GB912042A - Improvements in or relating to apparatus for measuring small distances - Google Patents

Abstract

912,042. Interference microscopes. WAYNE KERR LABORATORIES Ltd., and CALVERT, R. April 14, 1961 [Jan. 14, 1960], No. 1427/60. Class 97 (1). [Also in Groups XIX, XXXVI and XXXVIII] Apparatus for measuring small distances between surfaces, e.g. the depth of a hollow or depression, comprises an interference microscope and a polychromatic light source, the microscope being provided with means for measuring movement of the objective towards or away from the surface. Microscope 13 is connected through flexible strips 19 to member 12 which is clamped to pillar 11 and carries an adjusting screw 20. The screw acts on one end of lever 21 which is pivoted at 22 and acts at its other end on the microscope at 25. A lug 26 on the microscope co-operates with a probe unit 27 to form a variable capacitor, the capacitance of which is a measure of the vertical position of the microscope, and which is connected in a measuring circuit. An embodiment using a differential transformer as a transducer is also described (see Group XXXVIII). In use the microscope is first adjusted so that the central dark interference band is at the bottom of the hollow and is then readjusted so that it is at the top of the hollow. The difference in reading of the indicator gives a coarse measurement which may be corrected by counting the number of interference fringes between the selected fringe and the top or bottom of the hollow. Specifications 762,396 and 912,041 are referred to.