GB980531A - Levelling instrument - Google Patents

Abstract

980, 531. Levels, inclinometers. M. J. HALL. Nov. 20, 1963 [Nov. 21, 1962], No. 45902/63. Heading G1F. A levelling instrument comprises a sighting tube 12, a rotatably mounted sight carrier 13, able to turn freely about an axis transversely to the tube, and two spaced sights 18 on the carrier 13 obtruding into the tube 12, the carrier being weighted so that it adopts a levelling position at which the sights 18 coincide with a horizontal line of sight through the tube.when the axis of rotation of the carrier 13 and the longitudinal axis of the tube 12 are both horizontal. The tube 12 is contained in a metal stock 11 having a plane base parallel to the axis of the sighting tube. Lenses 19, e.g. of plastics material are mounted at each end of the tube 12 and are provided with hair lines to define the horizontal line of sight through the tube. The carrier 13 is a metal casting having a central T-section hub containing a bearing and supporting a disc with peripheral flange portions. The sights 18 are mounted on the disc and because there is a greater weight of material provided below the bearing of the carrier 13, the carrier comes to rest with the top faces of the sights 18 which may be painted black in a horizontal line and in line with the hair lines on the lenses 19 if the tube 12 is also horizontal. The instrument may also be used as an inclinameter by the use of protractor scales provided on the side faces of the carrier 13 and veiwed through arcuate windows carrying datum lines in the stock 11, and by the use of drum-type protractor scales on the flange portions of the carrier disc which may be viewed through peep holes 41, 42.