GB417376A - Improvements in inductance coils - Google Patents

Abstract

417,376. Inductances. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, TURNER, H. C., and POLGREEN, G. R., c/o Salford Electrical Instruments, Ltd., Silk Street, Salford, SMITH, C. G., and SMYTH, C. N., c /o General Electric Co., Wembley, Middlesex. Feb. 1, 1933, No. 24137/34. Divided out of 417,378. [Class 37.] The winding of a variable inductance is arranged on a part of the core which is in the form of a bar arranged within and extending across a hole in the second part of the core and rotatable to vary the reluctance of the magnetic circuit. In the construction shown in Fig. 1, the core part a has an oval hole, the diameter D1 being greater than D2. The core part c carrying the winding is placed within the hole in the part a so as to be rotatable about a central axis. As the part c is rotated, the length of the air gap between the two parts is varied, thereby varying the reluctance of the magnetic circuit. Alternatively, the hole in the core part a may be circular as shown in Fig. 2, the outer perimeter being of any shape other than a circle concentric with the hole. The inner core part may be shaped as shown at f or g and may have its edges at right-angles to its face or bevelled as shown to prevent binding, the edges of the hole being correspondingly bevelled. When the coil is enclosed in a screen, as shown in Fig. 3, the screen is formed in two relatively rotatable parts 5, 6, the part 5 carrying the outer part 1 of the core and the part 6 carrying the inner part 2. The inductance is adjusted by rotating the screen part 5 relatively to the part 6. The parts may then be fixed if a coil of fixed inductance is required. The core may be a dust core pressed or stamped in dies, or it may be built up from laminations. The invention is applicable to filter coils, telephone loading coils, and tuning coils for broadcast receivers.