GB1007932A - - Google Patents

Abstract

1,007,932. Selective signalling systems. VENNER Ltd. April 24, 1962 [April 28, 1961], No. 15547/61. Heading G4H. The output of a counter is displayed by a moving-coil meter having a scale 18 and means to lock the coil in any of its display positions while a counting operation is taking place. The moving coil 4 carries a disc 20 having teeth 22 which pass through the air gap of a C-shaped permanent magnet 24, the magnetic attraction between a tooth 22 and magnet 24 ensuring that a digit on scale 18 is correctly displayed. Several alternative methods of ensuring correct positioning are described, for example disc 20 may have a single radially extending arm which co-operates with a toothed magnet, Fig. 4 (not shown), or disc 20 may act as the magnet, or magnet 24 may be an electromagnet. Several methods of locking coil 4 are also described. When magnet 24 is a permanent magnet, it may be provided with a winding which is energized during a counting operation to increase the attraction between a tooth 22 and magnet 24 to such an extent that the maximum torque which coil 4 can exert is not sufficient to overcome the attraction. A more economic method is to make the. attraction between magnet 24 and teeth 22 large enough to prevent movement of coil 4, and to energize a winding on magnet 24 to reduce the attraction for a short period after a counting operation. Fig. 7 shows a pawl-and-ratchet type of arrangement in which a disc 25 carried by coil 4 is simultaneously positioned to display the correct digit and locked in that position as pawl 27 engages an indentation 26. Another mechanical locking arrangement which may be used with any of the magnetic positioning arrangements described comprises a solenoid-releasable friction pad engaging disc 20. The digits on scale 18 may be optically projected.