Patent GB-593577-A (GB)
Title: Improvements in or relating to electronic switching devices
IPC: G06F9/32
Filed: 1944-05-16
Abstract: 593,577. Thermionic distributers; pulse counting circuits. INTERNATIONAL BUSINESS MACHINES CORPORATION. May 16, 1944, No. 9409. Convention date, May 23, 1941. [Class 40 (v)] An electronic hard-valve commutator comprises a closed chain of conductively connected trigger units, each capable of assuming two different electrical conditions. Each unit comprises a pair of reciprocally coupled hard valves with associated electronic control means, whereby the electrical conditions of the units in the chain may be sequentially reversed under the application of a series of electrical impulses, each impulse being applied simultaneously to all the trigger units. The electronic commutator (Fig. 1) comprises the trigger units S1, 2, 3, 4, each consisting of a pair of triode elements 68a, b, and a pair of pentode controlling elements 69a, b, operated by pulses from the multivibrator comprising triode elements 83a, b. Additionally, conditioning valves 91, 106, 104 and switches 90, 95, 100 are provided for the initial operation of the commutator. Electronic trigger unit. A potential divider comprising resistances 56, 57, 58 is connected across the positive and negative supply lines 50, 80, and supplies intermediate potentials to the lines 61, 51. In each unit s1 &c., further potentiometers are connected across the lines 80, 51 and comprise the resistances 62a, 63a, 64a and 62b, 63b, 64b. The resistances 63a, b are shunted by condensers 65a, b respectively, the grids of the triode elements 68a, b being connected to the points 67a, b respectively and the corresponding anodes to the points 66b, a, respectively. Controlling potentials are applied to the control and screen grids of the pentode elements 69a, b whose anodes are connected to the points 66b, a respectively, and whose cathodes together with those of the triode elements 68a, b connect to the line 61. OFF position. If the valve 68b is non-conductive, the potential of the point 67a relative to that of the line 61 is sufficiently positive for the valve 68a to be conductive. The resulting current through the resistance 62b depresses the potential of the points 66b, 67b sufficiently to maintain the valve 68b non-conductive, the control valves 69a, b being normally non- conductive. If the potential of the screening grid of the pentode valve 69b be positive, a positive pulse applied to the control grid will cause it to conduct momentarily, and the resulting drop in potential at the point 66a, communicated through the condenser 65a to the point 67a, causes the valve 68a to become non-conductive. The resultant rise in potential of the points 66b, 67b causes the valve 68b to conduct, thus maintaining the points 66a, 67a at a low potential. This ON position is indicated by the fall in potential at the point 66a causing the gas-discharge tube 78 to strike. Reversal to the OFF position occurs in a similar manner if a positive pulse be applied to the control grid of the pentode valve 69a when its screening grid potential is positive. Negative pulses do not effect a change in the condition of the system, since the valves 69a, bare normally non-conductive. Oscillator (Fig. 1). The multivibrator comprising triode elements 83a, b, cross-connected by condensers 85a, b and resistances 86a, b produces waves of square-top form, from which sharply-peaked pulses mutually 180 degrees out of phase (Fig. 2, a, b) are produced on the lines 75, 76a respectively, by means of condensers 88a, b and potentiometers 72b, a. Electronic commutator (Fig. 1). In each of the trigger units S1 &c., the pentode valve 69b derives its screening-grid potential through a resistance 74 from the centre-tap 77 on the potentiometer resistance 63b of a preceding unit in cyclic order, whereas the screening-grid potential of the valve 69a is derived similarly from the resistance 63b of the succeeding unit. Assume the unit S1 is ON, the units S2, 3, 4 are OFF, and the switch 90 reversed. Then the point 77 (s1) is at high potential and a positive pulse (a, Fig. 2) on the line 75 will cause the pentode valve 69b (S2) to switch the unit s2 to the ON position. The high potential so produced at the point 77 (S2) conditions the pentode valve 69a (S1) so that the succeeding positive pulse (b, Fig. 2) on the line 76a switches the unit S1 to the OFF position. Successive pulses of type a (Fig. 2) on the line 75, and of type b (Fig. 2) on the line 76a, and also produced as described below, on the line 76b, will switch the units S1, 2, 3, 4, &c. on and off in cyclic order and in a similar manner as shown at c. d, e, f (Fig. 2). Commutation may be interrupted at any instant by restoring the switch 90, thus opening the line 75, whilst subsequent reversal of the switch 90 causes commutation to proceed from the stage at which it was interrupted. Conditioning circuits. Since the condition taken up by the trigger units S1, 2, 3, 4 on initial operation is governed by chance, means are provided whereby a selected unit sl may be placed in the ON condition and the remaining units S2, 3, 4 in the OFF condition. Pulses of a type (Fig. 2) from the line 75 are applied to the third grid of a multiple-grid valve 91, the first grid of which is normally connected by the switch 95 to the line 80 and the resultant b type pulses (Fig. 2) produced in the anode circuit are applied over the condenser 97 and resistance 89 to the line 76b. By reversing the switch 95, the pulses from the line 75 are additionally applied to the first grid of the valve 91, the pulses produced in the anode circuit of which are then of sufficient amplitude to trigger any of the pentode valves 69a (S2, 3, 4) irrespective of their screen potentials, and thus place all the units S2, 3, 4 in the OFF position. Pulses of b type (Fig. 2) from the line 76a are applied to the control grid of a pentode element 106, rendered operative by opening the switch 100. The resultant a type (Fig. 2) pulses produced in the anode circuit are applied over a condenser 103 and potentiometer 102 to the control grid of the triode element 104, causing the anode to become momentarily conductive and reduce the potential of the point 66a sufficiently to place the trigger unit S1 in the ON condition. On restoration of the switches 95, 100, and reversal of the switch 90, cyclic operation of the commutator commences. Self-conditioning electronic commutator. In a modification (Fig. 3), the pentode elements 69a, b in each of the trigger units S2, 3, 4 derive screening-grid potentials from the points 77a, b respectively, in the preceding unit, while the elements 69a, b in the unit S1 derive their potentials in reverse order from the points 77b, a respectively, in the unit S4. Pulses of type a (Fig. 4) are produced by the multivibrator comprising the back-coupled valves 83a, b, as described, and are applied over the line 75 to the control grids of all the pentode elements 69a, b. Assume the unit S1 is ON, the units S2, 3, 4 OFF and the switch 90 reversed. Then the points 77a, b (S1) are respectively at low and high potential, so that a positive pulse on the line 75 will trigger the pentode element 69b (S2), thus switching the unit S2 to the ON position. In a similar manner, the following positive pulses can now switch the trigger units S3, S4 in turn to the ON position. Due to the reverse connections, the rise in potential of the point 77b (S4) when the unit S4 is switched ON, conditions the pentode element 69a (S1), so that on the fourth positive pulse the unit Sl is switched OFF. Succeeding pulses now switch off the following units, the eighth pulse completing the cycle by switching the unit S1 to the ON position, due to the reverse connections between the units S4, 1. The instantaneous condition of the elements 68a, b in the chain S1 &c. may be indicated by means of gasdischarge tubes 78a, b connected in the respective anode circuits, and is shown in Fig. 4 (b, c, d, e). The commutator as described is self-conditioning from the initial random configuration on switching on, by the application of the pulses to the line 75.