GB1056713A - Moving scale instrument - Google Patents

Abstract

1, 056,713. Indicating-apparatus. SPERRY GYROSCOPE CO. Ltd. Sept. 22, 1965 [Sept. 22, 1964], No. 38568/64. Heading G1J. The moving scale of a compass repeater comprises an endless flexible tape 17 of plastics material guided by two sets of five aluminium alloy pulleys 12 to 16 and 12<SP>1</SP> to 16<SP>1</SP> to form two sets of runs respectively adjacent opposite sides of a base 11 and linked by two runs adjacent one end whereby the area between the two sets is free to house an A. C. motor 22, amplifier 24 and fine and coarse synchros 21, 20. A master compass applies signals to the stators of the synchros whose rotors apply error signals through the amplifier 24 to the motor 22. The motor 22 rotates the rotor of the coarse synchro and also gears which drive the rotor of the fine synchro and the pulley 16 which is toothed to drive the tape 17. The arrangement is thus a null-seeking servo system wherein the tape and rotors are driven until the error signal becomes zero. A switch is provided to disconnect the master compass and apply a voltage to set the repeater to read zero, whereupon the pulley 16 can be locked, the main fuse removed and the tape renewed. A limb 26 of an "L" section sheet of transparent plastics material is inserted between the tape runs 12, 16 and 15, 13, its back surface is sandblasted so that when edge lit from light sources, transparent graduation marks on the front run of tape can be read against a stationary indicator. In another embodiment the indicator may be a transparent plastics rod with one side whitened. A sheet of translucent plastics between runs incorporates three miniature lamps in its lower half which illuminate the graduations through red filters while the centre lamp only directs some clear light on to the indicator so that it appears white.