US2564500A - Electronic control apparatus - Google Patents

Description

Aug. 14, 1951 L. c. POOLE ELECTRONIC CONTROL APPARATUS 2 Sheets-Sheet 1 Filed Dec. 29, 1949 INVENTOR. Z/ay/C Ea/e. BY

Aug. 14, 1951 POOLE 2,564,500

ELECTRONIC CONTROL APPARATUS Filed Dec. 29, 1949 2 Sheets-Sheet 2 INVEN TOR.

[034 C FaaZe, BY

Patented Aug. 14, 1951 2,564,500 ELECTRONIC CONTROL APPARATUS Lloyd 0. Fable, Ferndalc, Mich., assignor to Weltronic Company, Detroit, Mich., a corporation-of Michigan Application December 29, 1949, Serial No. 135,789

24 Claims.

This invention-relates generally to electrical timing systems and is'particularly adapted among other uses as a timing system for welding apparatus.

An object of this invention is to provide an improved timer of the character described.

Another object of this invention is to provide such a timing means which uses a minimum number of electric valves.-

Another'object of this invention is to provide such a timing means which is easily and economically manufactured. I

A further object is to provide a novel system for controlling apair of reversedly arranged valves. g v

A further object is to provide in such a systemm eans to insure that one of the valves will always become conductive at a fixed portion of an alternating current voltage wave.

A further object is to provide in such a system such valves'in leading and trailing relation.

A still further object is to provide a control for an electric valve which normally maintains such valve nonconductive but controllable to render such valve conductive.

A still further object is to provide such a control which is actuated by a pair of reversedly arranged valves.-

Another object isto provide a new timing control system for an-electric valve;

Other-objects of this invention will be apparent from the specification; the appended claims and the drawings in which:

Figure 1 illustrates schematically a timing apparatus embodying the invention;

Figs. 2, 3 and 4 illustrate diagrammatically certain control'relations for the controlled valves; and,

Fig. 5 is a modified form of a charging circuit for a'timing condenser used in the apparatus of Fig. 1.

Generically the invention comprises an apparatus for energizing an electrical circuit for a predetermined timed interval and in predetermined relation with'respect to an alternating potential in response to closure of an initiation switch.

Referring to the drawings, an alternating current potential, from a suitable source, is supplied to the lines L5 and L6 through the line switches LS5 and LS'G respectively. A transformer T3 having a plurality of secondary windings 4, 6 and 8 has its primary winding directly connected across the lines L5 and L5. The winding 4 is connected across a time delay relay TDl having normally open contacts TDla which close a predetermined timed interval subsequent to the energization of transformer T3. The winding 6 is connected between the lines L2 and L3 and supplies a control potential for controlling the time winding is is connected through variable resistors R9 and RA 8 and capacitors C4 and C5 to theline L2. This arrangement establishes I a potential between the lines LI and L2 which. is greater than the potential between the lines L2 and L3. .Preferably the windings II and I2 have equal numbers of turns whereby the potential between lines LI and L2 is twice that of the. potential between lines L3 and L2.

The anode of the valve VI is connected to the line LI through the capacitor C3 and a current limiting resistor RI I, as well as .being connected to the line L! through the discharge resistor RI.

The shield grid of the valve Vl is connected to the line Ll through a current limiting resistor m2 and to the cathode of the valve VI through a capacitor C3. The cathode of the valve VI is directly connected to the line, Ll! by means of conductor E8. The control grid of the valve VI is connected to the cathode of the valve VI through a capacitor Cl and through series-arranged resistors Rl3, R5 and RIF: to the movable tap 20 of the potentiometer resistor R8. Capacitors Cl and C2 are arranged in parallel with each other and in parallel with the resistor R5. The common terminal 22 between the resistors R5 and R is connected through the normallyclosed contacts CRla of'relay CRI' to terminal 24 which ismaintained'at the potential of line Ll by its connection thereto through; the conductor 26. The terminal 24 is connected through theprimary winding of transformer T5 to the line L2,the reby placing this primary winding in "parallelwith the series connected resistors R6 and RT and poten- 'tiome'ter resistor R8.

The valves V2 and V3 are connected' in anti- 'parallel relation whereby the'cathode of valve the valve V3 is connected through series connected resistors R2, R3 and R4 to the line L2. The control grid of the valve V2 is connected through a resistor RIG to one terminal of one of the secondary windings 28 of the transformer T5. The other terminal of this winding 28 is connected through resistor R" to the common connection between the capacitor C3 and the anode of the valve VI. Since the cathode of valve V2 is connected to the line LI, it will be apparent that the potential appearing across the capacitor C3 and resistor RI I will appear as a control potential between the control grid and cathodeof the valve V2.

The control grid of the valve V3 is connected through resistor RIB to one terminal of-a second secondary winding 30 of the transformer T; the other terminal of which is connected through resistors RI H and R2 to the cathode of the v'alve V3 whereby the" secondary winding 30 is operable to apply a control'potential'between the control grid and cathode of the valve V3. A capacitor C I 2is arranged in parallel relation with the series connected resistors R19 and R2 to provide a phase shift for the valve V3 control potential which will lag the voltage applied across the anode and cathode of the valve V2. p This voltage across 012 due to the conduction of valve V2 will be a polarity to render valve V3 conductive and is of sufiicient magnitude relative to the blockin volta e applied by windingilo to render valve V3 conductive so that when the valve V2 h'as'conducted during one half cycle of applied I voltag'ethe' valve V3 will be rendered conductive during the following half cycle of opposite polarity of said voltage.

"The. windings I4 and II are preferably of an equal number of turns and arranged in polarity to provide, in effect a single center tapped winding having the free end of the winding II connected through capacitors C4 and C5, terminal 3| and resistors R9 andBlfl to the free end of thelwinding I4. As the relative values of re-.

sistance and capacitance of this just described circuitare varied, the phase relation of the voltage appearing between terminal 3! and line L3 will vary with respect to that of the voltage be.- tween the free terminals of the windings II and 44. Since the phase of the voltage appearing between the lines L5 and L6 bears a definite relationto that of the last mentioned voltage, this phase shiftable voltage, appearing between. the line L3,.and terminal 3! is utilized to supply a control volta e forrtlievalves V4 and V5 which in the present instance is used to render these valves conductive. A transformer T6 therefore has its primary winding connected between the line. L3..and,.the terminal 3! and is provided with a pair of secondary windings 32 and 34 which respectivelyapply a blocking bias potential between the control grid and cathode of the valves V4 and V5 respectively. One terminal of the secondary winding 32 is connected through the secondary winding of the transformer TI to terminal 3B which terminal 36 is directly connected to the cathode of the valve V4. The other terminalof thewinding 32 is connected to terminal 38, and thecontrolgrid of the valve V4 through the resistor R20 and rectifier 40. A resistor R2I is connected across the winding 32 and rectifier 40 to provide for current flow through the rectifier 40 whereby it is effective to prevent the winding 32.from providing any substantial positive grid to cathode potential. A stabilizing con denser C8 is connected between the terminals 35 and 38.

The valves V4 and V5 are normally provided with a hold-off voltage from the transformers TI and T2 respectively. The secondary winding of the transformer TI is connected between terminaltfiand the common terminal of the resistor R2I and winding 32 whereby it is effective to provide an alternating current bias voltage across the capacitor C8 and consequently the gridand cathode of valve V4. The voltage for energizingthe transformers TI and T2 is derived between the common terminal 2 of resistors R3 and'R l and the common terminal I3 between the windings II and I2 as represented by the 1ine L3.. Normallythere is a difference in potential between the terminals 2 and IS with the valves V2 and V3 nonconductive. However upon conduction of the valves V2 and V3 this potential difference disappears-since the resistance of the resistors R4 and the sum of the resistance of resistors R2 and R3 plus the effective resistance of the valves V2 and V3 is matched with the voltageacross the windings I I and I3 respectively. It is believed that the remainderof the construction can best be understood by a description of the'operation which is as follows: a

The circuits are preparedfor operation by closure of the line switches LS5 and LS6 whereby the lines L5 and L6 are supplied with an alternating potential. This closure energizes the transformer T3 whereby winding 4 supplies a potential-for energizing the time delay relay TDi which will close its contacts TDIa at a predetermined subsequent time. Winding 6 energizes the lines ;L2 and LSwhereby the winding l I of transformer T4 is energized as well-as transformer T3. Winding 8 energizes the; filaments of valves VI-V5 inclusive throughsuitable control circuits which may include transformers if desired to maintain the filament to cathode voltage withimpermissible values. rEnergization of winding I I 'causes'transformer Tdgtdprovide a voltage between lines-LI and L2 which is greater than thatbetween lines L3 and L2; If; as is preferred, the windings II and I2 are :similar. the voltage between lines Li' and: L2 will be twice that between lines L3 "and'LZ; Since transformers TI and T2 are connected between terminals 2 and I3 and valves V2 and V3 are normally;nonconductivei or blocked these trans formers will'zbe energizedto place an alternatingvoltage between the grids and cathodes of the valves, V4 an'dJV5 which voltage is phased with respect to the voltage applied to these main electrodes 'so' that a blocking grid-to-cathode bias will be applied during the time that their anodes are positive with respect to their cathodes as is diagrammatically shown in Fig. 4.

Since the relationships are the same for each set of valves V4, V5 and V5, V1 except that they are'180 out of phase with respect to each other, Fig. 4 will explain thevoltage relationships of each 'set of valves and a detailed explanation will be given only as to one set. Ea represents the potential supplied between the anode and cathode of the valve V6 which during periods of nonconduction of valves V6 and V1 will be that appearing across the anodes and cathodes of the valve'V4. Ia represents the normal load current." which will flow through valves VB and Vi during their conduction and is shown in lagging relation to the voltage Ea since this is the nor-- malrelation for the welding application shown. Eb represents the blocking bias voltage applied by the transformer TI which"acts' to malintain and RH? to provide a control voltage Es which may be set to provide for conduction of the valve V l at'the desired point on the voltage wave Ea to provide so called heat control Energization of lines LI and L2 5 also energizes the transformer T5 whereby windings 2B and are energized. Winding 25 is phased to place a firing voltage between the grid and cathode of the valve V2 but is initiallyprevented from doing so by the now open contactsTDIa. A Winding 38 places a blocking bias between the grid and cathode of the valve V3.

Capacitor C3 will be charged by conduction of the normally conductive valve VI fromline LI through current limiting resistor R! I, capacitor C3, anode to cathode of valve VI, and iconductor I8 to line LI which soonreaches a "fully charged condition. Relay CRI is-normally deenerg-ized' whereby its normally closed contacts CR Ia act to complete a charging circuit for the capacitors CI and C2. 7 line L3 through conductor 25, contacts'CRIa, capacitors CI and C2, resistor RI3, grid to cathode of valve V I to line L2.

As soon as the relay TDI times out, it"closes its contacts TDIa whereby the winding 28 is efiective to supply its potential between the grid and cathode of valve V2 inseries with the po tential of the now charged capacitor C3. The values and polarities of these potentials are such that the valve V2 is held blocked.

It is to be assumed that the electrodes have now been clamped against the work by suitable means, not shown; so that they are in condition to be energized to perfecta weld.- Upon closure of the initiation switch SWI, therelay CRI will be energized through an'obvious circuit opening its"contacts CRIa 'de-energizing the charging circuits for the condensers CI and C2 and plac ingthe charge thereacross'between the-grid and cathode of the valve VI to negatively-bias this grid-with respect to the cathode whereby the valve V! is rendered nonconductive permitting the charge on the capacitor C3 to bleed off through the discharge resistor RI which after a predetermined timing allows valve V2 to conductl- Conduction of valve V2 causes valve V3 to conduct in trailing relation with respect to the valve V2 for completing a circuitbetween the lines L! and L2. The values ofresistors R2, R3 and R4 are so chosen that with the valves V2 and V3 conducting the terminal 2 intermediate the resistors RS-and R4 will be rendered at an intermediate potential which is the same potential as line L3 whereby the transformers TI and T2 which normally act to maintain the'valves' V4 and V5 blocked will be de-energized, permitting these valves V4 and V5 to conduct Conduction'of the valves V4 and V5 causes the ignitrons V6 and V1 respectively to conduct whereby current flows between lines L5 and L6 to energize the welding transformer T3 causing current to flow between the electrodes Ethrough the work W. When the charge on the condensers Ci and C2 has discharged through the resistor R5 to a predetermined value, the differential This circuit extends from 7 andresistor RII due to the charging action of bias voltage applied betweenithe grid and cathode of the valve V2.- Curve El 5 represents the voltage 6 voltage set' up-1 through theresistor "R1 and potentiometerresistor- R8 Will again permit the valve VI to: conduct thereby againcharging the capacitonC3 to block-the valvesVZ and V3. The

rehdringbf the valves V2 and V3 nonconductive again -establishes potential difference between the terminal 2 and line' L3 which re-energ-izes thetrahsformers-TI' and -T2 for blocking the valves -V i and V5 thereby terminating current flow through the valves V6 and V1.

In Fig. 3, E I- illustrates the voltage relationship of anode to cathode of the valve V2, E2 the voltage of anode to cathode of V3, E3 the unbloclting voltage established across capacitor CI2 dueto-the conductionof--V 2, and E4 is the blocking voltage of the winding 30 applied to valve V3. Theyoltage E3 is seen to lag the voltage ELdue-to the lagging effector" circuit elements consisting-ofcapacitor'CI2 and RI!) so that when the proper anode to cathode voltage appears acrossthe valve V3 the sum of'the voltages E3 and- EA will produce a "resultant voltage to fire or;reiider valve V3 conductive at substantially the beginning of the voltage pulsejEZ;

In Fig. 2,'there is shown diagrammatically the voltag'ejrelations acting to control the conduction of valve V2 with respectto valve VI so that irrespective of-thetimein the voltage cycle which is applied between the-anode and cathode of "valve "V2 that-the-switch SWI is closed, the

valve V2 will always commence its conduction in predetermined relationship to the voltage apnegative portions having been omitted for clarity. I EI I represents the "positive half cycles of the I its phase relation-with respect toEI 3; thenegaanode to cathodevoltage on the valveVI and tive portions-havingbeen' omitted for clarity. EIZ' represents thevoltage component applied between the grid andca'thode of the valve V2 by the winding zawhich' due tothe phase shift imparted thereto by the capacitor CI3, will lag 'thevoltage'EI I and will therefore tend to permit firing-of the valve V2 only during the first part of'the-positive cycle 'of'thevoltage -EIIl.- EI3 represents the potential-across the-capacitor C3 the valve VI and discharging action of resistor R! during the positive and negative half cycles of voltage EH respectively; EM represents the sum of the voltages BIZ and EI3.or the actual component applied between the grid and cathode oi the valve -VI by the capacitors CI and C2. Curve "EIG represents the alternating current voltage component applied between the grid and cathode of the valveVI due to the voltage drop across the righthand portion of the potentiometer R8 andthe' resistor-R1. Curve EII represents thesum of thevoltages EI5- and EI 6.

The valve VI is-of the type generally sold to 1 the trade under the designation 2050 in which the curve E I 4a.

- transformers 'II former TIA connected in parallel with the transformers-TI and T2. ondary winding 50 of transformer TIA is connected through a rectifier 52 to one terminal of cathode thereof. For reasons to be pointed out hereinafter it may be desirable in many instances to render the capacitor C6 and resistor R2 variable whereby the time in the voltage wave El I at which the valve VI conducts may be controlled. Such an arrangement controls the charging of the capacitors CI, C2 and C3 whereby they may be brought once each cycle of the voltage EII to a fully charged condition. Termination of conduction by the valve VI initiates simultaneously the discharge of the capacitors CI, C2 and C3.

' ,The line tr represents a time subsequent to closure of the line switches LS5 and LS6 and to the closing of contacts TDIa and in which equilibrium conditions of operation have been established. If now the switch SWI is closed during the time interval from tI to 152 the valve V I will fail to fire during the next positive wave of voltage El] and the condenser C3 will disto cathode voltage on valve V2 represented by The. valve V2 will then be fired at time t3. If the switch SWI is;closed :during the interval between t4 and Til, the valve VI having commenced conducting will continue to conduct and recharge the condenser C3 but dueto-opening of the contacts CRIa the charging circuit for the condensers CI and C2 will be opened and their charge would be the charge at the instant the contacts CRIa opened. As indicated above, by phasing the bias voltage between shield grid and cathode of the valve VI so that valve VI is rendered conductive just before the 90 peak of the voltage El I is reached. The time interval in which the switch contacts 'CRIa may open to terminate charging of the condensers CI and C2 and yet permit condenser C3to' charge is so small that an opening of the contacts CRIa during this period is extremely improbable. Under the extreme condition, in

' which contacts CRIa are opened at the exact instant valve VI conducted, the introduced error shown in Fig; 5 may be used wherein the charging circuit for the timing condensers CI and C2 may include'a second secondary winding on one of the or T2 or a separate trans- One terminal of the secthecapacitors CI and C2 while its other terminal is connected to the other terminals of these capacitors. The winding 58 is phased with respect to the voltage between lines L3 and L2 such that a charging voltage of the polarity indicated will be applied to the condensers CI and C2 when line L3 is positive with respect to line L2. In this manner the capacitors will be recharged each cycle of the voltage applied between lines L3 and L2 in which the valves V2 and V3 are not conductive. As indicated in Fig. 2 there will always be a constant number of positive half cycles of the voltage EII between the time valve VI is rendered nonconductive and valve V2 is rendered conductive. .As shown the capacitor C3 and retime the condensers CI 8 sistors RI and RI I provide for one such half cycle. Furthermore the combined effect of capacitor C3 and winding 28 always provides for the valve V2 to be rendered conductive at a fixed point in the voltage wave EIU so that the discharging of the capacitors CI and C2 will always remove the blocking bias voltage on valve VI at a fixed time interval subsequent to firing of the valve V2 for terminating the weld interval. This efiect is independent of the place along the voltage waves at which the switch SWI is actuated.

Subsequent to a predetermined time the condensers CI and C2 will have discharged sufficiently so that the voltage EI'I will become sufiiciently positive, or less negative, so that the valve VI will again be rendered conductive. Conduction of the valve VI will again establish a charge on the condenser C3 which will apply a blocking potential between the grid and cathode of valve V2 whereby it is rendered in a condition to re-establish conduction if it is already nonconductive or if valve V2 is already conducting such charge on the capacitor will prevent its conduction during the next cycle in which its anode is positive with respect to its cathode. The valve V3 which conducts each subsequent half cycle to the half cycle in which valve V2 conducts will cease conducting after the next half cycle in which valve V2 conducts. At this point it is to be noted that the superimposing of the alternating potential E I t on the potential E I 5 acts to provide ,a more definite time for theconduction of valve VI.

When valves V2 and V3 cease conducting the potential of terminal 2 again becomes different from line L3 and the transformers TI and T2 are again energized to impress a blocking voltage on the valves V4 and V5 respectively which overcomes the conducting voltage set up by transformer T5 whereby valves V4 and V5 are rendered ineffective to fire the valves V6 and V1 to terminate the flow of welding current.

'If the switch SWI has been opened during this and C2 will become charged as stated above and the system is in condition for a subsequent operation. If the switch SWI is kept closed, the condensers CI and C2 cannot charge because of the open contacts CRIa and the system will remain in condition to prevent conduction of the valves V6 and VT. The electrodes can now be unclamped from the work.

As shown and described, the switch SWI is manually operated but it is to be distinctly understood that the switch SWI and/or circuit to the relay CRI may be controlled by a suitable sequencing circuit which acts to automatically clamp the electrodes to the work and to close the switch SWI subsequently to the clamping of the electrodes on the work and which will, at the termination of the weld period, open the switch SWI and unclamp the electrodes. If desired the sequencing circuit may include means for delaying the unclamping of the electrodes for a predetermined time interval subsequent to the termination of the flow of welding current and may also include means for insuring against reclosure of switch S-WI and reclamping of the electrodes within a desired time interval.

What is claimed and is desired to be secured by United States Letters Patent is as follows:

1. In a timing apparatus of the character described for controlling the flow of electrical energy from a source to a load, a first valve havingjnain electrodes and a control electrode, a

valve main electrodes and one of said source 'con-' ductors, circuit means connecting said device between one of said second valve main electrodes and said second valve control electrodaa second storage device, and means including switch means for selectively connecting saidsecond device loo-- tween said first valve control electrode andsaid one conductor and between said first valve control electrode and the other of said first valve main electrodes.

r 2. In a timing apparatus of the character described for controlling the flow of electrical energy from a source to a load, a firstvalve having main electrodes and a control electrode, a second valve having main electrodes and a control electrode, said ,m' m electrodes of said valves being arranged in opposite polarity between a pair of conductors adapte'd to be energized from a source of alternating potential, an energy storage device connected intermediate one of said first valve main electrodes and one of said source conductors, circuit means connecting said device between one of said second valve main electrodes and said second valve control electrode, a second storage device, means including switch means for selectively connecting said second device betweensaid first valve'control electrode and said one conductor and between said first valve control electrode and effectively to the other of said first valve main electrodes, and means supplying an alternating potential between said second valve control electrode and said second valve one main electrode.

3. In a timing apparatus, a first transformer having a pair of windings, a first pair of conductors adapted to be energized from a source of alternating electrical potential and connected across a first of said windings, meansconnecting said pair of windings in voltage additive series connection, a second pair of conductors energized by the voltage derived from said series connected windings, a first electric valve having an anode and a cathode and a control electrode, an energy storage device, a first circuit means serially connecting said device ands/said anode and said cathode between said second pair of conductors with said device intermediate said anode and one of said second pair of conductors,

a pair of valves each having an anode and a connected resistor elements connectingthe said cathode of the other of said pair of valves to the other of said second pair of conductors, a second transformer having a pair of windings, a third circuit means connecting one of said 'second transformer windings between a common connection of said serially connected elements and a common connection between said first transformer windings.

i. In an apparatus of the character described,

an electric valve having an anodeand a cathode and a control electrode, a first supply means operable to supply an'alternating potential, a. second supply means 'operableto supply an alternating potential, a rectifier, circuit meansserially connecting said first and said second. means and said rectifier, means connectingsaid circuit means between said c0ntro1 electrode and said cathode, a resistor connected in shunt with one ofsaid supply means and said rectifier and means for controlling the relative phases of the potentials supplied between said control electrode and said cathode by said first and second means.

j 5 111 a timing apparatus, a-first. transformer having a pair of windings, a first pair ofconductors adapted to beenergized from a source of alternating electrical potential and connected across a first of said windings, ..means connecting said pair of windings-in voltage additive series connection, a second pair. of conductors energized by the voltage derivedfrom said se-' ries connected windings, a firstielectricavalve having an anode and a cathode and a control electrode, an energy storage device, a first circuit means serially connecting said deviceand said anode and said cathode between said second pair of conductors with said device-intermediate said anode and one of said second pair of conductors, a pair of valves each having an anode and a cathode and a control electrode, a first conductor means connecting said anodes and said cathodes of said pair of valves in antiparallel relation, one of said pair of valves having its said cathode connected to said one conductor, a second conductor means connecting said control electrode to said first circuit means intermediate said first valve anodeand said storage device, a second circuit means including apair of serially connected resistor elements connecting the said cathode of the other of said pair of valves to the other of said second pair of conductors, a second transformer having a pair of windings, a third circuit means connecting one of said second transformer windings between acomrnon connection of said serially connected resistor elements and a common connection between said first transformer windings, a third winding for said first transformer, means .connecting said first transformer first windingand said third winding in series additive relation to provide a pair of end terminalsrand a centerterminal, a load circuit comprising a resistive and areactive impedance element serially connected together and connected between said end terminals, athird transformer having afirst and second winding, means connecting said third transformer first winding between said load circuit and said center terminal, a second electric valve having an anode and a cathode and a control electrode, circuit means for serially connecting together the other of said pair of windings of said second transformer and saidthird transformer second winding, said last-named. circuit means being connected between said sec-- ond valve control electrode and cathode.

6. The combination of-claim 5 in which a rectifier is serially connected between said third transformer second winding and-said third valve control electrode and in which an impedance element isconnected to said rectifieron the side thereof adjacent saidthird valve control electrode and to the common connection between said third transformer second winding and said second transformer other winding.

'7. In a timing apparatus, a first transformer having a pair of windings, a first pairof conductors adapted'to be energized from a source of alternating electrical potential and connected across a first of said windings, meansconnecting said pair of windings in voltage additive series connection, a second pair of conductors energized by the voltage derived from said series connected windings, a first electric valve having an anode and a cathode and a control electrode, an energy storage device, afirst circuit means serially connecting. said device and said anode and said cathode between said second pair of conductors with said device intermediate said anode and one of .saidsecondpair of conductors, a pair of valves each having an anode and a cathode and a control electrode, a first conductor means connecting saidanodes and said cathodes of said pair of valves in anti-parallel relation, one of said pair of valves having its said cathode connected to said one conductona second conductor means connecting said 7 control electrode to said first circuit means intermediate said first valve anode and said storage device, a second circuit means including a pair'of serially connected resistor elements connecting the said cathode of the other of said pair of valves to the other of said second pair of conductors, a second transformer having a pair of windings, a third circuit means connecting one of said second transformer windings between a common connection of said serially connected elements and a common connection between said first transformer windings, a capacitor connected in parallel circuit with a portion of one of said resistor elements, a third transformer having an output winding connected between said control electrode of the other of said pair of-valves, and serially through said lastnamed capacitor and said resistor element portion to said other valve cathode.

8. In a timing apparatus, three conductors adapted to be supplied with an alternating potential in which the potential between a first of said conductors and a second of said conductors is equal to the potential between said first conductor and a second of said conductors and the potential between said second and said third conductors is the. sum of, said first and said second named potential, switch means, impedance means having end connections and an intermediate connection, circuit means connecting said switch means and said impedance means in series circuit between said. second and said third conductors, and a controlling circuit connected between said intermediate connection and said first conductor.

9. The combination of claim 8 in which said impedance means comprises two portions which have the same ratio as the potential between said first and second conductors and said second and third conductors whereby when energized through said switch means said impedance means acts to establish a potential at said intermediate connection which is equal to the potential of said first conductor whereby to efiectively de-energize said controlling circuit.

10. The combination of claim 8 in which said switch means comprises a pair of anti-parallel connected electric valves.

11. The combination of claim 10 in which one of said valves comprises a main electrode and a control electrode, in which means is provided to establish a control potential between said control electrode and said main electrode, and in which switch means is provided for controlling said potential.

12. The combination of claim 11 in which said 12 establishing means comprises an energy storage device and said last-named switch connects said device between two of said conductors.

13. In a timing apparatus, three conductors operable to be energized from an alternating current source in a manner to provide voltages be-- tween a first of said conductors and each of the other of said conductors and to provide a voltage between said other two conductors which is greater than the voltage between said first conductor and either of said other conductors, a pair of electric valves connected in anti-parallel relation, each of said valves being controllable by a bias potential placed between a control electrode and a main electrode, a plurality of impedance elements, means connecting said main electrode of one of-said'valves to one of said other conductors, means connecting said impedance elements in series circuit between a sec- 0nd of said other conductors and said main electrode of another of said pair of valves, a controlling impedance element and a third electric valve arranged in series circuit between a pair of said conductors, circuit means for placing the potential appearing across said controlling ime pedance element between said main electrode and said control electrode of a first of said pair' of valves, and means controlling conduction of said third valve.

14. The combination of claim 13 inwhicha control circuit is connected between said first conductor and to said series connected elements at a point intermediate a pair of said series connected elements. I

15. The combination of claim 14 in which means is provided to establish a bias potential between said main electrode andsaid control electrode of a second of said pair of valves tending to hold said second valve nonconductive, and means actuated as a consequence of current flow through said first valve for overcoming said lastnamed bias potential whereby said second valve will be rendered conductive as a consequence of the'conductionof said first valve.

16. The combination of claim 15 in which said last-named means comprises a reactive"imped'- ance element connected in parallel relationwith one of said series connected impedance elements and in series circuit with said bias potential establishing means. J

17. In a timing apparatus, a pair of conductors adapted to be energized from a source'lof electrical energy, a first impedance dementia first electric valve having mainelectrodes 'anda control electrode, circuit means connecting said element to one of said pairof conductors and to one of said main electrodes, and connecting fthe other of said main electrodesto' the otherof said pairs of conductors, a second impedance element,

means connecting said second element to said control electrode, means selectively connecting said second element to receive a potential from either of said conductors, a second-electric valve having main electrodes and a control electrode, a third impedance'means, circuit means connecting one of said second valve main electrodes ;to said one conductor and connectingtheother of said second valve main electrodes throughsaid third impedance means to said other conductor, conductor means connecting said second. .valve control electrode to a portionof said first-named circuit means intermediate, said first. valve one main electrode and said first impedance element.

' 18. Thecombination of claiml'? in which said third impedance means is provided with an intermediate top connection, in which is provided a third conductor adapted to be energized from such source at a potential intermediate the potential between said pair of conductors, and in which a control circuit is energized by the potential appearing between said intermediate conmotion and said third conductor.

19'. The combination of claim 18 in which said first and second impedance elements are energy storage devices and said third impedance means is resistive in character.

20. The combination of claim 19 in which an alternating potential supplying means is provided in said last-named conductor means.

21. In a timing apparatus of the character described for controlling the flow of electrical energy from a source to a load, a first valve having main electrodes and a control electrode, a second valve having main electrodes and a control electrode, said main electrodes of said valves being arranged in opposite polarity between a pair of conductors adapted to be energized from a source of alternating potential, an energy storage device connected intermediate one of said first valve main electrodes and one of said source conductors, means providing a controlled rate of discharge for said storage device, circuit means connecting said device between one of said second valve main electrodes and said second valve control electrode, a second storage device, means providing a controlled rate of discharge for said second storage device, and means including switcli means for selectively connecting said second device between said first valve control electrode and said one conductor and between said first valve control electrode and the other of said first valve main electrodes.

22. In a timing apparatus of the character described for controlling the flow of electrical energy from a source to a load, a first valve having main electrodes and a control electrode, a second valve having main electrodes and a control electrode, said main electrodes of said valves being arranged in opposite polarity between a pair of conductors adapted to be energized from a source of alternating potential, an energy storage device connected intermediate one of said first valve main electrodes and one of said source conductors, circuit means connecting said device between one of said second valve main electrodes and said second valve control electrode, a second storage device, means including switch means for selectively connecting said second device between said first valve control electrode and said one conductor and between said first valve control electrode and the other of said first valve main electrodes, and means connected in series with said first-named energy storage device and said second valve control electrode for supplying an alternating potential between said second valve control electrode and said second valve one main electrode.

23. A network for connection between a control electrode and a cathode of an electric valve, a pair of terminals adapted to be connected across such electrode and cathode, a first source of alternating potential adapted to provide an alternating potential bias between said pair of terminals, a second source of alternating potential, and means energized from said second source for applying instantaneous potentials from said second source between said pair of terminals proportional to the instantaneous potential of said second source during corresponding half cycles thereof and to prevent said second source from supplying a potential proportional to the instantaneous potential of said second source during opposite corresponding half cycles thereof.

24. The combination of claim 23 in which means is provided to phase shift the voltage potential applied by said second source.

LLOYD C. POOLE.

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

UNITED STATES PATENTS Number Name Date 2,394,087 Mahoney Feb. 5, 1946 2,441,789 Bivens May 18, 1948 2,482,892 Barwick Sept. 27, 1949

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