GB881071A - Improvements in or relating to measuring and testing apparatus - Google Patents

Abstract

881,071. Capacitors; determining physical dimensions. HAYNES & HAYNES Ltd. Jan. 20, 1960 [Jan. 30, 1959], No. 3364/59. Addition to 880,184. Class 37. Apparatus for measuring variation in wall thickness or eccentricity of a polythene tube P comprising a pair of capacitive electrodes 26, 28 between which the tested tube is passed and a reference capacitor as described in the parent Specification, the latter comprises a pair of electrodes 30, 32, the capacitance of which is manually adjustable by movement of an earthed conductive member 50 between them. As shown, the measuring head comprises a split cylindrical screening case 10 hinged at 14 and having cut-out portions 20, 22 to accommodate the polythene tube P. The tube P is supported by V-blocks 66, 68 of nylon loaded with molybdenum disulphide. The measuring head 10 may be self-supporting on a moving tested tube by PTFE blocks 70 mounted on levers 72, pivoted at 74 and biased towards the tube by means of springs such as 76. The measurement is dependent on variations in capacitance of electrodes 26, 28 due to variation in wall thickness, compared with that of a reference capacitor comprising electrodes 30, 32. The capacitive electrodes are formed by depositing silver on an insulating plate 24 of material known under the Registered Trade Mark " Perspex." The reference capacitor is adjusted by movement of a tapered earthed conductive member 50 between the electrodes 30, 32 under control of a knob 64 at the end of a screw 58. The measuring head 10 is rotated around the tested tube P for eccentricity measurements.