Patent GB-343917-A (GB)
Title: Improvements relating to seismographs, and applicable to other measuring instruments
IPC: G01V1/18
Filed: 1929-11-21
Abstract: 343,917. Weighing-apparatus. ANGLOPERSIAN OIL CO., Ltd., Britannic House, Finsbury Circus, London, and JONES, J. H., 22, Milward Crescent, Hastings. Nov. 21, 1929, No. 35711. Addition to 323,552, [Class 143, Weighing-apparatus]. [Class 143.] Indicating and registering mechanism.-In the instrument of the parent Specification, the iron armature or magnetic element is suspended in a magnetic field produced by a plurality of magnets so disposed that the lines of force in which the armature is set are not only strongly curved but also concentrated to a greater intensity than that secured by a single magnet. In the seismograph shown in Figs. 1, 2 a base a mounted on three levelling screws supports a pedestal b which in turn supports a baseplate c provided with an opening c<1> for the member carrying the magnetic element. Parallel slides c<3> on the baseplate adjustable by screws c<7> against springs c<8> carry parallel cross-slides adjustable by screws c<9> against springs c<10>. Magnets d, e are clamped to the slides. The pole pieces d<1>, e<1> are curved and adjustably mounted on the ends of the magnets. The pole shoes e<1> receive coils e<2> connected to terminal e<3> which in turn are connected to terminal e<4> in the base of the instrument. The coils are curved so that a current may be passed in such manner that a modification of the magnetic field produced by the magnet e is secured both as regards intensity and direction so that a distorted field may be effected for zero adjustment of the magnetic element. The magnet d may be similarly fitted with control coils. The magnetic element f comprises a thin iron strip carrying a mirror f<1> and suspended between the gaps of the shoes d<1>, e<1> and nearer to the shoes e<1> than to the shoes d<1>. The pole gap of the shoes e<1> is filled by a mass of copper provided with flanges of mica &c. to position and support the mass. The base-fitting a supports the weight of the seismograph by an upstanding piston a<1> which forms the foot of the pedestal h. The weight has a cylindrical case supported by pairs of spring strips g<1>, g<2>, and is controlled by a spring g<3> attached at one end to a lug g<4> on the weight and at the other end to an adjusting screw g<5>. The weight g may be fixed for transport from below by bevelled chucks a<9> adjusted by a right- and lefthanded screw and from above by a co-operating member b<1> hinged to the pedestal and pressed down by a screw b<2> against the influence by a spring b<3>. The weight supports a light conical helm h of thin copper to which is attached a phosphor bronze wire i which passes over the bridge fittings h3, h4, h5 and under a part h<6> to a spring j adjustably secured to a bracket on the weight. The element f carrying the mirror is mounted on the wire i between bridges h<4>, h5. The instrument is enclosed in a casing k with hinged hood k<1>, which is formed with a window k<3> to permit passage of a beam of light from a source and its reflection to a sensitized surface. In operation, when the element f is moved as the result of vibrations of the helm, it will set itself tangential to the lines of force and in so doing will partly rotate causing the vibrations to be recorded on a moving sensitive surface. The vibration may be imparted to the magnetic system rather than to the element, and may be used in oscillographs.