GB630448A - Improvements in or relating to indicating instruments - Google Patents

Abstract

630,448. Indicating. LIQUIDOMETER CORPORATION. Feb. 24, 1947, No. 5294. Convention date, June 28, 1946. [Class 106 (iv)] [Also in Groups XXXVI and XXXVIII] An indicating instrument having provision for moving the indicating element to a predetermined off position when the instrument is not operating comprises means movable between an inoperative position where it is electrically and mechanically separate and distinct from the means for effecting the normal indicating movement of the indicating element, and an operative position where it will effect movement of the indicating element to the off position, means operated in response to the energization of the element moving means for holding the movable means in its inoperative position during all the time the indicating element is positioned by the element moving means, and means effective to move the movable means to its operative position on de-energization of the element moving means. A ratiometer type instrument for indicating liquid level in a tank 12 is shown. The transmitter comprises a resistance 13 divided into three sections by taps 14, 15, and engaged by a wiper 16 which is moved by a float 18. The indicating instrument 10 comprises three fixed coils 21, 22, 23, spaced about a permanent magnet rotor 24. This may include two similar permanent magnets 25, 26, Fig. 2, spaced apart on a common rotor shaft 27, the disc-like coils 21, 22, 23 being arranged between the magnets 25, 26. The shaft 27 carries a pointer 28, which moves over a scale 29. The inner ends of the coils 21, 22, 23 are connected together and their outer ends are connected through resistances 30, 31, 32 and a switch 54 to one pole of a battery 56, the other pole of which is connected to the wiper 16. The outer ends of the coils 21, 22, 23 are also connected to taps 14, 15, 35, 36 on the resistance 13. An auxiliary permanent magnet 58 is mounted on an arm 60 pivoted at 61, so that the magnet 58 can swing through an intermediate position 62, to an operative position 63. The resistors 30, 31, 32 are wound on a cast iron core 69 having a pivoted armature 71. When the instrument is energized by closing the switch 54 the armature 71 is attracted to the core and pulls the arm 60 to its inoperative position against the action of a spring 64, so that the magnet 58 is out of the field of the rotor magnet 26. On deenergization of the instrument the armature 71 is released and allows the magnet 58 to move to the position 63 under the action of the spring 64, in which position it acts on the rotor magnet 26 so that the pointer 28 is moved off-scale to the position 59. Should the pointer 28 be in the position shown, diametrically opposite to the position 59, the magnet 58 in the position 63 would exert equal and opposite torques on the rotor. This dead point position, however, is eliminated by the action on the rotor of the magnet 58 in the intermediate position 62, which starts rotation of the rotor.