GB548105A - Improved electro-magnetic measuring apparatus - Google Patents

Abstract

548,105. Magnetic and inductance tests. TAIT, W. H. July 22, 1941, No. 9254. [Class 37] Apparatus for the measurement of pressures or small movements such as those occurring in structures under load comprises two U-shaped cores a, b, Fig. 1, arranged with their open ends facing one another, the cores carrying respectively a primary coil c and a secondary coil e and one core being fixed while the other receives the movement to be measured. The primary coil c is fed from a mains transformer d, if necessary through means for maintaining the voltage constant. The secondary winding e is connected through a rectifier f to a galvanometer g. Relative movement between the cores a, b varies the magnetic linkage and so modifies the E.M.F. induced in the secondary coil. An opposing E.M.F. may be included in the secondary circuit in order to control the range and utilise the whole scale of the galvanometer. This may be a steady E.M.F. produced by a second measuring unit identical with that shown in Fig. 1 reversely connected, or the backing-off E.M.F. may be provided by an indentical unit to the forward acting unit with the two moving cores so arranged that as one increases the linkage in its magnetic circuit the other decreases its linkage. In a modification, Fig. 4, a stationary backing-off unit comprises a U-shaped core a<1> facing a similar core b<1>. The core a<1> carries a primary winding c<1>, while the core bl carries a secondary winding l<4> connected with the main secondary winding e through rectifiers f<1>, f<2> in opposition to the measuring instrument g. On the other limb of the core b<1> is a secondary winding e5 connected in opposition to the winding e, and across the windings e<4>, e<5> are connected variable resistances r<1>, r<2> adjusted to give optimum proportions of alternating and direct current. In another arrangement, Fig. 5, there are two fixed cores b<2>, b<3> and two moving cores a2, a<3> fastened to a rod h mounted on two diaphragms i so that its movement is maintained parallel. The cores a<2>, a<3> have a common primary a5. The fixed core b<2> has a secondary winding e2, while the fixed core b<3> of the backing-off unit has secondary windings l<4>, l<5> shunted by variable resistances r<1>, r2. Specification 502,500 is referred to.