Improvements in electrical testing and measuring apparatus and in methods of effecting electrical tests and measurements

摘要

576,344. Correspondence control systems. MARCONI INSTRUMENTS, Ltd., BARTLEY, W. B., and BROCKELSBY, C. F. Jan. 17, 1944, No. 892. [Class 40 (i)] [Also in Group XXXVI] A conductor to be located varies the screening between two electrical systems. Fig. 1 shows an arrangement for determining the eccentricity of the conductor in an insulated cable. The cable, consisting of the conductor 1 and insulating sheath 2, is guided between metal plates 3, 4. Adjacent parts of conductors 11, 12 run parallel to the conductor 1. The conductor 11 carries an alternating current, a voltmeter being connected to the conductor 12. The conductor 1 and the plates 3, 4 form a screen between the conductors 11, 12, this screen being symmetrical if the conductor 1 is co-axial with the sheath 2. Any eccentricity of the conductor 1 causes unsymmetrical screening and a consequent indication on the voltmeter. In a modification, Fig. 2, a source 10 of alternating E.M.F. is arranged to produce potentials of equal amplitude and opposite phase relative to earth on metal plates 5, 6. A metal plate 7 is connected to earth through an instrument 8. Earthed plates 3, 4, in conjunction with the conductor 1, form an electrostatic screen between the plate 7 and the plates 5, 6, the symmetry of this screen being upset by any eccentricity of the conductor 1. A similar system at right angles to the one shown will show displacements in a direction at right angles to the plates 3, 4. These two indications may be combined on the screen of a cathode-ray oscillograph to indicate the position of the conductor 1. The displacement currents may be separately employed to restore the conductor 1 to co-axiality in succeeding portions of the cable during manufacture. The system may also be used to detect the movement of a metal object moved by a device to indicate liquid level, rate of flow, specific gravity, or pressure, and also to detect the movement of the pointer of an electrical measuring instrument indicating temperature, pH value, conductivity, voltage, current, or frequency. The current due to the unbalance may operate auxiliary gear for the control of any process or quantity, or to restore its earlier condition.