GB992498A - Improvements in surveying instruments - Google Patents

Abstract

992,498. Surveying Instruments. S. H. F. SARL. May 10, 1963 [May 10, 1962], No. 18083/62. Heading G1F. A surveying instrument comprises a mirror unit A, Figs. 1, 5, having a plane mirror 8 thereon, a separate target unit B, Figs. 2, 9 having a target 11 thereon which is the same shape as the mirror but has linear dimensions twice those of the mirror, the mirror being mounted so that it can be set truly vertically and/or horizontally after the mirror unit has been set with its mirror viewing face substantially vertically or horizontally, respectively. The mirror unit is mounted on a slide 1a which is adjustable with respect to a straight edge 1. The straight edge 1 has a spirit level 9 and the slide 1a may be clamped in any desired adjusted position by means of a screw 5. The mirror 8 is mounted behind an aperture 31 in the mirror unit and is held in a frame 13 pivotally mounted on a fixed rod 14. The mirror 8 may be pivoted about the rod 14 by rotation of a screw 17 against the action of a spring 18. A spirit level 19 is mounted on a bar 21 integral with the frame 13 to enable the mirror to be adjusted to a truly vertical position. The area surrounding the aperture 31 consists of two similar areas coloured black and white respectively. The target unit B is also mounted on a slide 2a, which is adjustable relative to a straight edge 2. The target 11 consists of two equal area black and white coloured portions. An eyehole 12 passes through the target unit, a spirit level 26 being mounted in the unit so that its bubble can only be seen when the level is horizontal. The target 11 is rotatably mounted on a support 27. In use Fig. 12, the mirror unit is set with the level 9 so that the straight edge 1 is substantially vertical. The mirror 8 is adjusted to the vertical and the mirror is viewed through the eyehole 12 the height of the eyehole and target 11 being adjusted until the image of the target covers the mirror 8. The height difference between the two points X, Y on which the straight edges 1, 2 are resting can then be calculated from the relative positions of the slides 1a, 2a with regard to the straight edges. The instrument may also be used to set up one point vertically above another the mirror unit being provided with a circular spirit level to enable the mirror to be set horizontal, and further may be used to set up points offset from a base line. As alternative features the mirror 8 may be mounted in a ball and socket joint, or may be mounted as a pendulum with suitable damping so that adjustment would be unnecessary.