US2447799A - Sequential electronic commutator with supplementary grid control - Google Patents

Description

Aug- 24. li948- A. H. DlcKlNsoN SEQUENTIAL ELECTRONC COMMUTATOR WITH SUPPLEMENTARY GRID CONTROL Filed April 5, 1945 menta Aug. 24,'-1-e4s SEQUENTIAL ELECTRONIC COmTATOl WITH ioll" Y GRID CONTROL mannheim... omni c am to ticnMNew-York, N. Y., a com ration oi New Ascii t. im. serai No. saam This invention relates to electrical systems and particularly to impulse-driven and impulse generating systems capable of' various uses; ior example, as electrical commutatore or the like.

Electronic commutators previously have been devised utilizing electronic trigger circuits of the type having alternate and opposite stable conditions. Such circuit was tripped from either stable condition to the other in response to one driving pulse and tripped back to its former stable condition by another driving pulse.

In contradistinction, the present invention has for an object the provision oi a commutator using trigger circuits each of which is. characterized by only one stable condition.

An object o! the invention is to provide an electronic trigger circuit which has one stable condition and a reverse unstable condition and which must be driven from thestable to thehunstable condition by an impressed impulse but which produces its own impulse for returning the circuit tothe stable condition and wherein a multi-grid tube is provided in one branch of the circuit, such tube having a supplementary-grid which is alterable in potential to control the duration of the unstable status.

In relation to the above object, the invention contemplates the provision oi a common bias adjusting device for the supplemental grids o! all the stages to adjust the self-timed periods of operationof the stages. v

Other objects of the invention will be pointed out in the following description and claim and illustrated in the accompanying drawings, which General description of the commutatore The electronic commutator enables desired results to be aobtained without mechanical inertia and at great speed. The commutator has a number of stages depending on the number of steps through which the commutator is to progress in a single sequence or cycle o! the commutator. The electronic commutators are disclosed'herein to exemplify the invention. As illustrative, each commutator has three stages.

roam (casse-21) Each stage employs and associated impedances and capacity, so interrelatedas to form a novel trigger circuit. This trigger circuit has two alternate states, one ot which is a normal or stable state in which it will remain until driven therefrom by electrical energy-such as an impulse. applied from an external source. The other or reverse state of the 'circuit is an oi-normal or unstable state; i. e.. one vwhich is temporary and from which the circuit automatically switches back. alter a time lapse,` to the stable state. Initially. all the stages o! the commutator are in their stable states. To initiate a cycle of the commutator, a driving impulse will be applied to the ilrst stage to switch it to its unstable status. After a time determined by the electrical constants o! the stage, which may be adjusted in one Vembodiment'. by an external agency, the first stage automatically switches back from its unstable to its stable status.v vIn so doing, the ilrst stage produces a driving iinpulse which is transmitted to the second stage to drive it to its unstable status. The second stage acts similarly to the rst stage, and in returning to its stable status, initiates a reciprocation in status of theA third stage. In the illustrative commutators, the third stage is the last, and ii it is desired to eect only a single cycle of a commutator for each impulse applied to the nrst stage, then the last and ilrst stages are not coupled .to each other. Such commutator may be called a start-stop commutator. It it is desired to provide a continuously operating commutator. the last stage is coupled to the first stage to iorm a closed chain-of circuits. Then. when the last stage switches back to its stable status, it produces an impulse for repeating the reciprocation in status oi the nrst'stage. Repetitive and sequential operation oi the succeeding stages then occurs, and so on in continuous fashion until power is removed from the commutator or until the connection between two of the stages, as the `last and the first, is opened. There are no time The trigger circuit (main form) .This trigger circuit is the basic unit of the com-- mutator shown in Fig. 1. Three such units or stages Si, S2, and S3 are provided for the commutator, as illustrative. Each trigger unit is similar and is shown in a dotted box.

Desired voltage, which may be 300 v. d. c. as indicated, is supplied from a suitable source to the plus line 50 and minus line 5I. A voltage divider 49 across these lines is tapped by a line 52. Preferably, the potential thereby app'ned to line 52 is 60 volts positive with respect to minus line 50. Line 52 may be grounded, as shown.

Since all the trigger circuits in Fig. 1 are alike, a full set of reference characters is applied only to one of them; namely, SI.

Each of these trigger circuits has two impedance networks or branches. One includes resistors 62a, 63a and 64a in series across lines 50 and This impedance network may be considered as including the vacuum tube unit 68h. The other impedance network includes resistor 62h, condenser 65, and resistor 64b in series between lines 50 and 5I. The latter network may be considered as including vacuum tube unit 68a. Umts 68a and 68h may be separate vacuum tubes or may be units of a duplex tube, as shown. The units 68a and 68h may be of the GSC? type. The common cathode of the tube is connected to line 52. The anode of triode 68h is connected to point 66a at the junction of resistances 62a and 63a, while the anode 68a is connected to point 66h which is between resistance B2b and condenser 65. The grid of 68a is connected -to point 61a which is at the junction of resistors 63a and 64a; the grid of 68h is connected to point 61h which is between condenser 65 and resistor 64b. These connections provide cross-coupling between the two impedance networks; that is, each impedance network is coupled to the anode-cathode path of a tube unit which has its grid connected to the opposite impedance network.

Resistances 62a and 64a are equal in value, and each is approximately one-third the value of resistance 63a. The values of any one or more of resistances B2b and 64b and of condenser 65 may be varied in accordance with the desired duration of time for which the circuit is to maintain itself in unstable status. Diierent durations of unstable status were obtained by using different capacities of condenser 65; for example, a condenser 65 with a capacity in the order of .00025 microfarad produced an extremely short duration of unstable status, a condenser 65 with a capacity of substantially .02 microfarad produced a longer duration of unstable status, and a condenser 65 with a capacity of substantially .25 microfarad produced a still longer duration of unstable status. Resistance 62h may be in the order of .1 inegohm and resistance 64b may have a value of substantially 1.1 megohms. Resistances 62a and 64a may each have a value of .1 megohm and resistance 63a may have a value of .3 megohm.

In stable status of the trigger circuit, the grid of triode 68h is substantially at the same potential as minus line 5I since it is connected thereto by resistance 64b. The normal grid bias of 68h is then negative as to maintain Bb at cut-oil. Under this condition, 68h has an impedance relatively high in comparison to that of resistance 62a, and the point 66a, to which the anode of 88h is connected, has a potential which is high with respect to line 52. With resistances 62a, 63a, and 64o properly proportioned, the potential drop across 63a is such as to maintain point 81a substantially at the potential of cathode line 52. Hence, the grid of tube 58a is at zero bias. With the bias of 68a at zero, this tube is highly 4 conductive and has an impedance relatively low as compared to that of resistance 62h. Consequently, point 66h, to which the anode is connected, then has a potential which is not much greater than that of common cathode line 52. Such potential of point 66h has no elect upon the potential of point 61h, inasmuch as these points are bridged by condenser 65. The foregoing describes the stable status of the circuit, in which 68a has maximum current ow, and 68h is at cut-oil', and in which point 66a is at a higher potential, with respect to lines 52 and 5l, than is point 66h. form of the potentials produced at points 66h of the circuits SI, S2, and S3 and shows that points 66h of all the trigger circuits are initially at minimum potential; hence that all the circuits are. initially in stable status. The manner of switching the trigger circuit to unstable status will be described in connection with trigger circuit Sl. It is understood, then, that for the present, the trigger circuit elements referred to below are those of circuit Sl.

With switch 53 in the position shown, it connects one side of condenser 54 to a point on the voltage divider 55, which is between lines 50 and 5I. The opposite side of condenser 54 `is connected to line 5I. The potential of the aforementioned point, of voltage divider 55, to which the condenser is connected is such that the condenser 54 is charged to a potential which is higher than that of point 61a. When switch 53 is shifted to a reverse position from that shown, condenser 54 discharges through resistance 64b. Such discharge is in the form of a sharp positive pulse, and causes point 61h to rise in potential with respect to line 5|. The voltage difference between line 52 and point B'Ib is the grid bias of tube 68h, and the aforementioned increase in potential of point 61h, due to a pulse application, decreases the grid bias of tube 68h sufficiently to cause '68h to start conducting. Current flow occurs from line 50 via resistance 62a and triode Bb to line 52, and causes point 66a to drop suddenly in potential. A related drop occurs at point 61a, increasing the negative grid bias of 68a. Accordingly, current flow through 68a and resistor B2b is decreased, causing point 66h to rise suddenly in potential, producing a positive pulse.

This pulse feeds through condenser 65 to the grid i of 68h, promoting the reduction in negative grid bias of 68h. Such action continues and point 61a is driven considerably below the cut-off potential for triode 68a. The potential of point 66a has now dropped, while that of point 65h has risen to upper value, and the triode 68h is now fully conductive while triode 68a is at cut-off. It is seen that the electrical conditions in the trigger circuit are now reversed with respect to the electrical conditions prevailing in the former status, which is the stable status, of the circuit. As has been described, the circuit was tripped to unstable status by impressing a, positive pulse on point B'lb of the circuit, as a result of which a negative pulse was produced at point 61a of the circuit. It is appreciated that a negative pulse may be impressed directly from an external source upon point 61a of the circuit with the same effect of tripping the circuit from its stable to its unstable status. Such negative pulse applied to point 61a -will drive tube 68a to cut-off, whereby point 66h will rise abruptly to its upper value.

With the point 66h of the circuit at the upper value, the circuit is in unstable status, as is indicated in Fig. 3. The circuit will maintain itself Fig. 3 indicates the generalV I in the unstable status for a chosen interval and will then 'automatically trip itself back to its stable status wherein it will remain until it receives another tripping pulse from an external source. The manner in which and the reasons why the circuit trips itself back from unstable to stable status will now be explained.

As previously described, upon the tripping of the trigger circuit from stable to unstable status, point 66h rose abruptly in potential, and the attendant positive pulse was fed through condenser 65 to point 61h and the grid of triode 58h, reducing its 4grid bias to zero. Stateddiiierently, the rise in potential of point 66h produced a charging current which flowed through condenser 65 and resistor 64b and resulted in an increase in potential of the grid 68h. Depending upon the RC product of the condenser and resistors in the charging circuit, condenser 65 continues to chargeA for a predetermined period of time. The charging current declines in value as condenser 65 becomes more and `more charged. Hence, the grid -potential of triode 68h declines accordingly, whereby the conductivity of this triode gradually declines. Such action is reflected in a gradual increase in thepotential of points 66a and 51a. Eventually, the point 61a rises in potential to such value that the difference in potential between point 61a and cathode line 52 is less than that required to maintain triode 68a at cutoff. Thereupon, triode 68a starts to conduct, and current flow occurs from line 50 through resistances 62h and 68a t line 52. Consequently, point 66h suddenly drops in potential,

' at cut-oir, while tube 68a passes a large amount of current. This stable status is maintained until another pulse is applied to point 61h. When the commutator is conditioned for single cycle operation, the switch 53 must be returned from reverse position to the shown position in order to charge condenser 54, before another pulse can be derived therefrom to start another cycle. But when the commutator is conditioned for repeat cyclic operation, repeat tripping of Si willbe under control of a pulse derived from S3.

The condition of the trigger circuit may be determined by observation of glow discharge tube 56a, which is connected in series with current limiting resistor 51a between line 50 and point 66a. When the circuit is in stable state, point 66a is at a high potential with respect to line 52, and the diierence in potential between this point and line 50 is insufficient to ignite 'tube 56a. ,When

the circuit is in unstable state, the point '66a is i at a low potential, and the difference in potential is great enough to cause tube 56a to fire. Accordingly, whe'ntube 56a is dark, it indicates that the circuit is in stable state. vWhen tube 56a is lighted, it indicates that the circuit is in its unstable condition.

The foregoing has described a stage of the electronic commutator shown in Fig. 1. It is seen at the end or this interval, the stage self-triggers itself back to its stable condition. The length or the interval in which the unstable status is maintained may be varied by varying the electrical constants of the sta-ge; for example, by varying the capacity of condenser 65.

The commutator (main form) This commutator is shown in Fig; 1 and it includes trigger circuits of the kind just described. Since the oommutator is to progress through three steps in a cycle, lit has three stages, trigger circuits SI, S2, and S3. Stage SI is cou pled to stage S2 by a condenser 10 and resistor 1 I extending from point 65h of SI to point 61a of S2. Stage S2 is coupled by a similar condenser and resistor -to stage S3. If the commutator, once started in operation, is to perform repeat cycles automatically, then a switch-12 is closed and a connection is provided from point 6162 of the last stage, S3, via a condenser 10 and resistor I I, the switch 12, and a wire 13 to point 61a of the first stage SI. It is seen, then, that each stage is coupled to .the next by a similar condenser-resistor circuit and that the last stage may be coupled to the rst by a similar circuit which, however, includes a switch for enabling the first and last stages to be disconnected. When this switch, 12, is opened, the commutator will perform only a single cycle for each starting impulse applied to the first stage. The recovery timeof -the condenser and resistor coupling 10 and 1l between each stage and'the next is very small in order that a change in potential at point 56a ol' one stage shall produce a substantially concurrent change in potential at `point 61a of the next stage. Thus, the stages of the commutator are interconnected by coupling circuits which have no time delay circuits and which do not include electronic tubes.`

A11 the stages are `normally in their stable status. In this status of a stage, its tube 68a is fully conductive and point 61a is substantially at cathode potential, ,as previously explained. To initiate operation ofthe commutator, switch 53 is reversed, whereupon condenser 54 discharges a steep positive pulse upon resistor 54h of Si which succeeds in raising the potential of point 61h of SI above cut-off potential. As a result, Si is tripped to its unstable status, as previously described. Point 66h of SI risesv abruptly in potential and the occurrence of this action marks the beginning, D (Fig. 3), of a cycle. It may be mentioned that the rise in potential of 66D (Si) is transmitted by the related condenser and resistor coupling topoint 61a of`-S2. The attendant rise in potential of point 61a of S2 merely coniirms S2 in its stable status.

SI remains in its unstable status for a chosenl drops abruptly in potential and, through the condenser and resistor coupling, a negative pulse is fed to point 61a of S2. This negative pulse is of sufiicient amplitude to trip S2 from its stable to its unstable status, in the manner described before. The simultaneous occurrence of the return of S I to stable status and its tripping of S2 to unstable status defines point 1 of the cycle (see Fig. 3). It is seen that a reciprocation in status of the controlling trigger circuit, Si, effects a single change in status of the controlled trigger circuit,l S2.

S2, likewise, trips itself back to stable status after a chosen interval and in so doing trips S3 to unstable status. This action marks point 2 after a chosen interval and this marks the end of one cycle. If switch 'l2 is open, then a second cycle may be initiated by another initiating pulse received from condenser 54 or any other suitable source outside the commutator. If switch 12 is closed, then the return of S3 to its stable status acts through the coupling circuit to impress a negative pulse upon point 61a' of SI thereby tripping it to unstable status. The simultaneous occurrence of the return of S3 to stable status and its tripping of SI to unstable status marks the beginning of a repeat cycle. Sequential operations will continue until either potential is removed from lines 50 and 5I or until switch 'l2 is opened.

It is seen that the commutator functions sequentially without the use of time delay coupling means between the stages but by the use of stages, comprising trigger circuits, which have self-timing characteristics.

They modification The modification of the commutator is shown in Fig. 2. It is based on a modiiled form of the trigger circuit and is supplemented by means for adjusting thev time duration of the unstable periods of the trigger circuits. Elements of the modication which correspond to elements of the main embodiment are given the same reference characters.

The modied trigger circuit differs from the main form in replacing the triode 63a by a multigrid vacuum tube 69 which, in this instance, is preferably a pentode. In the main form, the duration of time in which the trigger circuit maintains itself in unstable status depends on the vaules of one or more of the resistors 62h and 84h' and of condenser 65. In other words, the unstable period of the main form of the trigger circuit depends on the chosen constants of the circuit itself. In the modied form, shown in Fig. 2, the unstable period depends not only on the chosen constants of the trigger circuit x itself but also on the adjustment of supplementary means which determines thepotential of one of the control electrodes of the multi-grid tube 69. Specifically. the supplemental adjusting means includes a voltage divider 58 between lines 50 and 5| and varying portions of which may be short-circuited by an adjustable switch t0. The point 59 of the voltage divider is connected to a wire 'l5 from which connections are made to the screen grids of the tubes 69 of the trigger circuits Slm, S2m, and 53m of the threestep commutator shown in Fig.- 2. It is seen that the screen potential of a tube 69 may be varied by adjustment of the switch 60.v Thus, with the switch 60 at the spot I, a large portion of voltage divider 58 is short-circuited and the screen potential will be at its lowest value. Adjustment of the switch' to spot 2 will reduce the shortcircuited portion of the voltage divider, and the screen potential will be increased. Further in creases in screen potential may be had by adjusting switch 60 to spots 3 and 4.

The impedance of the pentode is a function of the potentials of the screen and control grids with respect to cathode potential. A rise in screen potential tends to reduce the impedance of the tube. Likewise, a rise in potential of the control grid tends to reduce the impedance of the tube. Thus, if the tube is at maximum impedance or cut-oi! when the screen and control grid potentials are at certain values. it may be maintained at cut-oil.' by suitably reducing the screen potential land lraising the control grid potential or by reducing the control grid potential and raising the screen potential. Conversely, the higher the screen potential, then the, less is the rise requiredin control grid potential to unblock the tube or to driveit to conductivity, whilev a reduction in screen potential will require a greater increase in control grid potential in order to unblock the tube. Thus, by adjustment of switch 60 to raise the screen grid potential, the rise in the control grid potential required to drive the tube to conductivity is lessened to a'related degree. Speciiically, the rise in potential required at point 61a, of a trigger circuit in the modied commutator, in order to unblock the pentode 63 is directly related to the screen potential of th., pentode.

As in the main embodiment, a trigger cicuit of the modified form is in stable status when its tube 88h is at cut-on and its points 86a and 61a are at theirA higher potentials. With point 61a at its higher potential, the control grid potential of tube 69, for any of the possible values oi screen potential, is such as to maintain the tube at maximum conductivity. Upon application oi an adequate positive pulse to point lilb of the circuit or of an adequate negative pulse to point 81a of the circuit, the circuit will be reversed to its unstable status. For instance, a positive pulse may be received by point S'lb of circuit Slm from the condenser 54 when switch 53 is reverd. This pulse will unblock tube 68h and, in consequence, point 66a will drop abruptly in potential. A related drop in potential occurs at point 61a, increasing the negative control grid bias of tube 69. Accordingly, the impedance of tube 68 increases and point 66h rises suddenly in potential,

producing a positive pulse. This pulse feeds through condenser to the grid of 68h, promoting the reduction in impedance of 68h. The ultimate result is that point 61a is driven consideryin value and this is reflected in a gradual decrease in potential of point S'lb. As point 61h declines in potential, the negative grid bias of4 tube 58h increases and the current ow through the tube decreases. Hence, points 66a and 61a of the trigger circuit rise in potential. Eventually the point 61a and, therefore, the control grid potential of tube 69 is raised sufficiently tocause the tube to start conducting. 'I'he potential which point 61a must attain tor` eiect this action-depends on the chosen screen potential. If the screen potential is high, then the potential which point 61a. must attain to drive the tube 69 to conductivity is smaller than when the screen potential is low. Hence, the higher the screen potential, the smaller is the necessary rise in control grid potential and, therefore, the less time it takes for the control grid to attain the required potential. The rise in potential of the control grid is directly related to the time required to charge the condenser 65. Thus. these two factors; one, the adjusted screen potential, and two, the charging circuit constants, determine the length of time elapsing between the tripping of the circuit to unstable status and the driving of tube Il to a conductive status. When tube 69 reaches conductive status, point 66h drops abruptly in potential and the unstable status of the trigger circuit is terminated, the circuit resuming its stable status in the same manner as explained for the main embodiment.

The trigger circuits Sim, Sim, and 83m are interconnected in exactly the same way as the circuits SI, S2, and S3 of the main embodiment. Operation of the modified commutator, therefore, will be similar to that of the main embodiment and as indicated in Fig. 3. It is understood that although the unstable period of each of the stages of either commutator is indicated in Fig. 3 as substantially of equal duration, that the period ductive to establish a stable state of the trigger circuit, self-dissipating reactance means coupling the anode of the second tube to the current controlling electrode of the firsttube so that with of each stage may be adjusted to a different duration than that of any other stage. The rate of commutator operation may be adjusted by varying the constants of the charging circuit of condensers Bland, in the Fig. 2 form of commutator, may also and more readily be adjusted by changing the setting of switch 50.

The sequential operation of either of the disclosed commutators renders available impulses which may be fed to and utilized by controlled circuits for suitable purposes.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied. to two embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated .and in their operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope, of the following claim.

What is claimed is:

' An electronic commutator or the like, comprising a plurality of electronic trigger circuits, eachthe second tube non-conductive the rst tube ,is conductive to denne an unstable state of the trigger circuit from wh ich it returns to the stable state after a chosen time interval, means coupling the output of one of the trigger circuits to the input of the next trigger circuit so that upon return of the former trigger circuit from unstable to stable state it applies a tripping vpulse to the next trigger circuit to reverse it from stable to unstable state for a chosen time interval, a common source of biasing potential for the supplemental electrodes of the plurality of trigger circuits, and adjustable means common to the plurality of trigger circuits for transmitting a variable proportion of the biasing potential to said supplemental electrodes so as to regulate the durations of the unstable intervals of said trigger circuits.

ARTHUR H. DICKINSON.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,050,059 Koch Aug. 4, 1936 2,158,285 Koch c May 16, 1939 2,252,457 Cockrell Aug. 12, 1941 2,272,070 Reeves Feb. 3, 1942 2,306,386 Hollywod Dec. 29, 1942 FOREIGN PATENTS Number Country Date 456,940 Great Britain Nov. 12, 1936 474,739 Great Britain Nov. 8, 1937

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