets 95, 95a, holds the paddle in suspension pivoted about the longitudinal axis of the case 79. The tensions to which the strain wires may be subjected, and the comparative elastic properties of wires and springs, are discussed in the Specification.