Patent GB-716782-A (GB)
Title: Improvements in or relating to electrical signalling systems
IPC: H03K17/74
Filed: 1950-01-13
Abstract: 716,782. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Jan. 13, 1950 [June 2, 1949; June 21, 1949], No. 920/50. Class 40 (4) [Also in Group XL (b)] An electrical signalling system includes a distributer which comprises a static electrical switching element connected to each individual signal channel so as to form a branch circuit therefrom, each such element being controlled by pulse source so as to be conducting as a shunt to the channel during the "no-pulse" period but non-conducting during the "pulse" period, the pulse sources of the elements pulsing in turn cyclically so that a signal applied to one end of an individual signal channel is transmitted to the other end only in the time position characteristic of that channel, i.e. when its pulse source is "pulsing". A "static electrical switching element" is defined in the Specification as a device having a permanently positioned electrical path the effective impedance of which may be either of two different values, change from one to the other being effected by an appropriate change in a controlling electric or magnetic field from one stable condition to another, and includes, e.g. thermistor trigger circuits, discharge tubes, transistors, and metal rectifier circuits. As described, the invention is applied to the scanning of the outlets of telephone selectors. Scanning device for one group of lines: Fig. 1.-The terminals E1, E2, E3 are connected to the circuits to be scanned which can apply to the terminals either potential V1 or V2. The terminals F1, F2, F3 are respectively connected to three sources of impulses which change their potential from VI to V2 at the same frequency but in time units staggered by a third of a period. When the potential of E1 is V1 and that of F1 is V2 (V2>V1) the rectifier Q1 is not conductive and A1 remains at potential V1; when E1 is at V2 and F1 is at V1, Ql is conductive and the resulting current flow from the generator at E1 to that at F1 causes a drop of potential in the'resistance R1 whose value is chosen so that A1 remains substantially at VI. Only when E1 and F1 are simultaneously at V2 is the point A1 brought to V2. In like manner A2 and A3 attain the potential V2 when V2 is simultaneously received on terminals E2, F2 and E3, F3 respectively. The point B is brought to V2 whenever A1, A2 or A3 reaches that potential. If the potentials of the terminals E characterize the conditions of the circuits scanned, the potential at B will successively represent said conditions in a cycle. Scanning device with number of impulse sources less than number of circuits scanned: Fig. 2.-It is assumed that six circuits are to be scanned and these are divided into two groups of three each identical with that of Fig. 1, the output circuits B1, B2 of which are connected to a common point C through rectifiers S<SP>1</SP>1, S'2 respectively. The terminals Fb1, Fb2 are connected to two impulse sources the duration of the impulses. produced by each of which is equal to one complete cycle of successive impulses of the sources connected to Fa1, Fa2, Fa3. Each of the Fb sources characterises one of the groups of circuits. If, for example, E1 and E4 are both atpotential V2 and an impulse V2 is received on Fa1, a long impulse can at the same time be received on only one of the Fb terminals, say Fb1 As the potential received at B1 from E1 is V2 the point B1 assumes the potential V2 which is transmitted via S<SP>1</SP>1 to point C. Terminal Fb2 being at potential V1 and potential V2 being applied to B2 from E4, rectifier Q<SP>1</SP>2 is conductive and the resulting current flow causes a drop in potential in R4 lowering the potential of B2 to VI so that the condition of E4 is not transmitted to point C. The point C thus receives indications of the conditions of the six terminals E in cyclic order, it being possible to scan 100 terminals E in 10 groups of 10 using 10 sources of short impulses and 10 of long. Device for determining the outlet corresponding to an impulse received in the output of a scanning device: Fig. 3.-The output of the scanning device is connected to the point C' (Fig. 3) and the arrangement is such that the paths C<SP>1</SP>E<SP>1</SP>1, C'E'2, ... : C<SP>1</SP>E<SP>1</SP>6 are opened in turn, each when the revelant terminals Fla and F'b are at potential V2 simultaneously. If no impulse is received at C<SP>1</SP> at that time, current flows from the source at BG to the source at C<SP>1</SP>, the drop in potential across the relevant resistor R<SP>1</SP>1 . . . R<SP>1</SP>6 maintaining the corresponding point F<SP>1</SP>1, ... F<SP>1</SP>6 at potential VI. If an impulse is received however (C<SP>1</SP> at V2), it will be passed to the relevant E<SP>1</SP> terminal, the other terminals remaining at V<SP>1</SP>. The potential V2 received on the relevant E1 terminal may produce any desired control or signal. Modification : Fig. 4.-This arrangement differs from that of Fig. 3 in that no rectifiers are included in the paths C<SP>1</SP>E<SP>1</SP>1, ... C<SP>1</SP>E<SP>1</SP>6. If no impulse is received at C<SP>1</SP> the potential at all E<SP>1</SP> terminals is VI since the rectifiers associated with any F<SP>1</SP>a or F<SP>1</SP>b terminal which is at V2 will be non-conductive. If an impulse is received current will flow from C<SP>1</SP> through the relevant resistors R<SP>1</SP>1, ... R<SP>1</SP>6 to the terminals F<SP>1</SP>a and F<SP>1</SP>b which are at V1, reducing the potential at the corresponding E<SP>1</SP> terminals to V1, and only that terminal E<SP>1</SP> of which the terminals Fa and F<SP>1</SP>b are at V2 will receive the impulse. Specifications 716,784 and 707,735 are referred to.