GB920168A - Improvements in or relating to thickness measuring instruments - Google Patents

Abstract

920,168. Magnetic testing apparatus. SIGMA INSTRUMENT CO. Ltd. May 26, 1961 [May 9, 1960], No. 16234/60. Class 37. A thickness measuring instrument includes a detector, which contacts one side of the test material and has an armature for magnetic cooperation with a magnetic pole of a mechanically separate member for encountering the opposite side of the material, means for applying a controlling force to the armature to counterbalance the magnetic force applied to the armature by the pole, and indicating means responsive to the latter force. Magnet 3, Fig. 1, and point 7 abut against the opposite surfaces of sheet 1 of non-magnetic material, the thickness of which is measured by the vertical movement, with respect to the frame 4, of the magnet 9 suspended by spring 10. A modification, Fig. 2 (not shown), employs a cylindrical magnet held against the underside of the material by the magnetic attraction of a co-operating magnet mounted at one end of a pivoted lever on the other side of the material; the cylindrical magnet rolls over the surface of the material when the latter is moved relative to the apparatus. In a further embodiment, Fig. 3 (not shown), a first magnet mounted on a micrometer spindle is held stationary against the lower surface of the sheet 1, and a frame bearing a pivoted magnet system and scale is located above the first magnet by seeking the position of minimum scale reading; in this position the instrument can be calibrated by adjusting the micrometer to the appropriate reading with a known thickness of material, the micrometer reading corresponding to adjustment to return to the same scale reading subsequent to the introduction of the test material giving the thickness of the latter. Reference is made to the use of an air jet for applying the controlling force to the armature. The Provisional Specification refers to mechanical, electrical, or optical amplification of the armature movement, to the use of the detector unit for the location of iron pipes in brick walls, and to the use of the position of unstable equilibrium of opposed magnetic and spring forces for the indication of a minimum thickness. The Provisional Specification further refers to an instrument in which the detector unit and the member for encountering the opposite side of the test material are mechanically connected by a magnetic leafspring.