US2238987A - Electric time delay device - Google Patents

Description

April 22, 1941. F. G. ALBIN 2,238,987

ELECTRIC TIME DELAY DEVICE Filed DeC. 29, 1938 Patented Apr. 22, 1941 -UNITED STATES PATENT OFFICE :,zsass'l 'morale 'rms DELAY DEVICE Frederick G. Albin, Los Angeles County, Calif., assigner to lloliytech Incorporated, Los Angeles,

Calif., a corporation of California Application December 29, 1938, No. 248,264

13 Claims. (Cl. 175-320) This invention relates to a time delay apparatus and relates more particularly to an electric time delay circuit or device. A general object of this invention is to provide a simple, inexpensive and dependable electric time delay device. l

Time delay devices vare employed where a unit or apparatus'is to'perform a given function for a `given period. Flor example, in making photographic and X-ray exposures, the exposure time is often controlled by a time delay device. Various electrical time controls and time delay devices have been proposed but such devices are usually complicated and expensive. For example, they often contain rectiilers and a plurality of electron discharge devices or electric valves.

Another object of this invention is to provide a time delay device that is extremely simple, embodying only a single electric valve or electron discharge device, the single valve or discharge device operating both as circuit controller and a rectiiler thus distinguishing the invention over prior time delay devices which require separate rectiers.

Another object of this invention is to provide an electric time delay device that is regulable or variable to provide for the control or closing of the controlled circuit for a wide range of selected time periods.

Another object of this invention is to provide a time delay device that is aiected to a minimum extent by variations in the frequency and potential oi the power supply.

Another object of this invention is to provide an electric time delay circuit or device that embodies a manual control whereby the selected or given operating period may be terminated at any time at the will of the operator.

application of the invention, throughout which description reference is made to the accompanying drawing.

The drawing is a wiring diagram of the .improved electric time delay device-of the invention.

The improved time delay circuit. or device of the present invention may be said to comprise, generally, a relay Il for 'governing the circuit II to be controlled, an electric valve I2, two related circuits connected with the valve I2, one an energizing circuit I2 for the relay I0 and the other a control circuit Il governing the energizingcircuit I3, a manual starting switch I5 connected in the control circuit I4 and an auxiliary Another object of this invention is to provide an electric time delay device of the character Just referred to in which the manual control may be manipulated to hold the controlled circuit closed as long as the operator desires, or to interrupt the timing period before its expiration.

A further object of this invention is to provide a time delay device of the character mentioned in which the operation of the means for closing or governing the controlled circuit is accompanied by disconnection of the manual starting switch so that the automatic time delay means is unaffected by continued or successive operations of the starting switch during the selected time delay period. Y.

The various objects and features of my invention will be fully understood from the following detailed descriptionofatypicalpreferred form and switch I6 connected in the control circuit operable to de-energize the relay I0 and operable to energize the relay I0 at the will oi the operator.

The relay It is provided to control or complete the outside circuit or the controlled circuit II In accordance with the invention the relay I Il may be connected in one line II of a suitable A. C. power supply of, say, 110 v., in which case the controlled circuit II is a continuation of the supply circuit or power supply. The relay I0 may include a movable contact element I8 and a stationary contact I9 engageable by the element Il. A lead 20 extends from the power supply line I1 to the contact element I8 and a similar lead 2l connects the stationary contact I9 with the corresponding lead of the controlled circui' I I. The contact element I8 is normally held out oi engagement with the contact I9 by spring means or by gravity. In the preferred form oi the invention a manually adjustable spring ymeans I8a holds the contact element in its normal position. By adjusting the means I8a the time delay period of operation of the device may be varied as will be apparent. ,The relay III further lncludes a winding or coil 22 for operating the contact element I8. 'I'he coil 22 is connected in the circuit I3, as will be hereinafter described,

' and is operable when energized to move the eleindirectly heated.

ment I8 into cooperation with the contact I8 to complete the controlled circuit II.

The electric valve I2 is in the nature of a vacuum or gaseous electron discharge tube. In the preferred arrangement illustrated the valve I2 includes a cathode 23, an anode 24, and a grid of control element 25 spaced between the cathode and anode. The cathode 23 may be directly or In the case illustrated the cathode 23 is of the lament type and is directly heated having leads 28 and 21 extending to power supply means. as will be later described.

The circuit I3 is provided to control or en- Y er'gize the relay I0. The relay energizing circuit I3 includes a lead 28 extending from the plate or anode 24 to the coil 22 of the relay I0. A suitable condenser 29 is preferably connected in parallel with the coil 22 to eliminate undesirable ripples or pulsations.v The circuit I3 further includes a lead 30 extending from the winding or coil 22 to a power supply connected with the cathode lead 26. This power supply includes a power lead 3I extending from a, line I1a of the A. C. power source and connected with the lead 30. A resistance *32 in the form of a lamp is connected across the cathode lead 26 and the lead 3l. The lamp 32 is preferably a carbon lament lamp to counteract or compensatefor variations in the power potential by reason of its resistance characteristics. The potential drop across the terminals of resistance 32 as the result of the current flowing through it is the power supply for the circuit I3. A condenser 33 is connected between the leads 26 and 3l in parallel relation to the resistance 32 to give the potential applied to the circuit I3 the desired phase relation with respect to the phase of the potential of the power supply to circuit I4 as will be later described. 'I'he condenser 33 in addition to the functions to be later described, is related to the condenser 29 to minimize changes in the anodeA current due to changes in the power supply frequency.

The circuit I4 is the control circuit and is connected with the grid or control element 25 of the valve I2 to govern the circuit i3 through the medium of the valve. The circuit i4 includes a lead 34 extending from the control element 25 to a power supply associated with the cathode lead 21. This power supply includes a lead 35 extending from the power supply line I1 and connected with the lead 34. A resistance 3B is connected between the leads 21 and 34 and a condenser 31 is connected in parallel with the resistance 36. The potential drop across the terminals of resistance 36 is the power supply for the circuit I4. condenser 31 affects the phase relation of the potential applied to the circuit i4 with respect to the phase of the potential o the power supply line I1--i1a to give the circuit i4 the correct phase relation. It will be observed that the resistances 32 and 36 are connected in series in the cathode leads 26 and 2i. The cathode or iilament 23 is heated by the current from the power supply leads I1 and I1@- iowing through resistance 36 or condenser 31 or both, and resistance 32 or condenser 33, or both. It will be observed that the condensers 33 and 31 installed as described, permit the employment of resistances 32 and 36 of a higher value so that the current flow is to a large extent through the condensers 33 and 31 and there is a minimum heat loss in the resistances.

The control circuit I4 includes a time control element in the form of a condenser 38. The condenser 38 may or may not be a variable condenser. The condenser 38 is adapted to build up a charge or potential equal to the potential of the power supply for the circuit I4. The control circuit I4 further includes a xed resistance 39 and a variable resistance 40. The resistances 39 and 4I) are connected in series in the lead 34. Either the variable resistance 40 or the condenser 38 may be the time period control means, that is, either one or both of these elements may be manually adjusted to vary the period during which the controlled circuit I I is completed at a given operation of the device. It will be seen that the control circuit I4 associated with the element 25 of the variable resistance 4I! for changing the setting or timing of the device.

The starting switch I5 is adapted to be closed or actuated by the operator to initiate the operation of the device. In accordance with the invention the switch I5 is associated with the circuit I4 and is operable to short out or cause a rapid discharge of the condenser 38. The switch I5 may be varied to suit different uses and installations of the device. drawing, the switch I5 includes a stationary contact 4I connected in the lead 34 and a movable contact 42 operated by a key 43. A lead 44 extends from the movable contact 42 to a. stationary contact at the relay I0. The contact 45 is normally engaged by the movable element I8 of the relay Il). When the key 43 of the switch Il is depressed current flows through the switch I5, the lead 44, the contact 45, the element I8 and the lead 20 connected with the power line I1, thus rapidly discharging the condenser 38. As will be later described, the discharge of the condenser 38 is accompanied by actuation of the relay I0 so that the element I8 is disengaged from the contact 45 immediately following closing of the switch I5. Accordingly, the maintenance of the switch I5 in a closed condition or the repeated closing of the switch I5 while the relay III is energized, has no eiect on the circuits I3 and I4.

The switch I8 is manually operable to cause deenergization of the relay I8 when the latter is energized by reason of the action of the time delay means, and is operable to maintain the relay I0 energized at any time and for any period,

so long as the operator holds the switch closed.

The switch I6 includes a movable contact 48 and The,

valve I2 embodies the timing condenser38 and the 75 a stationary contact 41, both connected in the lead 34 between the condenser 38 and the resistance 39 and 40. The movable contact 48 normally engages the stationary contact 41 to complete the circuit through the lead 34. The switch I6 further includes a second movable contact 48 connected with a tap lead 49. The lead 49 is connected with the lead 34 at a point between the r valve I2 and the pair of resistances 39 and 40.

A manually operable key 50 is provided to depress the contact 48. When the contact 48 is dei pressed to its rst position in cooperation with the contact 46 the resistances 39 and 40 are shunted out. The consequences are that a high potential is impressed on the control element 25, producing de-energization of the relay I0. An understanding of this depends upon a full understanding of the timing operation, to be later described. The timing period is determined principally by the magnitudes of the condenser 38and the total of resistances 39 and 40. Shunting out resistances 39 and 40 by operation of the key 50 effectively reduces the timing period to a very short one, resulting in practically instantaneous de-energization of relay I0.

The switch I6 further includes a contact 52 connected to the resistance 36 by a lead 5I. The contact 52 is engageable by the movable contact 48 when the switch I6 is moved to its second position. When the movable contact 48 is depressed sufficiently to bring the movable contact 46 into engagement with the contact 52 the condenser 38 and the resistances 39 and 40 of the circuit I4 are shunted out to reduce the potential on the element 25 and causes an increase in the potential in the circuit I3 which increased potential in the circuit I3 operates the relay III. As will be understood from a later explanation, the potential applied to the element 25 is greater than the poten- As illustrated in the This minimum normal potential of tial o! the power supply by the potential of the .charge in the condenser 3l. Thus, when the con-` denser 33 is removed from the circuit tosether with the resistances 38 and 43 by a i'ull operation of the switch I8, the potential on the element 2l is reduced. It will be seen that the switch I3 may be manually operated to the iirst position Iollowing the actuation oi the switch I8 to de-energize the relay Ill and thus terminate the time control period, and may be manually held in a fully closed position or second position to hold the relay I8 actuated so that the controlled circuit II may be completed at any time for as long as desired.

The phase relation of the potential impressed on the circuit I4 is opposite to that imposed on the circuit I3 by its power supply. During the half cycles when the potential in the circuit I4 is positive with respect to the cathode 23 current iiows through the control circuit I4 and its condenser 38 and resistances 38 and 40. These halfcycles may be termed the negative half-cycles. The rate of this current is determined -by the potential of the power supply to circuit I4, the potential of the charge in condenser 38, the aggregate resistance of resistances 38 and 43 and the resistance of the interelectrode space between the cathode 23 and the control element 25. Also ail'ecting this current is the electrostatic induction into the element 25 by the other elements such as 24. Disregarding the inductive action, and assuming no discharging circuit for the potential in the condenser 38, after successive negative half cycles, the ultimate potential of the charge in the condenser 38 (when fully charged) equals the peak negative potential oi the power supply for the circuit I4. At any time the potential applied to the circuit I4 is the vector sum of the potentials of the charge in condenser 38 and the power supply of circuit I4. For a fully charged condenser 38, the vector sum ranges from zero to twice the peak potential of the power supply of circuit I4, with an average value equal to the condenser charge. Obviously, with a discharged condenser, the vector sum is only the I potential of the power supply of circuit I4 alone, with values ranging from the negative to positive peak potentials of the power supplyl and an average of zero.

The potential applied to the element 25 with respect to the cathode 23 is approximately equal to the vector sum of the charge potential of the condenser 38 and the power supply for the circuit I4 only when the sum indicates by the direction of the vector that the control element 25 is negative with respect to the cathode 23, from which no current ows and there is no drop in the potential in resistances 38 and 40. Current of thisl polarity or direction cannot flow, and there is no discharge circuit for the condenser 38, as was assumed above, by virtue of the nature oi' the valve I2. No current ows through the relay circuit I3 during the said negative half-cycles because the potential on the anode 24 is negative relative to the cathode 23. Current ows through the relay circuit I3 during the positive half-cycles with a magnitude determined by the value of its power supply, the value of the space impedance in the valve I2, and the general circuit resistance including the relay coil 22, etc. It will be seen that when the potential of the charge in the condenser 38 reaches a maximum the potential on the control element 25 is maximum and negative relative to the cathode 23 so that the anode current and the current in the circuit I3 is at a the circuit I3 is insunicientA to operate the relay Il and the relay is normally dropped or open, as illustrated. The impedance of the anode space in the valve I2 is determined by the normal potential on the control element 28.

To operate the device to complete Kthe outside or controlled circuit II for a given selected time the operator closes the `switch I8. Itis to be understood that the variable resistance 48 may be set to provide for the completion of the controlled circuit I I for any selected period. Closing of the switch I8 causes the condenser 38 to rapid ly discharge, there being a current ilow through the switch I5, the lead 44, the element I8 and the lead 28. The negative potential impressed on the element 25 of the valve I2 during the positive half cycles is thus reduced allowing the potential in the anode circuit I3 to rise to a high value. This sudden increase in the potential in the circuit I3 operates the relay I0 and the relay in turn completes the controlled circuit II. Simultaneously with the operation of the relay I0 the element I8 moves out of engagement with the Contact. to

. remove the short circuit from the condenser 38 so that the condenser 38 may begin to recharge. The time required for the condenser 38 to regain its normal maximum charge is determined principally by the size of the condenser and the value of the resistances 39 and 40. The other factors determining the time necessary for the condenser 38 to recharge are the potential of the power supply for the circuit I4 and the impedance of the valve circuit between the cathode 23 and the control element 25. vThe relay I0 remains operated as the charge gradually builds up in the condenser 38. However, the potential in the relay circuit I3 slowly diminishes as the charge in the condenser 38 increases. When the charge or potential of the condenser 38 reaches a given value the anode current is diminished to a value that allows the relay element I8 to drop'or return by the action of the means Illa to its normal open condition. This, of course, opens the controlled circuit II and terminates the time delay operation of the device.

From the above it will be seen that the selected period of time delay action of the device is determined by the constants of the related circuits I3 and I4 including the resistance 40 and the condenser 38, either one or both of which may be variable to be set to change or vary the time delay period, as desired. It it is desired to open the controlled circuit II before the completion of the selected time delay period of operation of the device the switch I8 is operated to its rst position to short-circuit the resistances 38 and 40 so that the condenser 38 receives its full charge rapidly to effect the restoration of the relay I0. 'I'he manual control switch I6 may be operated to its second position at any time to complete the circuit II and may be held in the second position to keep the circuit II closed as long as desired.

The following is a further explanation of the relationship and action of the elements oi the device. 'I'he condenser 331s connected in multiple with the resistance 32 by connecting one terminal of the condenser 33 to the lead 3| and the other terminal of the condenser to the lead 26. 'I'he phase relation of the potential drop across the resistance 32, which potential is applied to the circuit I3, is shifted with respect to the phase of the A. C. supply potential in accordance with the relative values of the resistance 32 and the condenser 33. The condenser 3l is connected in multiple with the resistance 38 by connecting one of its terminals to the lead 35 and the other to the lead 21. The phase relation of the potential drop across the resistance 36, which potential is' applied to the circuit I4, is shifted with respect to the phase ci' the A. C. supply potential in acvcordance with-the relative values of the resistance 38 and the condenser 31. Thus the relative values of the resistances 32 and 38 and of the condensers 33 and 3l determine the phase relations or the potentials applied to the4 circuits i3 and it.

-Thephase relations of the potentials appearing at the elements 24 and 25 with respect to the cathode 23 of the valve i2, are the results of the phase relations of potentials applied to circuits i3 and M, respectively, together with the eflects oi the circuit elements such as the relay coil 22, the

condenser 29. the resistances 3S and il) and the inter-electrode capacitancesl of the valve i2. .if

the relations of phases appearing at the valve tween the cathode 23 and the control element 25,-

as described above, and therefore, has an effect upon the rate oi charge of the condenser @8.

The condenser 33 has the eflect oi causing the potential in the circuit i3 to lag, thereby delaying the peak negative potential of the element 2li during the negative half cycles when the condenser 38 is receiving its charge. The effect is an acceleration of the charge rate.

Having described only a typical preferred form and application of my` invention, i do not wish to be limited or restricted to the specific details herein set forth, but wish to reserve to myself any variations or modifications that may appear to those skilled in-the art or fall within the scope of the following claims:

Having described my invention, I claim:

1. In an electrical timing device, an electron discharge device having a cathode, an anode and a control element, a source of alternating potential for the cathode, a circuit from said source to the anode, a relay connected in said circuit to .t

be controlled by the anode current, a circuit from said source to the control element, means associated with Athe power source and aiecting the phase relation oi the potentials applied to said circuits so that the potentials imposed on the ani charging relation so that the relay may remain operated for the period required for the condenser to build up its normal charge.

2. In an electrical timing device, an electron discharge device having a cathode, an anode and a control element, a source of A. C. potential for the said discharge device, a relay connected in the anode circuit to be controlled by the anode current, a control circuit from the control element, means for shifting the phase relation of the po- The space tential of one oi said circuits relative to the phase vof the A. C. supply potential so that the potentials imposed on the anode and control element are in opposite phase relations with respect to the cathode during at least a part of the cycle, a condenser in the control circuit adapted to build "up sufilcient potential in the control circuit and control element to normally maintain the potential in the anode circuit so low that the relay is idle, a lead for shorting out the condenser, a switch ior momentarily closing the circuit through said lead to discharge the condenser, and means operated by the relay for opening the circuit through said lead whereby the relay may be operated for the period required for the condenser to build up its normal charge whereby the switch is ineffective while the relay is operative.

3. .An electrical time delay device comprising an electron discharge device having a cathode, an

anode and a control electrode, an alternating current -power source for the cathode, a circuit from the anode, a control circuit from the control electrode, a relay operable by the anode circuit,

, means for supplying the control Aelectrode and the anode with alternating potentials in such a manner that the phase relations of the control electrode and the anode are opposite with respect to the cathode during at least a portion of the cycle. a condenser in the control circuit adapted to normally have a charge of such potential that the potential in the'anode circuit is insufficient to operate the relay, means for momentarily discharging the condenser to cause operation of the relay, and means operated by the relay reestablishing the condenser in its charging relation so that the relay is operated for the period required for the condenser tov-regain its normal charge.

c. An electrical time delay device comprising an electron discharge device having a cathode, an anode and a control electrode, an A. C. power source for the cathode, a circuit from the anode, a control circuit from the control electrode, a relay operable by the anode circuit, means associating the anode circuit and the control circuit wit-h the power source so that thecontrol electrode and' the anode are supplied with alternating potentials of opposite phase relations with respect to the cathode during at least a portion of the cycle, a condenser in the control circuit normally having a charge of such potentialthat the potential in the anode circuit is insufilcient to operate the relay, a-variable resistance in the control circuit, manually operated means for momentarily discharging the condenser to cause operation of the relay, and means operated by the relay reestablishing the condenser in its charging relation so that the period of operation of the relay is determined by the period required for the condenser to regain its normal charge.

5. An electrical time delay. device comprising an electron discharge device having a cathode, an anode and a control electrode, an alternating current power source, a heating circuit from said source for the cathode, a circuit from the anode, a control circuit from the control electrode, a relay operable by the anode circuit, means associating the anode circuit and the control circuit with the power source so that the control electrode and the anode are supplied with alternating potentials of opposite phase relations relative to the cathode during at least a portion of the cycle, said means including sets of multiple related condensers and resistances connected in series in the power source'between the terminals of the cathode and the points oi.' connection of the said circuits with the opposite sides of the power source, acondenser in the control circuit normally having a charge ofl such potential that the potential in the anode circuit is insumcient to operate the relay, means for momentarily discharging the condenser to cause operation ci' the relay, and means operated upon actuation of the relay reestablishing the condenser in its charging relation in the control circuit so that the relay may remain operated i'or the period required for the condenser to regain its normal charge.

6. An electrical time Adelay device comprising an electron discharge device having a cathode, an anode and a control electrode, an alternating current power source for the cathode, a circuit from the anode, a control circuit from the control electrode, a relay operable by the anode circuit, means associating the anode circuit and the control circuit with the power source so that the control electrode and the anode are supplied with alternating potentials of opposite phase relations with respect to the cathode during a portion of the cycle, a condenser in the control circuit adapted to normally have a charge of such potential that the potential in the anode circuit is insufficient to operate the relay, switch means for momentarily discharging the condenser to allow the relay to be operated, switch means operated by the relay reestablishing the condenser in its charging relation in the control circuit so that the relay remains operated for the period required for the condenser to regain its normal charge, and a resistance in the control circuit variable to change the time required for the condenser to build up its normal charge.

7. An electrical time delay device comprising an electron discharge device having a cathode, an anode and a control electrode, an alternating current power source i'or the cathode, -a circuit from the anode, a control circuit from the control electrode, a relay operable by the anode circuit, means associating the anode circuit and the control circuit with the power source so that the control electrode and the anode are supplied with alternating potentials of opposite phase relations with respect to the cathode during a portion 'of the cycle, a condenser in the control circuit adapted to normally have a charge of such potential that the potential in the anode circuit is insumcient to operate the relay, means for momentarily discharging the condenser 'to allow the relay to be operated, switch means operated by the relay reestablishing the condenser in its charging relation in the control circuit so that the relay remains operated for the period required for the condenser to regain its normal charge, aresistance in the control circuit variable to change the time required for the condenser to build up its normal charge, and means for shunting out the resistance to rapidly recharge the condenser to restore the relay.

8. In an electrical timing device, an electronv discharge device having a cathode, an anode and a control element, a source of A. C. potential' for the discharge device. a circuit from said source to the anode, a relay connected in said circuit to be controlled by the anode current, a circuit from said source to the control element, means .tor shifting the phase relation o! the potential of one of said circuits relative to the phase of the potential ot the power source sc that the potentials imposed on the anode and control element are in opposite phase relations with respect to the cathode during a portion of the cycle, a condenser in the last named circuit adapted to build up sufncient potential in the said last named circuit and control element to normally maintain the potential in the nrst named circuit so low that the relay is idle, means for adjusting the relay to change the potential required to maintain the relay in the operated condition, means for momentarily discharging the condenser so that the relay is operated, and means operated by the relay reestablishing the condenser in its charging relation so that the operating period oi' the relay is determined by the period required for the condenser to build up its normal charge.

9. An electrical time delay device comprising an electron discharge device having a cathode, an anode and a control electrode, an alternating current power source for the cathode. a circuit from the anode, a control circuit from the control electrode, a relay operable by the anode circuit, means associating the anode circuit and the control circuit with the power source so that the control electrode and the anode are supplied with alternating potentials of opposite phase relations with respect to the cathode during at least a portion of the cycle, said means including a carbon filament resistance element in the anode circuit to compensate for variations in the voltage of said source, a condenser in the control circuit adapted to normally have a charge of such potential that the potential in the anode circuit is insufficient to operate the relay, means for snorting the condenser to cause operation of the relay by the anode circuit, and means operated by the relay reestablishing the condenser in its charging relation in the control circuit so that the time period the relay may remain operated is determined by the period required for the condenser to retain its normal charge.

10. An electrical time delay device comprising an electron discharge device having a cathode, an

anode and a control electrode, an alternating current power source for the cathode, a circuit from the anode, a control circuit from the control electrode, a relay operable by the anode circuit, means associating the anode circuit and the control circuit with the power source so that the control is insumcient to operate the relay, means for discharging the last named condenser to cause operation of the relay by the anode circuit, and means operated by the relay reestablishing the condenser in its charging relation in the control circuit so that the time period the relay may remain operated is determined by the period required tor the said last named condenser to regain its normal charge.

11. In a device o! the character described, an electron discharge device having a cathode, an anode and a control element between the cathode and anode, a source of A. C. potential for the said device, a relay operated by the anode circuit, a condenser in the circuit ot said control element, means for shifting the, phase relation o! the alternating potential oi' one of said circuits with respect to the alternating potential of the other oi' said circuits so that the potentials imposed on the anode and control element areoppositeintheir Phase relations with respect to the cathode durlng a part of the cycle whereby the potential oi the charge in the condenser and the potential of the control circuit are normally sufcient to maintain the potential in the anode circuit at a low value .where the relay is idle, means tor discharging the condenser so that the relay is opera ated by the anode circuit potential, and means means for shifting the phase relation of the alternating potential of one o said circuits with respect to the alternating potential or the other of said circuits so that the potentials vimposed on the anode and control element are opposite in their phase relations with respect to the cathode during a part of the cycle whereby the poten tial of the charge in the condenser and the poterla tial of the control circuit are normally cumulent to maintain the potential in the anode circuit at a low value where the relay is idle, said means including a condense-:r` and resistance oi related values connected in multiple in one oi said cir cults, means for discharging the forst mentioned condenser so that the relay is operated lor' the anode current, and means operated loy the relay; reestablishiusr the said first mentioned condenser asados? in its charging condition so that the period which the relay remains operated is dependent upon the period required to recharge the said irst mentioned condei'lsers i3. in .a device of the character described, an electron discharge device having a cathode, an anode and a control element between the cathode and anode, a source of il.. C. potential for the said device, a relay operated by the anode circuit, a condenser in tire circuit of said ontrol element, means for shifting the phase relation ci' the altermating potential or one of said circuits with r speci; to the alternating potential of the other oi' vsaid circuits so that the potentials imposed on the anode and control element are opposite in their phase relations with respect to the cathode during c part or the cycle whereby the potential oi' the charge in the condenser and the potential or the control circuit are normally suilcient to maintain the potential in the' anode circuit at a low value where the relay is idle, said means including resistances connected in series with said` l

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