Patent GB-647811-A (GB)
Title: Improvements in or relating to systems and apparatus for the transmission of data
Inventor: JOHNSON ERIC ARTHUR
IPC: G05D3/12
Filed: 1948-07-21
Abstract: 647,811. Electric follow-up systems. MINISTER OF SUPPLY. July 21, 1948, No. 19567. [Class 40 (i)] In a system for transmitting the angular position of a shaft 1, Fig. 1, the shaft drives means 2, e.g. as described in Specification 653,909, to produce a multi-digital signal representative of the shaft position in coarse fractional divisions of a revolution, and also drives the arm 9 of a potentiometer 7, the tappings on which are energized in a repetitive potential pattern in dependence on the coarse signals so that the voltage tapped off at the arm is representative of the " fine " position of the shaft and is preferably also converted into a fine multi-digital code for transmission. Transmitter. The input shaft 1, Fig. 1, drives a commutator system 2 which defines the shaft position to one part in 512 by means of a nine-digital binary code as in Specification 653,909. The shaft 1 also carries a contact arm 9 movable over a linear potentiometer 7 having 512 equally-spaced tapping points, every fourth tap being connected together and fed through a switch unit 8 from a D.C. source so that the voltage pattern " positive-open circuit-negative-open circuit " is repeated continuously round the potentiometer winding. The switch unit 8, Fig. 6 (not shown), is controlled by the two lowest digits of the 9-digit number developed by the system 2 so that the voltage pattern on the potentiometer is shifted by one tap spacing for every change in the lowest digit of the 9-digit number, and the voltage tapped off by brush 9 is always representative of the shaft position within the appropriate lowest denominational digit of the nine digit number. This voltage is converted at 10 into a seven-digit binary code which is added to the nine-digit code from the system 2 in a circuit 11, Fig. 5 (not shown), which takes care of the overlapping digits from the two sources. Translating potentiometer voltage into binary code, Fig. 4. The unidirectional. voltage V on potentiometer arm 9 is applied at terminal 20 over a resistor 21 to a D.C. amplifier 22 where, in successive positions of a continuouslyrotating switch 26, it is compared with fractions, diminishing in a scale of two, of a stabilized reference voltage R equal to the highest possible value of the input voltage and applied over terminal 25. Thus in the first position of the switch 26, positive at terminal 27 is connected over segment 28 to energize a trial relay 30, in series with a subtractor relay 31. Relay 31 connects the stabilized reference voltage R at terminal 25 over a resistor 33 to feed to the amplifier a potential equal to R/2 in opposition to the input voltage V. If the input voltage V is greater than ¢R, the amplifier output operates a relay 23 which causes a subtractor hold relay 34 to operate and lock in series with relays 30, 31 as the switch arm 26 leaves the segment 28. In the next position 37 of the rotary switch 26 the above-described operations are carried out in a circuit 39 similar to 38 which functions to subtract a potential of “R from the input voltage V. The potential of ¢R is also subtracted if the subtractor hold relay 34 in circuit 38 is operated. In the successive positions of the switch 26 the fractional values R/2, R/4, R/8, &c. diminishing in a scale of two, are thus compared with the remainder of the input voltage after the previous subtraction, and the operated subtractor hold relays 34 in the respective circuits 38, 39, ... represent in the binary system the input voltage. When the rotary switch 26 moves to segment 40, a storage reset relay 41 is energized whereupon in all of the digital circuits 38, 39, ... a storage relay 42 is operated only if the associated subtractorhold relay 34 is unoperated. The operated digital storage relays 42 disconnect the positive supply at terminal 35 from their associated digital output leads 24 which are thereby energized in the binary code according to the potentiometer voltage V. The operated storage relays 42 lock as the rotary switch arm 26 passes to the next segment 48, in which position a relay 32 is energized to reset the relays 30, 31, 34 in all units 38, 39, ... ready for the next rotation of the switch 26. The binary coded output indication on the lines 24 is thus renewed at each rotation of the switch 26, and held for one rotation. Receiver, Fig. 3. The 15-digit binary number may operate the receiver through a servomotor as described in Specification 653,909. Preferably, however, for fine setting, the output shaft 12 carries a contact arm 13 of a potentiometer 14 similar to the transmitter potentiometer, Fig. 1. Coarse and medium units 15, 16 set the shaft through the servo 5 as in the abovementioned Specification in accordance with the first 9 digits of the received code, the two lowest digits of these 9 setting up a potential pattern on the potentiometer 14 through a switch unit 17 in a manner similar to that at the transmitter. The last 7 digits of the transmitted code are reconstituted in a converter 18, e.g. as described in Specification 653,909, to a voltage, and this " fine " voltage is compared with the " fine voltage derived from the potentiometer arm 13 to provide the " fine " error voltage for controlling the servo S.