GB400651A - - Google Patents

Abstract

400,651. Current and pressure meters. DRYSDALE, C. V., Derek Corner, Kingsway, Hove, Sussex. April 28, 1932, No. 12252. [Class 37.] In permanent magnet measuring-instruments of either the moving coil or moving magnet type, the polepieces and any central core which may be required are made of a highly permeable ferro-magnetic material, such as a nickel-iron alloy, and graduated air gaps are employed in order to obtain any desired form or angular range of scale. Mathematical formulae for determining the form of the gap are given. One form of permanent magnet moving coil instrument, with polepieces 1, core 2 and coil 3, designed to give a logarithmic scale, is shown in Fig. 1. In an astatic instrument, Fig. 3, two flat D-shaped coils 5 are mounted on a spindle 4 to move in their own plane between the poles of a pair of permanent magnets 7. In another form, Fig. 5, the moving coil 8 is of sector shape, enabling deflections up to about 270‹ to be obtained. The application to a moving magnet instrument is shown in Fig. 7, the permanently magnetized cobalt steel or aluminium steel needle 9 being rotatably mounted between the poles of a ring 10 of nickel-iron alloy. By mounting the magnet obliquely on the spindle, the range of deflection may be extended to about 270‹. The instruments may be employed with spring control or with a variable magnetic control of the kind described in Specification 400,654.