GB762395A - Improvements in or relating to distance measurement - Google Patents

Abstract

762,395. Electric measuring systems. WAYNE KERR LABORATORIES, Ltd., and CALVERT, R. April 4, 1955 [April 2, 1954], No. 9731/54. Class 40 (1). [Also in Group XXXVI] Apparatus for measuring the distance between a probe and an electrically conductive body comprises a self-balancing alternating- current electric bridge for determining the capacity between the probe and the body in which the bridge is balanced by adjusting the voltage applied to the capacity and in which means are provided for indicating the said voltage. The ratio arms of the bridge are formed by the two secondary windings 13, 14 of a transformer 11, the former winding feeding a variable amplifier 18, one output terminal of which is connected to one end of winding 14. The primary winding 12 is fed from an alternating current source. The capacitance 10 formed between the probe and the body is connected in series with a standard capacitance 15, which may be adjustable, across the other output terminal of amplifier 18 and the other end of winding 14. The primary winding 16 of a transformer 17 is connected between the junction between amplifier 18 and winding 14, and the junction between the two capacitances. The output of the secondary winding 19 is fed to a rectifier 20 providing a direct-current signal which adjusts the gain of amplifier 18 in the sense to balance the bridge if a resultant voltage across winding 16 indicates out-of-balance. The body may be a milling cutter to be tested for the height of its teeth, or other cyclically moving body. In this case the output of amplifier 18 is fed to one pair of deflector plates of a cathode-ray tube 22, the other pair being connected to a time base 25 synchronized with the cyclically moving body.