Patent GB-711206-A (GB)
Title: Improvements in or relating to gravimeters
IPC: G01V7/08
Filed: 1949-05-11
Abstract: 711,206. Measuring force of gravity. ANGLO-IRANIAN OIL CO., Ltd., and TOMASCHEK, R. K. A. Aug. 11, 1950 [May 11, 1949], No. 12544/49. Class 97(3) [Also in Groups XXXII, XXXVIII and XL(b)] The gravimeter comprises a coiled spring 3, Fig. 10, having a cross-secton of substantial width to thickness ratio and having not less than 1.25 turns in the unextended state, means attached to one end of the spring for movement under the force of gravity and a mounting 2 for supporting the other end of the spring so that its longitudinal axis in the unextended state is inclined at an angle not greater than 40 degrees to the vertical, the angle being such that under the influence of the force the spring is extended into a state of extreme sensitivity. The spring is in such a state when the mounting angle is such that the graph of angle of twist against load is a simple inflection one having the maximum sensitivity for twist and the load is that at which the latter occurs. The rigid framework 1 supports the adjustable mounting 2 which rigidly clamps the inner end of the coiled flat section spring 3 having about three turns when undistorted. The outer end of the spring is attached to a small mirror 4 to which is attached a rod 5 the latter being connected at its lower end to a delicate helical spring 6 whose tension is controlled by a rack 7 and pinion 9 operated by a horizontal shaft 10. A delicate helical spring 8 extends between the clamp 2 and mirror 4. A double-bladed vane 11 on rod 5 moves between quadrants 12 disposed as in a quadrant electrometer, pairs of quadrants being connected to an electronic circuit for measurement of the capacity between them and the vane and hence the angular disposition of the latter. Two adjacent quadrants are attached to a movable support 13 for adjustment in a vertical direction. A horizontal damping disc 14 on rod 5 has its periphery lying between the pairs of poles of two diametrically positioned horse-shoe magnets 15. Clamps may be provided for locking the rod 5 against horizontal, and disc 14 against vertical movements when the apparatus is not in use. In modifications the angular disposition of the spring 3 is measured by employing a photoelectric method and utilizing a beam of light reflected from the mirror 4, or using a radioactive method in which the ionization in two or more chambers is changed. Alternatively the linear distortion of the spring may be measured such as by a travelling microscope. In one form of spring mounting, Fig. 12, the spring 20 is clamped to a support 21 carried by bevel gear 22 mounted on a cranked arm 23 supported by the casing 19. A second bevel gear 24 engaging gear 22 is carried on a shaft 25 within one arm of 23, adjusting wheels 26, 27, enabling the spring to be tilted in mutually perpendicular directions. In a modification of the mounting, Fig. 14, the spring 30 is clamped to a support 31 attached to ballsocket 32 carrying four vanes such as 33, 36. A ball 37 on rod 38 is enclosed by the socket 32. Two adjacent vanes are acted on by spring loaded rods such as 40, the others being positioned by screws usch as 42 threaded through the casing 39. In a further embodiment, Fig. 16, a rigid support 50 carries an adjustable support 51 for clamping the upper end of the sensitive spring 52. The lower end of the spring carries a mirror 53 and is connected by torsion wire 54 to the horizontal arm 56 of an angularly movable framework 57 which is supported by torsion wires 58, 59, attached to rigid pillars 60, 61, and torsion wire 62 attached to pillar 63. A sphere 64 is carried by arm 56 and a helical spring 65 considerably weaker than spring 52 stabilizes and restricts the movement of the latter spring. The sensitive spring may be critically loaded by a rider weight carried by arm 56 or an external force applied by electrical, magnetic or other means to the arm. Specification 711,205 is referred to.