Patent GB-191109077-A (GB)
Title: Improvements relating to Electrostatic Measuring Instruments.
Inventor: ADDENBROOKE GEORGE LEONARD
Filed: 1911-04-12
Granted: 1912-03-14
Abstract: 9077. Addenbrooke, G. L. April 12. Electrostatic meters; vibration-dampers.-An electrostatic ammeter, volt-meter, or wattmeter has fixed field plates carried by platforms 5, 6, which are adjusted to be horizontal by use of temporary and permanent levels. In order to adjust the lower platform 6, a base-plate 1, Fig. 1, is levelled by screws 2, and levels are placed at right-angles on the lower set of field plates 4, and nuts 7 supporting the platform adjusted. These levels are then removed, and two other levels are secured permanently to the platform 6 and adjusted to give an horizontal indication. The upper field plates are then lowered into contact with the lower field plates, and other levels are secured to the upper platform 5 and adjusted. Adjustment of the electrical zero may be effected by tilting the platforms by means of a screw 48 with a milled head 49, the platforms being kept parallel by one or more screws 51. The segmental field plates in each set are secured by screws 12, Fig. 5, to an insulating-disk 11, which is provided with a groove 13 to receive the screws 12, and also the leads connecting the plates, this groove being afterwards filled up with paraffin wax. The plates may be secured to the disks bv cement. The plates may be made in any shape by cutting a disk secured to the insulating-disk. The faces of the plates are ground to a smooth surface. In addition to the supporting-nuts 7, locking-nuts may be provided above the platforms. Leads are secured in radial holes in the plates. Four or eight segments may be used in each set. The levelling- screws 2 may be provided on the rods 3. A flat mica needle 23 with two or more arms is coated with gold or other conducting-material, and is mounted on a shaft 24 with a mirror 25. The shaft is suspended by a narrow strip of silver 26 secured at its upper end to a rod 27, which passes loosely through an insulating-cap 28 supported on a cover 8, and has an adjusting-nut 29. On the top of the rod 27, a disk 30 is secured by a nut 31. Two rods 32, 33 pass through the cap 28, one rod 32 being screwed into the disk 30, and the other rod passing loosely through the disk and being secured by a nut 34. Springs 36 on the rods bear against the cap 28 and hold the rod 27 in position. On the lower end of the rod 33, two plates are secured, having knife-edges between which the supporting-strip 26 is held. The suspension may be adjusted vertically by means of the nut 29. The torsional elasticity of the strip may be varied by means of the nut 34, which varies the length of the strip below the lower knife-edge. Screws 43 are provided for centring the needle. On the lower end of the shaft 24 a damping- disk 45 is secured by means of a hook or otherwise, the disk hanging between two plates 46 carried on the rods 3. By adjusting the position of the plates, the damping resistance of the film of air between the plates and the disk can be varied. Several needles may be mounted on a common shaft, each needle moving in a separate set of field plates. In the arrangement shown in Fig. 6, two needles 53 insulated from each other are used, the upper needle being connected electrically with the suspension strip 26, and the lower needle connected with a strip 54 secured to the upper end 55 of a milled head 56 projecting through the base 1. In order to adjust the needle to its zero position, the needle is lowered until it is almost resting on the lower plates, and the milled head 56 rotated to bring the needle to its zero position relativelv to the segments. The needle is then lowered on to the plates and the instrument may be moved until the spot of light from the mirror is at the desired position on the scale, and the needle is then raised and adjusted for zero by the milled heads 31, 56. In a modification, the needle may be located between two disks of hard paraffin, or other material of high specific inducting capacity. According to the Provisional Specification, an F-shaped support for the suspension may be used, and the strip adjusted by means of a clip.