Patent GB-722519-A (GB)
Title: Arrangement for the conversion of voltages of analogue form into binary codes and vice versa
Inventor: OBERMAN ROELOF MAARTEN MARIE
IPC: H03M7/00
Filed: 1951-10-23
Abstract: 722,519. Electric selective signalling. STAATSBEDRIJF DER POSTERIJEN TELEGRAFIE EN TELEFONIE. Oct. 23, 1951, No. 24782/51. Class 40 (1)  An electronic arrangement for converting the analogue value of a signal voltage into binary form, and vice versa, comprises  flip-flop electronic trigger devices, one for each binary system denomination, and each of which takes constant anode current regardless of which tube is conducting in each trigger device. The analogue signal voltage is applied simultaneously to the control grids of either the " zero " or " one tubes, in all the trigger devices, and the anode loads are so connected and the control grids so biased that application of any one signal voltage operates a predetermined one of the trigger devices; has no effect on higher denominational trigger devices, but automatically sets all the lower denominational devices according to the binary value of the applied signal voltage. Fig. 1 shows similar trigger devices A, B, C, - - - - - - corresponding to the n<SP>th</SP>, (n-1)<SP>th</SP>; ... binary system denominations, the various elements associated with the respective denominations being distinguished by the prefix letters A, B, C, &c. Each device consists of tubes B1-B2 connected flip-flop fashion, the tube anodes being connected through load resistors R2, R4 across individual resistors AR3, BR3, CR3, - - - - forming a potential divider, and having resistance values in the ratio 2<SP>n</SP>, 2"-', --- 8, 4, 2, 1. The grids of the tubes B2 are connected to points AP1, BP1 - - - on potential dividers R1-R6, the positive ends of which are connected to points on the divider AR3, BR3. ----. The points AP1, BP1, - - are thus biased at successively decreasing positive potentials so that all the tubes B2 conduct in the absence of any input signal. A constant current tube B3 in each trigger device is series connected with the conductive tube of its associated pair B1-B2 to ensure that each trigger device takes a constant anode load current. The anode current of each trigger device flows through the resistors AR3, BR3 - - - - - of the higher denominational trigger devices, but flows through its individual resistor AR3, BR3 - - - only when the " zero " tube B2 is conducting. Thus the positive signal voltage, applied over'X to the control grids of all the tubes B1, will actuate the highest denominational trigger device where the applied signal on tube B1 exceeds that on the grid of tube B2 by a predetermined amount. The anode current of the trigger device in question will now not flow through the associated resistor R3 thereby increasing the grid potentials of the B2 tubes of the lower denominational trigger devices, which in a similar manner will set themselves in accordance with the comparison of the signal voltage on their B1 tube and the bias voltage on their B2 tube, and modify the bias on tubes B2 of succeeding devices. The binary stages are thus set according to the analogue value of the applied voltage. The zero state of the binary coder may, conversely, be taken as that in which all the B tubes are fired in which case the signal voltage must be negative. In a modified arrangement, Fig. 3, the signal voltage is applied over point X to the grids of the B2 tubes of all denominational devices by way of individual potentiometers AR6-AR7, BR6-BR7, - - - and the grids of the B1 tubes tapped to points on individual potentiometers AR8-AR9, BR8-BR9 across the respective anode supply to the associated elements. The system functions similarly to the Fig. 1 arrangement except that the signal voltage is negative in this case. A converse arrangement may be used with this Figure as stated above for Fig. 1 in which case positive signal voltages are used. Modifications. A signal amplifying stage, Fig. 4 (not shown), may be used with each trigger device, and by adding the arrangement of Fig. 5 to the coder any binary indication resulting from an applied signal voltage may be held after the signal voltage has been removed. The resistors AR3, BR3, - - - of all the binary denominational devices (Fig. 1 or Fig. 3) are connected in series with a potentiometer Rl, Fig. 5, across the anode supply whereby the grid of a pentode B5 is maintained at a potential which varies in discrete jumps proportionally to the signal voltage. The tube output voltage, which varies correspondingly, is fed over. a cathode resistor R6 in the case of Fig. 1, or over an anode resistor RS in the case of Fig. 3, to the signal input point X and is arranged to be equal to the signal voltage so that when the latter is removed the equal holding voltage from BS holds the indication. To stabilize the code, particularly in the case of speed current sampling, the analogue voltage amplitude may be increased or decreased slightly in a manner not shown, to ensure that the various binary coder denominational devices are not unstable. Binary to analogue conversion, Fig. 6. The binary code is set up on denomination trigger devices A, B, C, - - - by applying the input code pulses sequentially to the inputs of the respective denominational devices. Normally, i.e. at zero reading, tubes B are conductive, the " one " tubes B2 firing when an input pulse is fed to the corresponding denominational trigger device. Each reading is held until the trigger devices are all reset by a reset impulse to the B1 tubes. The potentiometer chain of resistors AR3, BR3, CR3 - -- have in this case resistors of ratio 1: 1: 2: 4: 8: - - - 2<SP>n-2</SP>, in which case the potential at the lower denominational end of the resistor chain is an analogue measure of the binary value. Specification 655,369 is referred to.