Patent GB-857917-A (GB)
Abstract: 857,917. Dynamometer instruments. ELLIOTT BROS. (LONDON) Ltd. Jan. 28, 1957 [Feb. 6, 1956], No. 3686/56..Class 37 A mounting means for the fixed coil of a dynamometer instrument comprises two limbs 3 in spaced parallel relationship, two opposed, inwardly directed lugs such as 2 for supporting the fixed coil, a pair of shoulders, such as 8, capable of supporting a locating or clamping element, a pair of grooves 9, capable of supporting a damping device or a further locating device and mounting means such as projections 10. The limbs 3 may be formed into a frame 1 having two outward projections 10 containing metal bushed coaxial bores 12. The frame may be cast or moulded from material known under the (Registered Trade Mark) "Mycalex". In a dynamometer instrument, Fig. 7, the fixed coil is retained by a strip 28 on either side of the frame 1. The moving coil 19 and the mirror 30 are mounted on a spindle 20a which is suspended by fine wires 20 between mountings 21, 22. The suspension may be clamped by a resilient strip 25 which urges a cylinder 25c, carried by the spindle 20a, against a recess in a member 25b, which is supported between the shoulders 7. The strip 25 is controlled by a cam 24 operated by a spindle pivoted in the top of frame 1. Fig. 8 shows a multiple element instrument in which each fixed coil 27 (only one shown) is mounted on a frame 1 comprising part of that shown in Fig. 1. Alternate frames are mounted at right angles on two pairs of rods 48 which pass through bores in the projections 10. One set of frames is rigidly fixed by nuts or collars 52. Provision is made for adjusting the two sets of frames by oversize or elliptical bores in the projections 10. The upper limb of all frames except the uppermost is omitted. The lower limb of all frames except the lowermost is replaced by a hexagonal locating element 42 having two parallel sides which are cemented in grooves 9, Fig. 1, and having a downward depending cylinder which engages recesses 8 formed in the shoulders 7 of the adjacent lower frame. The locating element 42 is provided with a coaxial bore and a radial slot to permit introduction of the suspension which consists of moving coils 19 suspended or pivoted so that each coil is at right angles to the appropriate fixed coil in the zero position. Damping. An air-vane damper 31 is cemented in the grooves 9 of Fig. 7 and the lowermost grooves 9 of Fig. 8 and comprises a member 32, Fig. 6, having a coaxial bore 34, parts of the walls of which are cut away to open into two chambers 33 in which air-vanes 40 rotate. The air-vanes 40 have stems 41 which are attached to the suspension. The chambers 33 are covered by plates 39 attached to the frame by lugs 39a, Fig. 7. Alternative damping by feedback to an auxiliary element may be employed. Screening. The instruments shown in Figs. 7, 8 are screened by a housing of high permeability alloy. Inter-element screens, Fig. 11 (not shown), take the form of a high permeability disc having a peripheral flange and a central depression which fits between the locating element 42 and the shoulders 7 of the frame 1. The screens have a coaxial bore and a radial slot to allow the suspension to be introduced. Alternative screens comprise an insulating body sandwiched between two metal discs.