Patent GB-537743-A (GB)
Title: Improvements in or relating to indicating meters particularly for radio navigationalpurposes
IPC: G01R11/48
Filed: 1940-01-03
Abstract: 537,743. Phase-difference measurements. STANDARD TELEPHONES & CABLES, Ltd., SCAIFE, F. N., NALDER BROS. & THOMPSON, Ltd., and LIPMAN, C. L. Jan. 3, 1940, No. 169. [Class 37] In an instrument for indicating the resultant of two or more electrical vector quantities of the type in which the moving system comprises six or more vanes of magnetic material mounted on a common axis and adapted to rotate in the field of one or more fixed field coils, the vanes are grouped in pairs to form three or more separate magnetic systems each magnetized by a fixed annular reference coil, each of two or more of the reference coils which are adapted to carry one reference current being separated from its next adjacent one along the common axis by a reference coil adapted to carry another reference current. As shown, the moving system comprises four separate magnetic systems 1, 2, 3, 4 mounted coaxially on a shaft S and separated by non-magnetic spacers N. Each magnetic system comprises a pair of quadrantal plates PI, P1<1>, P2, P2<1>, P3, P3<1>, P4, P4<1> of thin soft iron mounted one near each end of a rod R1, R2, R3, R4 of magnetic material. The plates of each pair are spaced at 180 degrees radial separation and the consecutive magnetic systems are spaced at 90 degrees radial separation relative to one another. The four magnetic systems are energized by stationary concentric coils C1, C2, C3, C4, of which the coils C<1>, C3 are connected in series across terminals F1, F1<1>, with or without a resistance Z1, and are supplied with a reference current of frequency f1. Similarly the coils C2, C4 are connected in series across terminals F2, F2<1> and are supplied with a reference current of frequency f2. The moving system is situated in the field of an exciting coil E connected to terminals E1, which coil may be wound in two sections on opposite sides of the spindle S. The moving system is damped by an eddy current brake comprising an aluminium disc D rotating between the poles of one or more permanent magnets M, a magnetic screen L being interposed between the magnets and the plates of the moving system. The coils C1, C3 carrying a reference current of one frequency, are astatic with regard to the field of the coil C2, which carries a current of a different frequency. Similarly the coils C2, C4 are astatic with regard to the coil C3. For reading the bearing of a distant radio transmitting station the instrument operates in conjunction with the receiver amplifier and a pair of loops rigidly fixed at right angles to each other. A signal is modulated at one frequency in one loop and at a second frequency in the second loop. The two outputs together with a signal from a vertical " sense " aerial are combined, amplified, detested, and the output fed to the exciting coil. The two reference coils are each fed with one of the modulation frequencies, the fields set up being of equal strength, the pointer taking up a position making the same relative angle with the reference systems as the bearing of the distant transmitter makes with the loops. In modifications, three exciting coils spaced at 120 degrees carry currents displaced in phase by 120 degrees, or four exciting coils with their axes at right angles carry currents displaced in phase by 90 degrees. Specification 490,940, [Group XL], is referred to.