Patent GB-998720-A (GB)
Title: Position transducers
IPC: G08C19/06
Filed: 1961-12-11
Abstract: 998,720. Measuring displacement electrically. R.E. CLAFLIN. Dec. 11, 1961 [Dec. 12, 1960], No. 44211/61. Heading G1N. [Also in Divisions G3 and H1] Apparatus for measuring linear or angular displacement comprises a closed magnetic loop and an armature associated with an energized winding, which interconnects opposite sides of the loop, the flux from the armature dividing into two paths through the loop is a proportion determined by the position of the armature and measured by voltages induced in individual coils coupling with the two paths, thereby giving an indication of the position of the armature relative to the loop. In one embodiment (Fig. 1), lateral movement in the arrowed direction of a core 19 carrying an A.C.- energized winding 18, straddling sections 12, 14 of a continuous core 10, causes alterations in the flux division between paths 36, 38, and hence differences in the voltages induced in coils 20, 22 joined in opposition to a voltmeter 34. The transducer produces a substantially linear output, except at the ends, and the cores 10, 19 may be shaped to extend the linearity range. In a modification (Fig. 2), the armature 19 is limited to the core 10 by a fixed portion 40 which carries the energizing winding 18. The position of the armature 19 may be determined by an automatically balanced arrangement (Fig. 2a) comprising an auxiliary winding 44 on the core part 42, linking the main core 10 to the portion 40, shunted by a potentiometer 48, the potential between the potentiometer slider 50 and the centre tap 46 of the winding 44 being compard as an amplifier 52 with the output from measuring windings 20, 22, any difference being removed by a motor 54 driving the potentiometer slider 50, the position of the slider at balance being linearly related to the displacements of the armature 19. Variations in total flux and compensated by comparing the voltage induced in coil 44 with a fixed proportion of the supply voltage 32 in an amplifier 60 (Fig. 2b), any difference energizing a motor 62 linked to an autotransformer 66 controlling the voltage to coil 18. A linear displacement transducer adapted for laminated construction using high permeability foil or tape comprises a core 19b (Figs. 6, 7) mounted on a slide 74 which is movable along guide member 76 fastened by arms 78, 80 over section 14b of the core 10b which urge the core 19b against section 12b and pedestal 40b. Core ends 21b, 23b may be provided with nylon caps. The core 10b may be made continuous by winding magnetic tape round a former, or separate end sections 24b, 26b may be used, which may be circular as 24b or semi-circular as 26b. The linear displacement transducer of Fig. 2 is adapted to measure angular displacement by making the cores 12, 40 curved (Figs. 4, 8 not shown) to allow for angular rotation of core 19. In an embodiment using the principle of Fig. 1 for measuring angular displacement (Fig. 10), the sections 12d, 14d, are almost complete circles, joined by linear sections 24d, 26d. The armature 19d comprises end sections 100, 102 joined by section 104 which is aligned with the axis of the end sections. A shaft 106 is journelled in a non-magnetic Spider 110 at each end. Energized coil 18d is wound on a tabular former 118 with the compensating coil 44d. The sections 12d, 14d may follow any other desired contour. Thus,to measure angles greater than 360 degrees, sections 12d, 14d are formed as multiple turn helices, the ends of the armature 19d contacting the outer peripheries of sections 12d, 14d. Transducers as above may constitute the transmitter and receiver of a displacement measuring system.