Patent GB-190321027-A (GB)
Title: Improvements in and relating to Electricity Meters.
Inventor: HAMILTON WILLIAM
Filed: 1903-09-30
Granted: 1904-09-29
Abstract: 21,027. Hamilton, W. Sept. 30. Quantity meters.-A meter has a metal armature immersed in mercury, in the fields of two or more pairs of pole-pieces, on one or more permanent magnets ; the current passes radially through the armature and mercury, between two of the polepieces, by which the armature is driven, while the other pairs of pole-pieces serve only to retard the armature magnetically. The armature may however be driven by more than one pair of pole-pieces. The magnets are bars or plates of rectangular section bent into circular or C-shaped forms, or as shown at n. In a simple form of meter with a disc armature, the pole-pieces are formed on two parallel flat plates, attached to the magnet poles, a ring being placed between the plates to retain the mercury ; crossed grooves in each plate leave four projecting pole-pieces of sector form. Otherwise the pole-pieces may be cylindrical pieces t, u carried directly on the magnets, or on iron plates p attached thereto ; such a pole-piece may be divided by an air-gap as shown, the end portion being fixed in the lower plate of the mercury chamber, while the body of the pole-piece is supported adjustably by a screw ring v or otherwise on the magnet, or on the extension plate p. By this adjustment, the meter constant can be varied. The constant may be otherwise varied by shunting the mercury bath or the whole meter by resistances. A steadying-resistance may be used in series with the mercury bath. The retarding pole-pieces may be conical, to increase their effect. In order to compensate for the increasing effect of fluid friction at high speeds, main-current coils w, x are placed on the driving or retarding pole-pieces, or on a soft iron bar which magnetically connects a driving pole-piece to a retarding pole-piece of like polarity, with intervening air-gaps. In either case, the coil acts to weaken the magnetic flux through a retarding pole-piece, while increasing that through a driving pole-piece. To adjust the compensation, the coils or their connections may be altered, or they may be shunted by resistances, or the air-gaps may be altered. In a meter having two C-shaped magnets, four pole-pieces, and two soft iron connecting bars, these parts may be clamped together by passing screws through the bars into a brass frame. The armature disc g is of copper, amalgamated at its edge and centre, but otherwise plated with platinum, or coated with non-conductive material. The mercury chamber may be formed by a fibre ring and two plates of non- magnetic metal, which are insulated from the mercury by thin discs of fibre ; a step bearing h for the lower end of the armature spindle serves as one electric connection, the other being a rod j inserted through the rim of the chamber. The top plate of the chamber may carry a short vertical tube, surrounding the spindle ; in order to close this tube, for transport of the meter, it is connected by an india-rubber tube to a ring on a lever, which is pressed up by a spring to hold the ring and india-rubber tube against an enlarged part of the spindle. The lever and ring are depressed by a screw with a milled head, when the meter is set up.