Patent GB-738001-A (GB)
Title: Binary digital data transmission systems
Inventor: LAWRENCE WALTER
IPC: H03M1/00
Filed: 1952-05-07
Abstract: 738,001. Electric selective signalling. MINISTER OF SUPPLY. May 20, 1953 [May 7, 1952], No. 11592/52. Class 40 (1). Apparatus for generating code groups of binary digit signals, each group giving information on the instantaneous value of a varying quantity which does not vary by more than one code group increment between the generation of successive groups, comprises means for generating a succession of code groups each comprising at least one cyclicprogression code digit signal and a special digit signal of the same significance as that of a given generated cyclic-progression code digit signal and which, as the value of the quantity varies in a given sense, changes its state half out of step with the given cyclic-progression code digit signal at values intermediate between those at which changes occur in the state of this given cyclic-progression code digit signal. Fig. 1 shows in schematic form a telemetering system in which the position of a rotating shaft 2 is kept in step with that of a rotating shaft 1 at a transmitter. A drum 3 attached to the shaft 1 is provided with a number of wires 4, the disposition of which is detected by a coding unit 5 and transmitted to the receiver system. Fig. 2 shows a developed view of one arrangement of the wires 4 on the drum 3. The wires are arranged in six circumferential bands 20-25; bands 21-25 produce a normal five digit set of binary signals D1, D2, D3, D4, D5 respectively, when D1 is the digit of least significance. Band 20 produces a special digit signal DX of the same significance as D but half a step out of phase with D1. The transmitter 7 is arranged to sample and transmit outputs from detector 5 in the order DX, D1, D2, DX, D1, D3, DX, D1, D4, DX, D1, D5, DX, D1, D2; the receiver system stores these signals and interprets them so that the shaft 2 is kept in the correct position. In an alternative arrangement, Fig. 3 (not shown), the special digit signal is of the same significance as D2 but half out of phase with D2. The rules for interpreting the output of the transmitter are: (1) If D1 has changed since the last three digit code group no other digit will have changed; (2) If DX has changed one of the other digits will have changed, namely DR if D(R-1)=1 and each of D1- D(R-2)=0 or D5 if D1-D3 are all zero whatever the value of D4; (3) Any digit other than DX or D1 cannot be changed in two successive code groups. Fig. 7 shows a circuit for applying these rules comprising 6 trigger circuits TX and T1-T5 which correspond to digits DX and D1-D5. Each of these trigger circuits comprises a double-triode provided with a 1 (mark) input and a 0 (space) input. Any change in trigger TX results in a positive pulse being applied to the grid of valve VSa, thus producing a negative pulse on its anode which is connected by leads L2 to L5 through rectifiers WX2 to WX5 to triggers T2 to T5. Leads L2 to L5 are also connected to triggers T2 to T5 through further rectifiers to ensure that the state of any of these triggers cannot be changed unless each of the triggers two or more below in significance are in a 0 state, which is when the left-hand valves are conducting. The right-hand valves of triggers T2-T4 are connected through resistances to L2 to L4 to ensure that a trigger cannot be changed over unless the trigger storing a digit of immediately lower significance is in a 1 state. Thus these connections ensure that rule 2 is carried out. To carry out rule 3, each of the anodes of trigger T2-T5 is connected to a lead LX so that when a trigger changes its state a positive pulse is transmitted along LX to the grid of valve VSb to maintain it conducting for one and a half digit periods; VSa is therefore prevented from conducting so that a change in any of triggers T2-T5 cannot take place in a digit period following that in which one of the triggers has changed its state. Specification 717,114, [Group XIX], is referred to.