GB880199A - Improvements in or relating to precision balances - Google Patents

Abstract

880,199. Weighing-apparatus. STEFFES,K. June 18, 1959 [June 28, 1958], No. 20903/59. Class 40 (1). [Also in Group XL (b)] A precision balance contains an auxiliary beam which is caused to follow the movement of the main beam by a closed-loop servo system, the deflection of the main beam being sensed by a magnetic coupling or by photoelectric means. In the Figure, the balance beam 1 carries the core 6 of a differential transformer whose primary 5a is energized from a current source 9. When the beam is deflected an output is obtained from the secondary 5b as a voltage whose phase sense depends on the direction of deflection of the beam. This voltage is amplified at 14, passed through a conventional " proportional-differential " anti-hunting network 15 and applied to a motor 11 to cause it to run in one direction or another according to the displacement of the beam. The motor rotates a shaft 19 through gearing 17 and also drives a digital indicator 22. The shaft drives a nut 20 which bears against an auxiliary beam 3 and thus moves the transformer secondary 5b to a new null position. Movement of this auxiliary beam can be used in known matter to provide a remote indication of the position of the balance beam. The digital indicator 22 is calibrated in tens and, for establishing the initial and terminal points of the deflection of the balance, contains a unit of ten or part thereof more than is required for the deflection. The differential transformer can be replaced by a light source on the beam co-operating with a pair of photo-cells. The apparatus can be used for tolerance weighings.