Patent GB-527087-A (GB)
Title: Improvements in or relating to induction type electricity integrating meters
IPC: G01R11/36
Filed: 1939-03-31
Abstract: 527,087. Supply meters. FERRANTI, Ltd., PRINCE, J., and WHITEHEAD, M. March 31, 1939, No. 10056. [Class 37] [Also in Group XXXV] An induction type meter is provided with an auxiliary motor consisting of a rotor and a pair of stator members energized by leakage flux set up in the three-limbed shunt core, the auxiliary motor being symmetrically disposed with respect . to the two shunt leakage flux paths associated with the core. A prepayment induction type meter for a two-part tariff system is shown in section in Fig. 2 and plan Fig. 3. The core of the shunt electromagnet has three separate parallel limbs held in relative position by two brass strips 4 at each end. A steel back plate 5 is attached to the top of the middle limb 3 and carries a tongue piece 6 at its lower end. The magnet is attached to a steel frame 7 by bolts 8 passing through the top and bottom of the two outer limbs. Attached to the tops of the two outer limbs is a circular steel plate 10 having a central hole and teeth projecting radially inwards. A second steel plate 13 with outwardly projecting teeth is attached to the top of the centre limb of the magnet with its teeth between the teeth of the ring 10 and with a small clearance. The plates 10, 13 form the stator of a synchronous motor which has a six-limbed rotor 14 permanently magnetized so that alternate limbs are of opposite polarity. Each limb has two teeth similar in size to the stator teeth, the teeth being arranged with respect to the stator teeth as described in Specification 477,835, [Group XXXV], so that the motor is self-starting. The rotor spindle 15 carries a pinion 18 which drives through intermediate gearing one sunwheel 19 of a differential gear, the other sunwheel 22 of which is geared to the meter disc 20. The planet-wheel 23 communicates the sum of the motions of the sun-wheels 19, 22 to one member of a second differential gear of which the other members are connected to a switch and coin mechanism. In a modification the shunt magnet is E-shaped and has the extremities of the outer limbs turned towards the middle limb, the extremity of the middle limb comprising two toothed convex cylindrical surfaces turned.towards the outer limbs and the extremities of the outer limbs comprising toothed concave surfaces separated from the convex surfaces by a small clearance. In a further modification one of the toothed stator members is separated by a block of magnetic material from an extremity of the middle limb of the E-shaped magnet whilst the other toothed stator member forms part of the back plate 5. In another construction, Fig. 10, the stator is formed of two arcuate portions 34, 35 of opposite polarities, the portion 35 being attached to the two outside magnet limbs 1, 2 and the portion 34 being attached to the top of the central limb. The rotor 37 is a toothed wheel of soft iron and has a starting-knob, since the motor is not self-starting. Where synchronism with the supply frequency is not essential, a Ferraris type motor may be employed. The auxiliary motor may alternatively be driven by the flux of the series electromagnet.