GB191516112A - Improvements in and connected with Ohmmeters and like Electrical Measuring Instruments. - Google Patents

Abstract

16,112. Trent, H. E. Nov. 15. Electro-magnetic current meters; resistances, measuring.-A moving-coil instrument has two coils surrounding curved pole-pieces and opposing one another without other control except that of an auxiliary coil which neutralizes the effect of the restoring-coil in the initial position to prevent sticking; the coils have a long range of movement. In the ohm-meter shown in Fig. 3, permanent magnets 7, 8 have polepieces 3, 4 for the armature 2 of the usual dynamo, and pole-pieces 10, 11 for the pressure coil 25 and current coil 24 respectively, on either side of a pole-piece 9 of opposite polarity. The pole-piece 9 is shown separately in one form in Fig. 6; the slot 16 for the passage of the shaft 22 may be closed by a removable piece, or the pole-piece may be divided along the middle. The pole-piece 11 is in the form of a divided ring of uniform or tapering section, as shown in Figs. 11 and 12, and the pole-piece 10 is of hook-form with a circular or spiral edge, as shown in Fig. 10, and a projecting piece 20 for the auxiliary coil 26. In the modification shown in Fig. 15, the projection 34 of the lower pole-piece has a fixed auxiliary coil 35 to oppose the moving coil 25 in the initial position in place of the coil 26. In other modifications, (1) the coils 24, 25 are mounted on opposite sides of the shaft, and (2) they are mounted about a single pole-ring. An adjustable resistance 41 is included between the current coil 25 and the resistance 29 to be measured.