Magnetic field-sensing apparatus

Abstract

Abstract 1416940 Magnetic position indicators SIEMENS A G 21 Aug 1973 [21 Aug 1972] 39666/73 Addition to 1329627 Heading G1N Apparatus for use in such devices as position indicators, limit value signallers or null indicators of the type which includes two magnetic field sensors and a magnetic flux generator movable relative thereto as shown in Specification 1329627 has the magneto-resistors connected in a differential circuit. Position indicator, Fig. 1 Two magnetic field sensing devices 2, 4 including permanent magnets 10, 11 flux return paths 13, 15, 17 and 12, 14, 16 and magneto resistive members 18, 19 are separated by a gap 5 filled with diamagnetic material such as air. A magnetic flux generator in the form of a permanent bar magnet 6 is mounted on the apparatus whose position is to be indicated e.g. a rotatably movable member so that it moves past the devices 2, 4 in the direction of arrow 8. The magneto-resistive members are connected in adjacent arms of a D.C. energized resistance bridge. As the bar magnet 6 moves either to the left or right of the position shown the magnetic flux in one of the magnetoresistive members varies whilst the net flux in the other member remains more or less constant. Thus the output voltage across a bridge diagonal varies positively and negatively linearly with the displacement of the magnet 6 over a limited range, Fig. 3 (not shown) and is insensitive to variation in the distance "b" between the magnet and field sensing devices. Limit value signaller, Fig. 6 The arrangement of Fig. 1 is modified by the magneto-resistive members being remote from each other. When magnet 6 is displaced from the central position there is little variation in the resultant magnetic flux passing through the magneto-resistive members and the bridge output remains zero. Beyond a certain range of movement (dead zone) a positive output maximum is produced (movement to the left) or a negative output minimum (movement to the right). Another arrangement having a "dead zone" comprises two sensing devices as shown in Fig. 1 but the magnet 6 is in the form of a U-shaped magnet whose respective pole limbs extend towards the devices respectively.

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