GB985426A - Improvements relating to apparatus for exploring the contour of a conductive surface - Google Patents

Abstract

985,426. Determining physical dimensions. FAIREY ENGINEERING Ltd. Oct. 26, 1961 [Oct. 27, 1960], No. 36957/60. Heading G1N. [Also in Division G4] In an apparatus for exploring the contour of the conducting surface of a workpiece a single electrode probe is moved along a path in which it is spaced from the surface by a small gap and means responsive to capacitance is provided to indicate the width of the gap. The probe may be driven along a predetermined path by a programme arrangement and the gap variations be recorded, or the probe may be controlled by the gap to maintain a constant gap width and the path of the probe be recorded. Various electrode arrangements for particular shapes of workpiece are described with reference to Figs. 1-4 (not shown), and a universal spherical probe 13 is shown in an arrangement, Fig. 5, wherein the workpiece probe gap is maintained constant by a servomotor 32 in response to the beat between a reference oscillator 30 and an oscillator 31 which includes the gap capacity in its tuned circuit. In an alternative arrangement the gap is connected in series with a resistor 42, Fig. 6, and the potential developed across the capacitor from a source 41 is demodulated in 45 and amplified in a linearising amplifier 46 which may comprise an amplifier 61 (Fig. 10) having the junctions point of series feedback resistors 63, 64, connected to a plurality of circuits each including a semiconductor-diode 66 in series with resistor 65 connected to an adjustable negative D.C. source by a wiper 67. The amplifier without the diode circuit is of the vertical earth type, and the addition of the diode circuit changes the amount of feedback at a desired input level to give a desired linearisation. Zener diodes 73 are additionally inserted in the paths to remove the sudden changes.