Patent GB-835436-A (GB)
Title: Improvements in or relating to apparatus for measuring in digital form constantly varying electric currents or voltages
IPC: H03M1/00
Filed: 1956-10-01
Abstract: 835,436. Electric selective signalling systems. SIEMENS & HALSKE A.G. Oct. 1, 1956 [Sept. 29, 1955], No. 29896/56. Class 40 (1). [Also in Groups XXXVI and XXXIX] In apparatus for measuring digitally a variable current or voltage e.g. in binary numbers, plural annular magnetic cores with rectangular hysteresis loops are all interlinked with a first conductor carrying a measurement current and a second conductor carrying a pulsating current in such manner that the measurement and impulse currents induct oppositely directed fields in each core; the couplings of individual loops with their respective cores being made variable in such manner that each core changes from one to another magnetization state for a predetermined distinct value of measurement current, whereby such changes of state in combination afford indication of the values of the current or voltage to be measured. In Fig. 1, magnetic cores 11 to 15 having rectangular hysteresis loops are energized by conductor 2 carrying the current to be measured and having graduated numbers of turns linked with the cores so that each is premagnetized by a given current to a different degree as shown by the chain lines 3 in the respective hysteresis diagrams. A conductor 4 linking the cores carries a pulsating direct current inducing therein a superimposed field exceeding twice the core coercivity. The field amplitudes are such that cores 11 and 12 maintain their original state of magnetization (a) while the magnetization of core 13 changes over with each current impulse in conductor 4 while returning to its initial condition due to the measurement current at the end of each impulse, after traversing the hysteresis loop shown. An impulse of current induced thereby into conductor 6 linking the core is rectified for indication. Cores 14, 15 are also impulse magnetized to states denoted by points b of their hysteresis curves, but the current is now unable to reverse magnetize the cores to the respective initial states denoted by points a, since the pregmagnetization derived from the measurement current is so small that point b is disposed on the upper horizontal arm of the loop in response to the impulse current magnetization. On reversal of magnetization each core produces an impulse signal in winding 6 for a predetermined specific value of measurement current, which signal is applicable to operate an indicating member such as a relay or glow lamp, and since the degree of premagnetization by measurement current in each core is graduated in accordance with the number of turns of conductor 2, the number of cores suffering reversal of magnetization and thus producing indications are thus determined by the magnitude of the measurement current, and may operate a binary indicator display. In Fig. 2, four magnetic cores 21, 22, 23, 24 are linked by a closed current loop 7 energizing all remaining cores in response to a unidirectional impulse induced therein by a particular core, and conductors 2, 4 carrying the measurement and pulsating currents; the fluxes in the successive cores due to a given measurement current being graduated in the ratios 8:4:2: 1 so that the flux in core 21 is repeatedly reversed in response to pulsed energization over conductor 4 for a measurement current of at least 18 units, that in the core 22 for a current of at least 4 units, and similarly in cores 23, :24 for currents of at least 2 and 1 unit. Currents are accordingly induced in the windings of the other cores such as to induce fluxes corresponding to current values of 8, 4, 2 or 1 units according to the core or cores whose magnetic flux is repetitively reversed. When a measurement current of e.g. 13 units flows in conductor 2 the magnetic flux of core 21 repeatedly reverses and fluxes corresponding to 8 units are induced in cores 22, 23, 24. The flux in core 22 repeatedly reverses in response to the measurement current to derive a current in conductor 7 which superimposes upon the flux in core 21 a flux derived in core 22 and corresponding to 4 units. The measurement current also excites cores 23, 24, but core 23 is not reversedly magnetized since at least 2 units of current are necessary to do so and the reverse current produced by cores 21, 22 over conductor 7 corresponds to 12 units, while the measurement current is 13 units. Core 24, however, being such that 1 unit of current is necessary to reversedly magnetize it, repeatedly reverses its flux. Cores 21, 22, 24 thus respond so that indicators respectively associated therewith display code 1101 if 1 denotes reverse magnetization and 0 denotes constant magnetization; corresponding in binary notation to value 13. At a current value 14 units, core 23 is reversedly magnetized and the current in conductor 7 develops a field in core 24 corresponding to 2 units, so that the measurement and reverse fluxes cancel and the core magnetization is unaltered. The binary code 1110 is then indicated to represent 14 units. The measurement current is applied in successive pulses over switch S and during the intervals the cores are reset by impulses over conductor 4. In a modification (Fig. 3, not shown) lamp or relay indicators are operatively coupled to their respective first cores through corresponding second cores whose magnetization is reversed by the occurrence of an impulse from a first core to trigger the appropriate indicator and restored by periodic impulses of current in a common. conductor.