Patent GB-245707-A (GB)
Title: Improvements relating to direct-current ampere-hour meters
IPC: G01R11/30
Filed: 1924-10-18
Abstract: 245,707. Wall, G., and Metropolitan- Vickers Electrical Co., Ltd. Oct. 18, 1924. Mercury motor meters; temperature errors, compensating for.-On the cover of an insulated mercury trough are supported as a single unit the rotor disc with its supporting structure and the magnet or magnets so that these parts may be removed from the mercury without disturbing their relative positions. In the construction shown in Fig. 2, a permanent magnet 20 is provided with four pole-pieces 21 - - 24 secured to the magnet by screws and to a brass base-plate 26 by making them a force fit. The pole-piece 21, below the disc 36, and the polepiece 24. above the disc 36, are secured to one pole of the magnet 20 by screws 25 as shown in Fig. 5. Similarly the pole-pieces 22, 23 are secured to the other pole. The two air-gaps in which the disc 36 rotates are therefore in parallel. Each of the pole faces of the pole-pieces 21, 22, 23, 24 is provided with fringe pieces 27 of material of which the magnetic permeability decreases with a rise of temperature such for example, as is described in Specification 30297/10. The lower pivot bearing 35<A> is carried by a brass plate 35 secured to the lower pole-pieces 21, 22. The upper bearing is carried by a plate 29 which is supported by pillars 28 from the base-plate 26. This bearing consists of a bush 30 in which slides a plunger 33 pressed down by a leaf spring 34 and forming an abutment for the upper end of the spindle 32. A collar 39 sliding over a bush 38<A> secured to the base-plate 26 has its upper end faced to provide a mercury seal with a collar 37 when raised by a lever (not shown), at the same time lifting the spindle 32 from its lower bearing 35<A>. In order to prevent the mercury from attacking the base-plate 26. this is covered on its lower side with a mercury-resisting washer 40 and another thin sealing-washer 41. The mercury-container 42, shown detached, consists of moulded insulating material and is shaped to conform internally with the parts of the meter below the base-plate 26, in order to economize mercury. Contacts 43 for leading the current in and out are moulded into the container. The container 42 is secured to the meter assembly by screws passing through holes 47 in the base plate 26 into tapped holes 48 in the mercury container 42. In the modified construction shown in Fig. 6, a brass base-plate 26 has secured to it by setscrews 50 two C-shaped cobalt steel permanent magnets 51 having pole fringes of material of negative temperature co-efficient of permeability. A bridge 35 is carried by a pillar 54, secured to the base-plate 26, and a piece of insulating- material secured to the base-plate 26 between the two magnets 51. The bridge-piece 35 carries the lower bearing 35<A>, the upper bearing 30 being carried by a bridge 29 supported by two pillars attached to the base-plate 26. The mercury container 42 is moulded of insulating material and shaped internally to conform to the contour of the parts below the base-plate 26, and is secured to the base-plate 26 by screws. One or both of the magnets 51 are adjustable about the securing screws 50 so as to change the radial distance of their pole-pieces from the spindle, for adjusting the rate of the meter.