Patent GB-642656-A (GB)
Title: Improvements in or relating to thermionic valve commutators or the like
IPC: G06F9/32
Filed: 1947-02-28
Abstract: 642,656. Pulse counting circuits. BRITISH TABULATING MACHINE CO., Ltd. Feb. 28, 1947, No. 5896. Convention date, March 1, 1946. [Class 40 (vi)] A thermionic commutator comprising a number of hard valve trigger circuits which also form pulse gates, can be set up so that the pulse gates open in any one of a number of predetermined sequences, and is characterized by means reacting to the pulse passed by the last gate to open in the cycle, whereby all the gates are closed concurrently. The commutator comprises a pulse generator M, a startstop control circuit T, circuits SA and SAX controlling the direction of operation, and a number of trigger gate circuits C1-4. Pulse generator. A multivibrator M generates a square waveform from which switching impulses are obtained by differentiation in networks comprising condensers 75a, aa, b and resistances 76a, aa, b respectively. A valve 86 operating with grid current bias suppresses positive-going pulses in the differentiated train applied to its grid and inverts negative-going components to positive impulses on the line 123, while valves 84, 118 which are biassed to cut-off respond only to positivegoing components and provide negative impulses on the lines 122, 124 respectively 180 degrees out of phase and in phase with the pulses on line 123. Start-stop and direction controlling circuits. The circuits T, SA and SAX comprise trigger gate circuits of the type described in Specification 632,212 in which the screens and control grids of a pair of pentode valves are crosscoupled to form a trigger circuit and the anodes and suppressor grids are used as pulse gates under control of the trigger action. In off status valve 95b alone conducts, anode current flowing under control of the suppressor potential, while in on status 95a is the conductive valve ; reversal is obtained by applying tripping impulses to the control grids, a positive pulse being applied to a non-conductive valve or alternatively a negative pulse to the conductive valve of a pair. Trigger gate circuits. The circuits C1-4 are a modification of the above-described trigger circuit in which a triode valve replaces the pentode 95b, this arrangement providing only a single gate. Thermionic commutator. The commutator may be operated in a forward sequence, the stages C4-1 being switched on in turn, all finally being switched off concurrently, or in the reverse sequence. Forward commutation may be commenced at any stage as chosen by interconnection of sockets Fc and F4 &c., and may be terminated at any stage as chosen by FTc and FT4 &c. Sockets FP are linked in pairs and enable each stage to control the one to its right ; any stage may be cut out of the cycle by linking across it. Corresponding sockets R, RT and RP provide for reverse operation. For forward operation the circuits SA, SAX are tripped to on status by means of a negative pulse from a source (not shown), applied over condensers a or by a positive pulse over condensers b, while for reverse operation the circuits are tripped off by pulses of opposite sign. The chosen cycle is started by reversing a switch 116, which discharges condenser 117 and applies a positive impulse to the grid of 95a (T) switching the circuit T on. With 95a (T) conductive, a negative pulse on the line 124 is inverted to a positive pulse on line 147 which produces a negative impulse at the conducting anode of circuit SA ; this impulse passes over the chosen connections F or R and switches on the selected starting stage C1 &c. The remaining selected stages are then switched on in turn by successive impulses on the line 123, as inverted and transferred from stage to stage over the chosen connections FP or RP. The final stage to be switched on produces a reduced bias on the control grid of a pentode 131 or 141 to which it is connected via sockets FT or RT, according as forward or reverse operation has been chosen. The selected pentode is then enabled to invert the following negative impulse applied to its suppressor grid from line 122 to a positive anode circuit impulse which is again inverted by circuit SAX. The negative pulse so produced is transferred over line 160 and switches circuit T to off its pentode 95b is then conductive and inverts the following positive impulse on the line 123 to a negative impulse which is transferred over line 161 to the grids of all pentode elements in circuits C1 to 4, switching them off concurrently' The cycle is now completed and reversal of switch 116 is again necessary to repeat it. The Specification also describes interconnections which may be used to obtain combined forward and reverse operation of the commutator, in which one of the intermediate stages C2 or 3 is first switched on and is followed bv simultaneous operation of both the adjacent stages, the remaining stage being subsequently operated or omitted from the cycle.