US2431705A - Electrical timing arrangement - Google Patents

Description

Dec. 2, 1947. A. NEMET ELECTRICAL TIMING ARRANGEMENT Filed July '7, 1944 I TIME.

EB ANTHONV NEME? Attorney Patented Dec. 2, 1947 UNITED STATES ELEGTRICAL TIMING ARRANGEMENT Application July 7, 1944, Serial No. 543,929 In Great Britain May 18, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires May 18, 1963 8 Claims. 1

The present invention relates to electrical timing arrangements and is more particularly concerned with arrangements for ensuring that a circuit to be controlled is closed for a predetermined time which may be of the order Of a fraction of a second. Such equipment may find advantageous application for instance in X-ray technique or for the control of arc welding. In such circumstances it is most important that the period in question should be accurately determined, should preferably be adjustable and in some cases, since it may be so small as to involve only a few cycles of the supply current, shall have its commencement and end bearing a definite phase relationship to the supply, or in other words the closure and re-opening of the circuit must take place at a definite point in the cycle. The chief object of the invention is to provide an arrangement whereby the various requirements are met in a simple manner.

According to the invention in an electrical timing arrangement for effecting the completion of a circuit for a predetermined time, a gridcontrolled gas discharge full wave rectifier system is provided with separate starting and stopping circuits which are applied to the same grids of the rectifier. Preferably the starting circuit includes a direct current leak with means for superimposing a phase-controlled ripple, and the stopping circuit comprises a grid controlled gas discharge tube and a timing circuit.

The invention will be better understood from the following description of one method of carrying it into eiiect which should be taken in conjunction with the accompanying drawings in which Fig. 1 shows the circuit diagram, Fig. 2 shows the voltage-time relationships for the applied and critical values of the grid bias on the valves of the full wave rectifier of Fig. 1 and Fig. 3 shows a modificat on of the circuit of Fig. 1. From Fig. 1 it will be seen that the main circuit M is opened and closed under the control of a relay RE which is connected in the anode circuits of the tubes VI and V2 which are arranged to rectify alternate half-cycles of the alternating current supply, so that the direction of current flow through the relay is always the same. The tubes VI and V2 are grid-controlled gas discharge tubes of known construction for instance of the argon-filled or mercury vapour type, the property of which is that once the tube has be come ionized owing to the application of a suitable potential to the grid, it can only be extinguished by reducing the anode voltage to zero and is independent of subsequent variation of the grid potential.

The tube V3 in the control circuit is also of the grid-controlled gas discharge type though its characteristics need not be identical with those of tubes VI and V2. The main supply which may be 50 cycle alternating current of ordinary commercial voltage and may also feed the circuit to be controlled is applied between the terminals 1 and 2 to the primary of a transformer pro vided with two centre-tapped secondary windings TI and T2. The winding Tl serves to supply anode potential to the tubes VI and V2 whereby the relay RE is energised when one or other of the tubes is conducting. The winding T2 is connected to one diagonal of the bridge network comprising the fixed condensers C2 and G3 which are of equal value and the adjustable resistances R8 and R! which are ganged so that their resistances are altered together. The opposite diagonal of the bridge extends to a rectifier Q which is so poled that the pulsating direct voltage between point I which is connected to the center top of the winding T2 and point 8 which is connected to the output of the rectifier Q is such that point 5 is negative with respect to point 7. PI is a potentiometer connected between points 3 and 4 to which a source of direct current is connected. This is shown as a battery but it may alternatively be provided by rectification from the supply with smoothing if necessary.

The normal position of the apparatus is as shown with the control switch S closed. In these circumstances all the tubes are inoperative, and condenser C4 is charged from the source 3-4 through the switch S. The total negative potential existing between the grids and cathodes of the tubes VI and V2 is thus constituted by the negative potential derived from the rectifier Q and existing between point 8 connected to the grids of tubes VI and V2 and point I and by the potential across condenser G4 which is connected in series with the potential derived from rectifier Q and which exists between the point 7 and the cathodes of the tubes. The potential which is across condenser C4 and which is inserted in the grid circuit of the tubes VI and V2 is greater than the amplitude of the pulsating negative potential between points 1 and 3. Hence the potential of point 9 connected to the grids of tubes VI and V2 is sufiiciently negative with respect to point 3 connected to the cathodes of these tubes as to prevent them from striking.

Qondenser CI in the circuit of the tube vs is charged from the potential between points i and 6, one terminal of the condenser being connected to the cathode of tube V3 and to point ii and the other terminal of the condenser being connected at point 5 to the grid of tube V3 through the resistance R2 and to point 4 through an auxiliary contact on the relay RE. Since the point 4 has a negative potential with respect to point 6, the grid of tube V3 is therefore negative with respect to its cathode.

The closing of the main circuit M for a predetermined short time is initiated by opening the switch S. When this is done, condenser C4 discharges through resistance R8 and the negative grid potential component contributed by the voltage across condenser C4 is therefore removed from point 9. Consequently, when the pulsating potential applied from the bridge network through the rectifier Q reaches an appropriate figure, probably substantially zero, the grid bias on the grids of the tubes VI and V2 will intersect the critical bias curve of either valve and thus cause ignition. This can readily be understood by reference to Fig. 2 in which a curve a represents the critical grid biases on both tubes as a function of the anode voltage applied by the transformer winding TI, curve b the actual grid bias common to both grids, curve the D. C. component of curve b. The rate of decline of c is governed by the values R8 and C4. It is obvious from Fig. 2 that the intersection point of a, and b occurs at a minimum of curve b. The phase relationship of this intersection point with curve a is governed only by the ripple on curve b the phase position of which can be adjusted by the phase shifting device R6, R7, C2, C3. The point of intersection of curves a and I; does not depend on the instant of opening switch S. The critical grid bias relationship shown by curve a depends on the characteristics of the tubes and their anode voltage. The ignition will take place on that tube having positive anode voltage at the instant of intersection of the curves a and b. Consequently the precise instant at which the striking of VI and V2 takes place can be controlled with a fine degree of precision and assuming the main circuit M interconnecting the supply lines and the apparatus to be controlled is connected to the same supply lines to which the terminals l-2 are connected the particular point in the cycle at which this circuit is closed can also be controlled. When one of the tubes VI or V2 is conducting a fiow of grid current occurs by way of resistances R3 or R4 and R5 thereby imparting to the point 9 a potential approaching the potential of the cathodes of tubes VI and V2 and hence of the point 3, the negative potential initially applied to the said grids from the restifier Q at the point 8 being taken up largely through the resistor R5. The effect of this is that as one tube is extinguished due to the reduction of the anode voltage to zero the other tube immediately strikes regardless of the potential applied at the point 8.

As long as these conditions persist therefore, pulsating current flows through the winding of the relay RE and is suilicient to cause its operation. This relay closes the main circuit and by means of the contact I 0 thereof opens the connection between points 4 and 5. The opening of the connection between points 4 and 5 allows the condenser CI to discharge through the resistor RI. The time required for this to take place may be varied by adjusting the value of the resistance RI. In due course the potential across condenser CI and hence the negative potential on the grid of tube V3 is reduced sufliciently to enable the tube to strike, the anode of tube V3 being at a positive potential relative to the cathode by reason of the above pointed out conduction in the grid circuit of tubes VI and V2. The conduction through the tube V3 causes the point 9 to assume a potential approaching the potential of point 6 so that the potential of point 9 suddenly becomes negative with respect to point 3 and consequently the valves VI or V2 will extinguish in order when the potentials applied to the respective anodes become zero. As a result the energising current for the relay RE is cut off and it releases, thereby opening the main circuit and again closing the charging circuit for condenser CI. The tube V3 is extinguished when tubes VI and V2 no longer pass grid current and the conditions are thus restored to the original state.

If only a single impulse is required as is usually the case in X-ray work, it is arranged that the switch S is again closed before the tube V3 strikes. This closing has no adverse effect on the operation since resistance R5 which is of the order of one megohm is sufiicienty high to prevent the re-imposition of the suppression potential being efiective as long as the tubes VI and V2 are in action.

The switch (shown in Fig. 1 as the switch S) for initiating the timing circuit may be in the form of a relay contact SI of a relay RE2 as shown in Fig. 3. Relay REZ is energized by a battery or other source B through a normally closed contact I I of the relay RE and the normally open switch S2. Upon closing the switch $2 the relay RE2 becomes energized thereby opening the contacts SI and initiating the timing cycle above described with reference to Fig. 1 said cycle including also the opening of the contact Iii of relay RE as previously described and the opening of the contact II. The opening of the contact II deenergizes the relay RE2 causing the contact SI thereof to close. By holding switch S2 in the closed position contact SI is intermittently closed by the contact II and the cycle of operation is thus repeated automatically. Such an arrangment is particularly suitable for controlling spot welding apparatus.

It will thus be seen that according to the invention a simple arrangement using tubes of well-known commercial type has been devised whereby circuits can be closed for small time intervals with high precision and the closures being adjusted to the phase of the supply circuit so as to obtain the most favorable results for the purpose in hand.

I claim:

1. An electrical circuit arrangement comprising a gaseous discharge tube having a cathode, a control grid and an anode, means to apply an alternating potential between said cathode and said anode, a source of a constant amplitude and unidirectional voltage, a source of a variable amplitude unidirectional voltage, means to connect the voltages of said sources in series relationship between the said cathode and control grid to thereby apply a negative potential to said grid and maintain said tube in its non-conductive condition, means to disconnect said constant amplitude voltage source from said series circuit to thereby reduce the amplitude of the negative potential applied to said grid and initiate conduction in said tube, means in the series circuit between said cathode and said grid to reduce the amplitude of the said variable amplitude voltage applied to said grid during conduction in said tube, and a timing element actuated by the current flow in said tube and coupled to said grid to apply a negative potential to said grid and thereby return the tube to its non-conductive condition after a predetermined interval of current flow in said tube.

2. An electrical circuit arrangement comprising a gaseous discharge tube having a cathode, a control grid and an anode, means to apply an alte atin potential between said cathode and said anode, a source of a constant amplitude unidirectional voltage, a source of a unidirectional voltage having amplitude variations in synchronism with the amplitude variations of said alternating potential, means to connect the voltages of said sources in series circuit relationship between the said cathode and control grid to thereby apply a negative potential to said grid and maintain said tube in its non-conductive condition, means to vary the phase of the variations of said variable amplitude voltage, means to disconnect said constant amplitude voltage source from said series circuit to thereby reduce the amplitude of the negative potential applied to said grid and initiate conduction in said tube at a time determined by the phase of the variations of said variable amplitude voltage, means in the series circuit between said cathode and said grid to reduce the amplitude of the said variable amplitude voltage applied to said grid during conduction in said tube, and a timing element actuated by the current flow in said tube and coupled to said grid to apply a negative potential to said grid and thereby return the tube to its non-conductive condition after a predetermined interval of current flow in said tube.

3. An electrical circuit arrangement comprising a gaseous discharge tube having a cathode, a control grid and an anode, means to apply an alternating potential between said cathode and said anode, a source of a constant amplitude unidirectional voltage, a source of a variable amplitude unidirectional voltage, means to connect the voltages of said sources in series circuit relationship between the said cathode and control grid and to thereby apply a negative potential to said grid and maintain said tube in its nonconductive condition, means to disconnect said constant amplitude voltage source from said series circuit to thereby reduce the amplitude of the negative potential applied to said grid and initiate conduction in said tube, means in the series circuit between said cathode and said grid to reduce the amplitude of the said variable amplitude voltage applied to said grid during conduction in said tube, and means to apply a negative potential to said grid and thereby return the tube to its non-conductive condition after a predetermined time interval, said latter means comprising a discharge tube having a cathode connected to an intermediary voltage point of said constant amplitude voltage source, a grid connected to a point or said source at a negative potential relative to the said intermediary point and an anode connected to the grid of said gaseous discharge tube, a condenser and a resistor connected in shunt relationship between the oathode and grid of said second discharge tube and a switching element responsive to current flow in said first discharge tube to disconnect the grid of said second discharge tube from said source of constant potential.

4. An electrical circuit arrangement compris- *6 ing'two gaseous discharge "tubes each having a cathode, a controlgrid and an anode, an alternating potential source between the cathodes and the anodes for energizing the anodes in phase opposition, a common cathode grid circuit for said tubes comprising a condenser and a resistor connected in shunt relationship and a source of a variable amplitude-unidirectional voltage connectedin series with the condenser and resistor and having its negative pole connected to the grids of said tube, a source of a constant amplitude unidirectional voltage for charging the'condenser in phase with the variable amplitude voltage to thereby "maintain said tubes in a non-conductive condition, means to disconnect said constant amplitude voltage source from said condenser to thereby reduce the'negative potential applied to said grids andiiniti'ate conduction in said tubes, means interposed between said grids and said variable amplitude voltage source to reduce the amplitude of said variable amplitude voltage applied to said grids during conduction in said tube, and a timing element actuated by the current flow in said tubes and coupled to said grids to apply a negative potential to said grids to return the tubes to a non-conductive condition after a predetermined interval of current flow in said tubes.

5. An electrical circuit arrangement comprising two gaseous discharge tubes each having a cathode, a control grid and an anode, an alternating potential source between the cathodes and said anodes for energizing the anodes in phase opposition, a common cathode grid circuit .for said tubes comprising a condenser and a resistor connected in shunt relationship and a source of a variable amplitude unidirectional voltage connected in series with the condenser and resistor and having its negative pole connected to the grids of said tubes, a source of a constant amplitude unidirectional voltage for charging the condenser in phase with the variable amplitude voltage to thereby maintain said tubes in a nonconductive condition, means to disconnect said constant amplitude voltage source from said condenser to thereby reduce the negative potential applied to said grids and initiate conduction in said tubes, a resistor interposed between said grids and said variable amplitude voltage source, and a timing element to apply a negative potential to said grids and thereby return the tubes to their non-conductive condition after a predetermined interval or current flow in said tubes, said timing element comprising a third discharge tube having a cathode connected to an intermediary voltage point of said constant amplitude voltage source, a grid connected to a point of said source at a negative potential relative to said intermediary point and an anode connected to the grids of said gaseous discharge tubes, and a switching element responsive to current flow in said first discharge tubes to disconnect the grid of said third discharge tube from said source of constant potential.

6. An electrical circuit arrangement comprising two gaseous discharge tubes each having a cathode, a control grid and an anode, an alternating potential source between the cathodes and the anodes for energizing the anodes in phase opposition, a common cathode grid circuit for said tubes comprising a condenser and a resistor connected in shunt relationship and a source of a variable amplitude unidirectional voltage connected in series with the condenser and a resistor and having its negative pole connected to the grids of said tubes, a source of constant amplitude unidirectional voltage for charging the condenser in phase with the variable amplitude volt age to thereby maintain said tubes in non-conductive condition, means to disconnect said constant amplitude voltage source from said condenser to thereby reduce the negative potential applied to said grids and initiate conduction in said tubes, a resistor element interposed between said grids and said variable amplitude voltage source, and means to apply a negative potential to said grids and thereby return the tubes to their non-conductive condition after a predetermined time interval, said latter means comprising a third discharge tube having a cathode connected to an intermediary voltage point of said constant amplitude voltage source, a grid connected to a point of said source at a negative po tential relative to said intermediary point and an anode connected to the grids of said gasecus discharge tubes, a condenser and a resistor connected in shunt relationship between the cathode and grid of said third discharge tube, and a relay switching element responsive to current flow in said gaseous discharge tubes to disconnect the grid of said third discharge tube from said source of constant potential.

7. An electrical circuit arrangement comprising two gaseous discharge tubes each having a cathode, a control grid and an anode, an alternating potential source between the cathodes and the anodes for energizing the anodes in phase opposition, a common cathode grid circuit for said tubes comprising a condenser and a resistor connected in shunt relationship and a source of a unidirectional voltage having amplitude variations in synchronism with the amplitude variations of said alternating potential connected in series with the condenser and resistor and having its negative pole connected to the grids of said tubes, a source of a constant amplitude unidirectional voltage for charging the condenser in phase with the variable amplitude voltage to thereby maintain said tubes in a non-conductive condition, means to vary the phase of the variations of said variable amplitude voltage, means to disconnect said constant amplitude voltage source from said condenser to thereby reduce the negative potential applied to said grids and initiate conduction in said tubes at a time determined by the phase of the variations of said variable amplitude Voltage, a resistor element interposed between said grids and said variable am plitude voltage source, and means to apply a negative potential to said grids and thereby return the tubes to their non-conductive condition after a predetermined time interval, said latter means comprising a third discharge tube having a cathode connected to an intermediary voltage point of said constant amplitude voltage source, a grid connected to a point of said source at a negative potential relative to said intermediary point and an anode connected to the grids of said gaseous discharge tubes, a condenser and a resistor connected in shunt relationship between the oathode and grid of said third discharge tube, and a relay switching element responsive to current flow in said gaseous discharge tubes to disconnect the grid of said third discharge tube from said source of constant potential.

8. An electrical circuit arrangement comprising two gaseous discharge tubes each having a cathode, a control grid and an anode, an alternating potential source between the cathodes and the anodes for energizing the anodes in phase opposition, a common cathode grid circuit for said tubes comprising a condenser and a resistor connected in shunt relationship and a source of a unidirectional voltage having amplitude variations in synchronism with the amplitude variations of said alternating potential connected in series with the condenser and resistor and having its negative pole connected to the grids of said tubes, a source of a constant amplitude undirectional voltage for charging the condenser in phase with the variable amplitude voltage to thereby maintain said tubes in a non-conductive condition, means to vary the phase of the variations of said variable amplitude voltage, a switching element to disconnect said constant amplitude voltage source from said condenser to thereby reduce the negative potential applied to said grids and initiate conduction in said tubes at a time determined by the phase of the variations of said variable amplitude voltage, a resistor element interposed between said grids and said variable amplitude voltage source, means to apply a negative potential to said grids and thereby return the tubes to their non-conductive condition after a predetermined time interval comprising a third discharge tube having a cathode connected to an intermediar voltage point of said constant amplitude voltage source, a grid connected to a point of said source at a negative potential relative to said intermediary point and an anode connected to the control grids of said gaseous discharge tubes, a condenser and a resistor connected in shunt relationship between the oathode and grid of said third discharge tube and a relay element responsive to current fiow in said gaseous discharge tubes having a switching element to disconnect the grid of said third discharge tube from said source of constant potential, and means to cyclically operate said first switching element comprising a relay element for actuating said first switching element, a current source for said relay element and a contactor interposed between said relay element and said current source and actuated by said relay element responsive to current flow in said gaseous discharge tubes.

ANTHONY NEMET.

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

UNITED STATES PATENTS Number Name Date 1,985,069 Anshutz Dec. 18, 1934 1,892,017 Stansbury Dec. 27, 1932 2,147,472 Ulrey Feb. 14, 1939 2,279,311 Grose Apr. 14, 1942

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