Patent GB-1482705-A (GB)
Title: Electrical rotation transducers
IPC: H01F29/10
Filed: 1974-10-21
Abstract: 1482705 Angular displacement transducers HITACHI Ltd 21 Oct 1974 [19 Oct 1973 22 July 1974 24 July 1974] 45448/74 Heading G1N An electrical rotation transducer comprises a movable and a fixed magnetic core defining therebetween two gaps of predetermined width in respective magnetic circuits having a common central cylindrical magnetic leg portion, the cores being so arranged that relative rotation between them causes the common poleface area of one gap to increase and that of the other gap to diminish by an equal amount; a first coil surrounding the common magnetic leg portion and at least a second coil surrounding part of at least one magnetic circuit other than the common leg portion. An angular displacement transducer, Fig. 6, comprises a fixed core 1b having a centre limb 6b and two opposed arcuate limbs 12b, 13b joined by a circular base. A semicircular disc 2b is rotatably mounted with a thin friction disc, e.g. PTFE, on the fixed centre limb 6b. This embodiment may be modified to provide a centre limb integral with the movable core and extending into or through a bore in the fixed core, Figs. 11, (not shown) and 12. Another embodiment of an angular transducer includes a movable core 2a, Fig. 1, having a semicylindrical skirt of the same radius as the arcuate limbs 12a, 13a of the fixed core 1a. Alternatively, Fig. 10 the semi-cylindrical skirt embraces the fixed limbs 12e, 13e to provide radial gaps, the secondary windings 4e, 5e being arranged on a bar joining the fixed limbs 12e, 13e. To avoid errors due to tilting of the movable member under vibration, a fixed core 1f Fig. 12 has four arcuate limbs 16f, 16f', 26f, 26f' and the movable core 2f comprises oppositely extending flat quadrants. Secondary coils 4f, 4f' surrounding opposite fixed limbs 16f, 16f' are connected in series assisting. Any tilting of the movable core.2f causes equal and opposite changes in the widths of opposite gaps which, to a first approximation, result in complementary changes in the induced EMFs and thus no substantial change in their sum. Further series-connected secondary coils may surround the limbs 26f, 26f'. These will similary be compensated for tilt, but will respond to measurable angular displacement in a manner complementary to that of the coils 4f, 4f'. Compensation both for tilt and for axial shift of the movable member is provided by the embodiment of Fig. 15 comprising a fixed core of two arcuated portions 1g, lg' positioned by a non-magnetic member 19g, and arranged between a pair of semicircular discs joined by a central shaft to constitute a movable core 2g. Under tilting or axial shift, the sum of gap widths 9g, 9g' constituting a first gap remains unchanged, as does also the sum of gap widths 10g, 10g' constituting a second gap. If in any embodiment two secondary coils are arranged to undergo complementary changes in induced EMF in response to a displacement to be measured, these coils may be connected in series opposition, their resultant output being rectified. The datum point of a transducer may be shifted through a predetermined amount by providing secondary coils of unequal numbers of turns on respective magnetic circuits. For energizing the transducer an emitter-coupled Colpitts oscillator is disclosed, Fig. 22, (not shown) using the transducer primary winding (3) as a tuning inductor and having in its emitter feedback circuit a NTC resistor (RT) for compensation against thermal reduction in output amplitude.