GB818345A - Improvements in or relating to the measurement of surface texture and apparatus therefor - Google Patents

Abstract

818,345. Electric tests. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Nov. 1, 1957 [Aug. 3, 1956], No. 23962/56. Class 37. A probe for measuring surface roughness comprises an electric condenser which, when close to the surface, forms an electric condenser with it, and which is mounted in an insulating housing having a rim which extends beyond the conductor the whole being mounted in a probe holder which contains means for urging the rim into engagement with the surface while leaving the probe free to tilt so that the rim can level itself on the surface. In the arrangement shown, the conductor 12 has a cylindrical centre and reduced ends and is clamped in insulating housing 13 by a nut clamping on insulating washer 18. The end 13a of the housing extends below the conductor which is thus spaced from the surface under examination. To maintain the probe in contact with the surface, while allowing it to tilt a spring 21 fastened to the probe holder 18 presses a ball 20 into engagement with a member attached to housing 13 and extending into electrode 12. In a further arrangement (Fig. 7, not shown), the central conductor is provided with two bores at right angles to its axis and to each other. One houses a rotatable pin having a central flat and the other a spring which presses a ball on to the flat. Fig. 8 shows a further arrangement in which the electrode 42 is mounted in an insulator 43, 44 on which bear a pair of springs 45. The capacity changes of the probe may be used to control the frequency output of an oscillator which, either heterodyned with a fixed frequency and the beat frequency measured or measured in a bridge circuit.