Patent GB-452134-A (GB)
Title: Improvements in measurement apparatus
IPC: G01R13/00
Filed: 1934-11-15
Abstract: 452,134. Current, pressure, power, and supply meters. CHILOWSKY, C., 15, Rue du Lunain, Paris. Nov. 15, 1934, Nos. 32943 and 32944. Void [Abridged as open to inspection under Sect. 91 of the Acts, May 16, 1935]. [Class 37] In an electric measuring instrument having movable parts mounted on a spindle with two pivots, the weight of these parts is balanced,either wholly or in part, by immersing them in a liquid. To avoid errors due to thermal effects, the parts to be balanced and the balancing members are preferably made of the same materials, or materials having the same coefficient of expansion. The mean density of the movable element is preferably equal to that of the liquid, and the centres of gravity and of buoyancy may be made to coincide, by employing floats. If desired, parts such as the indicating pointer may be balanced by means of tungsten wires wound on one side or the other of the axis of the movable element. The liquid may comprise a weak solution of soda or other alkali, the casing being of ebonite, but where the movable element includes windings, halogenated hydrocarbons, such as carbon tetrachloride, trichlorbenzene and brombenzene may be used, the casing being then made of a plastic material, such as cellulose-acetate, urea condensation products or polystyrol. An ammeter having a moving coil 1 and a fixed permanet magnet 6 is shown in Fig. 1, the coil being provided with floats 2, 2<1> fixed to the pivot pins 3, 3<1> and the needle 4 being balanced by a counterweight 5 of the same material as the needle. The needle may be arranged to have the same density as the liquid by making it in the form of a fluid-tight tube. The whole of the apparatus is immersed in liquid in a casing 8 of plastic material, the cover 8<1> being made of a plastic transparent material. The casing may be mounted in an outer casing 9 of metal, with an outer transparent cover 10. In a modification, Fig. 3 (not shown), the coil is arranged eccentrically to the spindle and is balanced by the needle, the spindle being made in the form of a hollow float. In another modification, Fig. 4 (not shown), the movable element includes two flat frames each in the shape of a segment of a circle, the frames, which act as floats, being rigidly assembled together and provided with coils on their periphery. In another form, Fig. 6, the movable element comprises a spindle 18 acting as a float, a needle 4 and soft iron piece 27, and rotates inside a stationary coil 29 having a stationary polepiece 28. In the wattmeter shown in Fig. 8, the spindle 20 carries floats 30, 31 and a voltage winding 32, which rotates inside a stationary current winding 33. The fixed elements, such as the coils in the case of a moving iron instrument, or the magnets in the case of a moving coil instrument, may be mounted outside the casing. In the power meter shown in Fig. 11, the spindle carries floats 44 and gears with toothed wheels 47, 48, each of which may be provided with floats. The movement of the disc may be damped by the viscosity of the liquid, the disc moving between blades 45, the distance between which is controlled by bimetallic elements 46 to compensate for changes in viscosity due to temperature variations. In a modification, Fig. 14 (not shown), the blades are carried by bellows partly filled with a liquid, e.g. ammonia solution, producing a vapour the tension of which varies with the temperature. The braking action of the liquid may be supplemented by magnetic braking devices.