GB1056891A - Improvements in or relating to methods of and apparatus for continuously and directly measuring capacity unbalances of four-wire telephone circuits - Google Patents

Abstract

1, 056, 891. Measuring capacitance. SOC. ANON GEOFFROY-DELORE. Jan. 13, 1964 [Jan.11, 1963], No. 1456/64. Heading G1U. To measure capacity unbalance in a four wire telephone circuit one pair P 1 is energized by alternating current and the voltage induced in the other pair P 2 if there is any unbalance, is observed. Measurements may be taken continuously during manufacture of a telephone cable by apparatus connected at one end only and the capacities balanced in any known way. In Fig. 1, the pair P 1 is energized from an A. C. source 5 through a screened transformer T and the voltage induced in the pair P 2 is rectified by a contact converter I and fed to a ballistic galvanometer G which is calibrated to indicate the unbalanced capacity. Alternatively the rectifier I may be omitted and a centre zero galvanometer used, Fig. 2 (not shown). The transformer T may be fed from a bridge rectifier. With the arrangement described above the galvanometer reading is a function of the cable length. In another embodiment (Fig. 3) the sensitivity of the galvanometer is varied by controlling its exciting current in winding 6a in dependence on the charging current of the pair P 1 , which depends on their length. An ammeter 3 in series with the secondary of the transformer T has a rotating cam-shaped disc which controls the light falling on a light-sensitive resistance in the galvanometer excitation circuit. The galvanometer may be replaced by circuits using thermionic valves or transistors. For example the signals induced in the second pair may be fed to grids of two valves, each valve having a bias voltage on another grid controlled by the light-sensitive resistance referred to above, and the valves controlling a meter indicating unbalance in one direction.