Patent GB-692817-A (GB)
Title: Improvements relating to apparatus for indicating or recording instantaneous values of variable magnitudes
IPC: H03M1/00
Filed: 1950-12-21
Abstract: 692,817. Electric selective signalling. LITTLE, Inc., A. D. Dec. 21, 1950 [Jan. 14, 1950], No. 31137/50. Class 40 (i). Periodic samples of the magnitude of a direct voltage representative of any variable are converted to and indicated or recorded in the binary system. In a first discriminator stage each sampled magnitude v is compared with a fixed voltage, say p. If v is less than p it is passed unchanged to the next stage where it is compared with p/2. If, however, v is greater than p, a relay in the first stage is operated and passes (v-p) to the second stage for comparison with p/2. The second and subsequent stages function similarly to stage one, each stage say the rthcomparing the input voltage with a voltage p/2r 1 corresponding to the rth binary digit represented by the stage and passing on the input unchanged, or less by p/2x-1, to the next stage. The operated relays in the various stages then represent the magnitude v in binary form and may be indicated or recorded on a punched card before the stages are zeroised ready for the next sampling. The number of stages is limited by the noise level in the system which determines the comparison voltage in the last stage. The invention may be used, e.g. for measuring sample ordinates of graphs converted to a voltage by a photomultiplier tube. Discriminator stages, Figs. 1, 2. Each stage, Fig. 1, may consist of a triode 10 normally blocked by a biasing battery 12 or other source of voltage p. If the input voltage v applied to the earthedscreened line 13 is greater than p then the triode conducts. and a relay 16 in its anode circuit operates to pass the grid voltage, i.e. (v-p) over line 21 to the next stage. If, however, v is less than p then v is passed unchanged direct to line 21. Preferably, two relays 41, 33 are used in each stage as shown in Fig. 2. Here, relay 33 in the anode circuit of the gas tetrode 25 operates if the input v is greater than the bias voltage p of battery 23. The relay 41 is preferably actuated by a timer and, when operated, passes the input voltage unchanged to the output 38 if v is less than p. If, however, v is greater than p the tube 26 fires and the difference voltage (v-p) is passed to the output 38 independently of relay 41. Hard tubes connected "flip-flop" fashion may be used instead of the gas tetrode 26, or transistors may be used. Sampling, Fig. 3. The variable input voltage v is applied at 13 to a cathode follower 140, the output from which at 53 charges a condenser 57 to a corresponding voltage. The charging cicuit is completed by a relay 56 at the start of each conversion cycle, the relay being energized for a short period to enable the condenser to be fully charged and then de-energized for the remainder of the cycle. The condenser voltage proportional to v remains constant for the duration of the cycle and is applied through a further cathode follower 60, line 67, and a compensating battery 69, Fig. 4, to counteract the steady current from the tube 60 to the first discriminating stage 68a. At the end of the cycle the condenser is discharged over a resistor 65 so as to be ready for the next sampling at the, start of the next conversion cycle. Analogue, to binary conversion cycle At the start of a cycle the sampling relay 56 is energized over a microswitch 144 and line 130. Relays 119, 120 are simultaneously energized but are delayed in operation by a condenser 122 in parallel therewith to give the sampling condenser time to charge. When relay 120 pulls up it de-energizes the sampling relay 56, and relay 119 applies H.T. from line 52 over line 74 to timing relays 72a, 72b ..... 72f and to the discriminator stages 68a, 68b ..... 68g, Fig. 4. The first timing relay 72a is energized immediately from line 74 in series with the timer relay 41a in the first discriminator stage 68a, and causes sequential operation of the timer relay chain 72b ..... 72f, each of these relays operating in series with the corresponding timer relays 41b ..... 41f in the successive discriminator stages. The various discriminator stages, except the last 68g, are similar to the Fig. 2 arrangement, gas tetrodes 26a ..... 26g and the relays 33a ..... 33f in the successive stages being operated or not according to whether the stage input voltage is greater or less than the stage bias voltage 23a ..... 23g. Relays 83a ..... 83f, Fig. 5, are series connected with the respective stage relays 33a .....33f so that the operated relays of either of these two sets of relays represent in binary form the sampled voltage magnitude. A further relay 103, Fig. 3, is energized in series with the timer relays 72d, 41d and connects a relay 76 across a normally charged condenser 108 which is so dimensioned that the relay 76 pulls up only after the succeeding timer relays 72e, 72f have operated to complete operation of all the discriminator stages, and complete the discharge circuit of the sampling condenser 57 at 82f. Relay 76 effects recording of the binary number and mechanically throws the microswitch 144 to de-energize relays 119, 120, When the condenser 108 has discharged sufficiently to release relay 76 the microswitch returns to normal and disconnects H.T. + ve from line 74 whereupon the timer relays and discriminator stages revert to normal and sampling relay 56 energizes to effect sampling for the next cycle. Indicating and recording. Those of the relays 83a ..... 83g, Fig. 5, energized according to the magnitude of the sampled voltage extend + ve from line 89 to corresponding contacts 100a ..... 100g of a punching mechanism which is operated to punch corresponding holes in a record card when relay 76 pulls up to extend + ve to contact 102. The binary number is indicated on neon tubes 96a ..... 96g by throwing a switch 92 when the indicator tubes associated with operated relays 83a ..... 83g light. Modifications. The biasing voltages in the discriminator stages may be obtained electronically. The apparatus instead of being " selfcycling" as above described may be cycled manually or by further control mechanism.