Patent GB-813702-A (GB)
Title: A method for determining the position of the core of a body consisting of a core and a mantle, shell or sheath
IPC: G01R31/02
Filed: 1956-03-23
Abstract: 813,702. Electric tests. FISCHER, E. March 23, 1956 [March 26, 1955], No. 9080/56. Class 37. The eccentricity of a cable core or the bore of a tube is determined by measuring the thickness of the insulation or tube wall at various points around the circumference of the tube. As shown, the cable 62 under test passes through a housing 65 which is driven by motor 66 and gearing 68, 69 to rotate around the cable. Rotating with the housing are guides 90 and 87 (Figs. 2 and 3). Guide 90 consists of a pair of conical wheels riding on the cable and guide 87 of a pair of jaws which are adjustable by micrometer screws 88. Behind jaws 87 is a coil 2 forming part of the oscillatory circuit of a transistor oscillator (Fig. 1), the frequency of oscillation of which varies in accordance with the distance of the core from the coil as the head rotates around the cable. Also driven by motor 66 is a cam operating pairs of switches at periods separated by 90 degrees of the rotation of the housing about the cable. A spring 82 tends to slide jaws 87 with oscillatory coil 2 and the housing 79 containing the transistor into contact with a stop 84, and an adjustable screw 83 determines the setting position of these jaws. A further pair of transformers 6, 11 the purpose of which is described below have their secondaries and primaries respectively on the rotating part of the housing which is earthed by slip ring 76 and contact 77. Circuits (Fig. 1).-The transistor oscillator is  energized by the output of a 100-kilocycle oscillator 5 which is fed through transformers 6, rectifiers 7 and a filter circuit. The transistor oscillator has a mean frequency of 500 kilocycles variable by the distance of the core from the coil. The oscillator output is fed through transformer 11 to amplifier 13 and amplifier and limiter 15 which feeds a constant-amplitude voltage to a frequency discriminator consisting of circuit 13 so tuned that its mean frequency is on the straight portion of the resonance curve. A secondary winding coupled to the inductance in the oscillatory circuit feeds a demodulating diode 19 the output of which is fed to amplifiers 22, 27 and 28 which amplify very low frequencies and are provided with hum filters. The output of amplifier 28 is fed to a potentiometer 32 and from there through a filter resistor 33 to the control grids of tubes 34, 35 simultaneously. Tubes 34, 35 are made conducting by a camoperated switch 48 (reference 70 in Fig. 2) which completes their earth circuits with a phase difference of 90 degrees corresponding to a 90 degrees displacement of coil 3 around the cable. During closure of one of switches 46, 47 one of condensers 41 is charged to the anode potential of the appropriate tube 34 or 35 and this voltage is maintained during the remainder of the cycle. One of condensers 41 controls the potential of one of the vertical deflection plates and the other condenser one of the horizontal deflection plates of a cathode-ray tube 43. An oscillator 49 feeds two sinusoidal wave forms separated in phase by 90 degrees to the other plates so as to provide a circular trace. This trace is displaced angularly depending on the charges on condensers 41 to indicate the eccentricity of the core. Cam 48 may be angularly adjusted to take account of the twist of the cable leaving a machine so that the cathode-ray tube indicates directly where the eccentricity of the core is being produced. If the size of the core is required the mean of the discriminator output may be used to control the amplitude of the output of oscillator 75. Modifications.-Fig. 4 shows an arrangement for measuring the bore of a tube 102 being extruded from a housing 101. In this case a magnetic block 105 mounted by roller bearing 108 having telescopic support 104 is drawn by magnet 107 into contact with the inner wall of the tube and forms part of the inductive circuit of oscillator 109 which rotates about the tube with magnet 107, the block meanwhile rolling around the inside of the tube. The Specification also mentions the possibility of using a number of separate heads positioned circumferentially around an object under test and connected sequentially into the oscillatory circuit by a switch. A further possibility is a head which oscillates about the test object but does not complete the full circle. An electrostatic field may also be used.