US2679598A - X-ray apparatus - Google Patents

Description

May 25, 1954 R. L. WRIGHT ET AL 2,679,598

X-RAY APPARATUS Filed Dec. 4, 1950 2 Sheets-Sheet 1 Electro- Fig.|A.

curdiogruph Camera Conlocfor WITNESSES: INVENTORS c Robert L.Wright, Walter $.Lusby William C.whiflenbgrg g nd williom J.Lee.

' ATTORNEY May 25, 1954 R. L. WRIGHT ET AL 7 2,679,598

X-RAY APPARATUS Filed Dec. 4, 1950 2 Sheets-Sheet 2 Fig.|B.

20 I2 22 Mg 20s;

WITNESSES: INVENTORS b RobertLWright, WolterS.Lus y Wil liom Qwhifienberg and William J. Lee.

Patented May 25, 1954 X-RAY APPARATUS Robert L. Wright, North Linthicum Heights, Walter, S. Lusby, Severna Park, and William J. Lee and William C. Whittenberg, Baltimore, Md., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 4, 1950, Serial No. 198,958

12 Claims.

Our invention relates to X-ray apparatus, and more particularly to X-ray apparatus for use in angiocardiography.

In medical studies of the heart, known as the science of angiocardiography, a material opaque to X-radiation is injected into the veins of a patient and photographs are taken of the patients heart by means of X-rays, as the opaque material passes through the heart. For some purposes, it is desirable that repeated pictures be taken at equal time intervals. For other purposes, it is desirable that repeated pictures be taken with the heart in the same position. For these latter purposes it is desirable that the photographing process begin at the time that the opaque material first enters an auricle of the heart, that it continue during the time that the opaque material is in that auricle, and cease when the opaque material leaves that auricle. While some types of apparatus have been devised whereby pictures are taken in coordination with the heart beats so that successive pictures are taken while the heart is in the same position, there has been no apparatus built, to our knowledge, that will ensure that the X-ray film will be exposed only while the opaque material is in the heart.

It is, therefore, an object of our invention to provide X-ray apparatus for use in angiocardiography wherein the photographic process is so controlled that the taking of pictures will begin as soon as the opaque material enters an auricle of the heart, and stopped as soon as the opaque material leaves that auricle.

It is an ancillary object of our invention to provide a control circuit for an X-ray apparatus whereby exposures may be made at predetermined repetition rates for predetermined intervals of time, which intervals are separated by other predetermined intervals of time.

Another object of our invention is to provide a circuit whereby the output from an electrocardiograph is applied to an X-ray control apparatus at predetermined intervals of time.

An ancillary object of our invention is to provide X-ray apparatus for angiocardiography wherein the apparatus must be manually reset for each successive cycle of operation.

Another object of our invention is to provide X-ray apparatus for use in angiocardiography wherein X-ray exposures are made, responsive to signals from an electrocardiograph; or alternatively signals from a camera; or alternatively signals from a multivibrator.

Still another ancillary object of our invention is to provide testing means for an angiocardiography sequencing timing control circuit wherein the responses of the control circuit may be viewed visually by an operator so that he may check the timing of the circuit prior to operation of the X-ray apparatus.

In accordance with our invention we provide an angiocardiography sequencing apparatus for the control of an X-ray apparatus. Included in this sequencing apparatus are connections for receiving the output from an electrocardiograph; or alternatively, for receiving the output from a camera control circuit in which an electrical pulse is produced each time a film is in place; or alternatively, a multivibrator circuit for producing periodic electrical pulses. Switches are provided for controlling the contactor, which controls the X-ray tube, responsive to the electrocardiograph,

or alternatively to the camera, or alternatively.

to the multivibrator. A timing circuit is provided comprising a plurality of electric discharge devices, such as thyratron tubes, connected so that the first one is triggered by external means and each succeeding tube is rendered c0nductiv e in response to the conduction of the tubes immediately preceding. A time delay is provided between the conduction of each thyratron tube and conduction of the immediately succeeding thyratron tube. The thyratron tubes are connected to a plurality of respective switching means, whereby their outputs cause the operation of the respective switching means. These switching means control the contactor which in turn controls the firing of the X-ray tube.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood when read in connection with the accompanying drawings, in which the Figures 1A and 1B constitute a schematic showing of an apparatus embodying our invention.

Referring now to Fig. 1A, we provide an X-ray tube 2 connected to the secondary winding of a transformer 6. The primary winding of the transformer 6 is connected through a contactor 8 to a suitable source of alternating current, not shown.

A pulse generator selector switch It] is connected electrically to an electrocardiograph l3, a camera It, and by means of mechanical and electrical connections, to a multivibrator I6, Connected mechanically to the pulse generator 3 selector switch I is a camera switch II for providing a different connection to the camera I4 when the original pulse is received from the camera I4 than when the original pulse is received from the electrocardiograph I3 or the multivibrator I6.

Connected in series with the switch I0 are a plurality of relay actuated switches for determining the periods during which the pulses produced by either the electrocardiograph I3, the camera I4, or the multivibrator I6 are allowedto reach the contactor 8 which controls the X-ray tube 2. These latter relay actuated switches are operated by a series of time delaycircuits, with which are associated a plurality of electric discharge devices, such as thyratrons.

A first control thyratrontube '28 is provided with a control grid 29 connected through apparatus 30 to ground at 3|. This apparatus 30 may be a s witch which the physician pushes at the timerthat he injects the opaque material into the blood of the patient, or maybe 'a connection of the syringe which will ground that grid to the patient when thesyringe discharges the opaque material into the patients veins. When the grid 29 grounded, the negative bias which is normally impressed thereon is removed and the first control thyratron 28 is immediately rendered conductive. This starts the operation of the timing cycle.

Connected to the anode circuit of the first thyratron v"P8 is a relay 32 which operates 2. normally closed switch 34. When the tube 22 conducts, the switch 34 is opened, disconnecting the negative bias supply from the grid 36. After a predetermined time the negative bias on grid 36 leaks off so as to :render the second thyratron 38 conductive. Connected to the outputof the sec- 0nd thyratron 38 is a relay which operates three switches, I2, 46 and-42. When the second thyratron 38 conducts andcauses the switch 42 to open,

the negative bias supply isremoved from the .control grid 44 of the third thyratron 46,.and the negative bias islallowed to leak-off, thereby allowing the. tube 46 \to conduct. Thisprocess continues through .thefourth and. fifth control thyratron tubes 48and'50.

Connected .to. .thegrid of eachof-the control .thyratrons.38,46, 48, .5Il,.is.a condenser I53, I55,

.I.5'I,.1I6I,.and.a variableresistance I63, I65, I61, I69. The resistor I.63,.I65, I61, I69 andthecondenser. r53, l I 55, J I 51, I-BI areconnected .to the control grids of thezcontrol'thyratrons:38, 46,48, 50

to: provide artime delaygcircuit so that substantial -time.is required-for thenegative bias on the .con-

trolgrid-of the respective thyratron tube to leak .off. .Since the resistances I63, I65, I61, 169 are variable, the period of time between the time of firing of each tube and the time of firing of the succeeding tube, may beadjusted. Thus, when the opaque material is first injected into the patients body, asubstantial time delay is provided before the secondcontrol thyratron tube 38 con- .ducts and causes operation of the switch I2. If

the time when the opaque material leaves the right auricle, and the time it enters the left auricle after traversing the lungs. The period of time between the firing of the fourth control thyratron 48 and the firing of the fifth control thyratron 50 is equal to the'length of time during which the opaque material is passing through the left auricle.

Thus, when the second thyratron 38 fires, it operates a relay in its output circuit, closing the switch I2 in the contactor control circuit. This allows'theX-ray control contactor to operate and cause the X-ray tube to conduct. The operation of the contactor 8 will continue in response to electric pulses from the electrocardiograpli it, or alternatively the camera I4 or alternatively the mu'ltivibrator I6, until the third thyratron 66 fires. When the third thyratron fires it operates a relay 56 which opens=the switch 20 in the con- .trol circuit of the contactor 8. Thus, when the third thyratron 46 fires, which, if the apparatus has been properlyadjusted is at the time that the opaque material leaves the right auricle, the train of pulses entering the contactor is stopped, and will remain stopped until the fourth thyratron 48 fires. When the fourth thyratron 48 fires, which, if the apparatus has been properly adjusted, is at the timethat the opaque material reaches the left auricle, the switch 22 is closed by the action of relay 5'8 and pulses are again allowed to enter contactor 8. When the opaque material leaves the left auricle, the fifth thyratron 50 fires and causes the relay'6l) to open the switch 26, thereby preventing pulses from entering the contactor 8. 3

Since a thyratron once triggered will continue .to fire until the anode voltage is removed, each of the tubes, .after having once been triggered, continues to fire, and when the fifth thyratron .commences firing, all five thyratrons will be lfiring. Thus, until some external operation is done to remove the anode potential from the 'thyratrons, the apparatus cannot repeat because the fifth thyratron 50, while firing, causes the .relay 60 vto keep the switch 26 open. A reset switch 62 is provided in the common anode circuit-of the five control thyratrons. When it is desired to prepare the apparatus for another .cycle of operation, the switch 62 connected be- .tween the anodes of the control thyratrons and .their source of anode potential is opened, and .thenallowedto close. -When the reset switch 62 is opened manuallyby the operator, the anode ,potential-is removed from the control thyratrons and they cease to conduct. When the reset switch 62 is closedagain, none of the control .thyratronsare firing, and the apparatus is ready to repeat the cycle whenit is again triggered by grounding thecontrol grid 29 of the first control thyratron tube 28.

The multivibrator I6 employed in a preferred embodiment of our invention is a double multivibrator comprising three tubes. These tubes are, amaster vacuum tube64 having two anode circuits, namely, an originally non-conducting master circuit comprising an anode 6|, a cathode 63 and a grid 68, and an originally conducting master circuitcomprisingan anode 65, a cathode -69 and.a grid 61; a'slave vacuum tube 66 having therein ,two anode circuits, namely, an originally conducting .slave circuit comprising an .anode II, a cathode I5, and a grid 13, andan originally non-conducting slave circuit comprising ananode 1.1, a cathode 8| and agrid I9; and a multivibrator control thyratron tube 83 comprising a cathode 85, an anode 81 and a control grid 09. The master, and the slave vacuum tubes 64, 60 of the multivibrator [6 are connected together in such a manner that the two circuits of the master tube 64 have the grid of each connected so as to be responsive to the plate current of the other, and the grid 13 of the originally conducting slave circuit connected so as to be responsive to the current through the originally non-conducting master circuits 6|, 63, B8 of the master tube 64. Connected to the originally conducting section H, l3, 15 of the slave tube 66, so as to be responsive to the current thereof is a first control grid of the multivibrator control thyratron 83. Connected in series with the cathode B5 of this control thyratron 83 is a condenser and a variable resistance 93 in parallel. Connections are also provided between the cathode 85 of the multivibrator control thyratron 83 and the grid 19 of the originally non-conducting slave circuit ll, l9, 8!. Connected in the latter circuit so as to be responsive to the current therethrough is a relay and a switch 9! responsive thereto. This switch 91' constitutes the output of the multivibrator it for control of the X-ray contactor 8 and the camera.

When the multivibrator control thyratron 03 fires in response to the originally conducting slave circuit 'i l, l3, l5 becoming non-conductive, the control condenser 01 in series with the cathode 85 of the control thyratron becomes charged. When the control condenser 9| becomes charged, there is no longer sufficient plate voltage on the control thyratron 83, to maintain conduction. At the same time the charge on the condenser 83!, which is applied to the grid 78 of the originally non-conducting slave circuit, causes that circuit to become conducting to cause the operation of the multivibrator relay 95. When the charge on the control condenser 9i leaks off through the variable resistance 93 in parallel therewith, the grid T0 of the originally nonconducting slave circuit becomes negative again and that circuit becomes non-conducting. Thus, by adjusting the variable resistance 93, an operator is able to control the length of time the originally non-conducting slave circuit H, l9, 8! conducts and, thereby to control the length of time the multivibrator relay 95 is activated.

Connected between the grid 08 of the master tube 64 and ground is a variable resistor '80 with two movable contacts 15, it. Each of these contacts 16, 78 is connected through a respective pulse control switch 14, 12 of relay 56 to ground. Switch M is open when switch I2 is closed. The magnitude of the resistance between the grid 63 and ground determines the time constant of the multivibrator. Thus, by changing the setting of the variable resistor 10, the frequency of the pulses produced by the multivibrator may be controlled. The pulse control switches 12 and M are operated by the relay 56 in response to firing of the third thyratron 45. Thus, when the apparatus starts to operate, during the period before the third control tube 40 fires, the first pulse control switch 72 is closed and the second pulse control switch 14 is opened. Therefore, the frequency of firing of the multivibrator is determined by the setting of contact 18 on the variable resistor 10. When the third control thyratron tube 45 fires and actuates relay the first switch i2 is opened and the second switch M is closed. When the second switch 74 is closed, the time constant of the multivibrator is determined by the position of contact 16. Thus, when the first switch 12 is opened and the secondswitch 14 is closed in response to the firing of the third thyratron 4B, the time constant of the multivibrator I6 is changed and thereby the rate of firing of the multivibrator is changed.

It is, therefore, possible with our apparatus to cause pictures to be taken at one frequency when the opaque material passes through the first auricle of the heart, and to be taken at another frequency when same opaque'material passes through the second auricle.

It may be desirable, though not essential, to prevent the multivibrator circuit from operating when the pulse generator selector switch I0 is in the electrocardiograph, or camera, position. For this purpose a multivibrator control switch 200 is provided. This switch has three contact positions and is ganged to the selector switch l0 and connected so that when the selector switch is not in the multivibrator position, the switch 40 on relay 202, which is operated by the second discharge device 38, is shunted. When the selector switch [0 is on the multivibrator position, then switch 40 is effective to remove the negative bias from the grid 68 to start multivibrator operation when relay 202 is operated responsive to conduction of the second discharge device. When the third discharge device 40 conducts,

switch 204 on relay 5B closes to shunt switch 40' and stop multivibrator operation. When the fourth discharge device 48 conducts, switch 206 on relay 58 opens to remove the shunt on switch 40, and multivibrator operation again starts.

An electrical connection is provided between the anode ll of the originally non-conducting slave circuit and a second grid of each of the control thyratrons 38, 46, 48, 50. Thus, when the originally non-conducting slave circuit is conducting and thereby activating the multivibrator relay 95, a negative potential is applied to the second grids of the control thyratrons. The negative potential thus applied to the second grids of the control thyratrons prevents these thyratrons from conducting when the originally non-conducting slave circuit is conducting. We have thus provided a means of preventing any of the control switches I2, 20, 22, 26 from operating while an X-ray photograph is being taken in response to the action of the multivibrator output switch 91.

A time delay device, which may be a thermally actuated device 82, is energized from suitable connections to the power supply. The contacts of this device 82 are connected in series with a lamp 09, a switch and an on-off switch, when in the on position, to the main power supply. The delay device 32 therefore provides a time delay which begins when power is first applied to the apparatus. Therefore, when the lamp 99 is lighted, it is an indication that the apparatus is in condition for operation.

The switch 84 is actuated by the relay 60 so as to be responsive to the output current of the fifth thyratron 50. Thus, when the fifth thyratron 50 fires, it causes the switch 04 to open which causes the lamp 99 to go out, indicating that the apparatus is not ready for operation. When the reset switch 62 is opened, and the potential is thereby removed from the anodes of the control thyratrons causing them to cease firing, the relay 66 connected to the fifth thyratron 50 is no longer energized and the switch 84 is allowed to close, allowing current to be again supplied to the lamp acva-cea 98; therebyindicating-to -an*operator. thatntheap paratus is: again-ready for operation.

The switch-24 1s ganged to' the" variable resist ance l68 -inthe time constant-- network: of the fifth discharge device 5am: a manner such that:

the switch 24 will be opened when the variableresistance isset to-zeroi Thus,-. when there is to be-no-time interval for -the taking: of exposures 01" the'second auricle, then the switch z l is open and the contactor cannot be energized after the third discharge-device -46 conducts.

A test circuit is provided for: showing toan,

operator bythe fiashingof alight, the timing sequence for which the apparatus has beenset. The test circuit comprises a lamp 86, connected to'pne'side of the main power supply and: connected through a test switch 88 to which is-applied the output electric pulseswhich would nor mallygo-to the X raycontactor. Biif the switch 881 were in the operatepositionas shown, instead of in the-test position. The test switch Stdsgangedwiththe switch 80 and it follows therefore that whenthe switch 88- is in the testposition; the

switch 89 is open, therebylbreakingthe circuit-to Since numerous changes may be made in the above-described construction and different ems bodimentsof the-invention may be made without. departing from the spiritand scope thereof, it is intend'edthat all'matter contained: in the foregoing descriptionor shown in the. accompany.-

ing drawing, shall be interpreted as illustrative.

and not in a limiting sense.

We claim as our invention:

1. In combination, anX -ray generating apparatus, a multivibrator, a relay connected torsaidi multivibrator so asto be'responsive to .the current;

therethrough, a first switch adapted to be op-- erated by said relay, electrical connections be-- tween oneside of said=switchand said apparatus, current supply connections connected to the otheiv side of said switch for supplying. current to said; switch, a plurality of electric discharge devicessoconnected that eachsucceeding discharge device is rendered conductive in response to conduction of the discharge-device immediately preceding, a terminal for applying a negative bias potential, connections between-the grid-ofa first of said electricdischarge-devices and'saidterminal, said last mentioned connections including a resistor, connections for grounding said grid so asto cause-'- said first electric discharge device to fire; connections between the output of a second of said plurality of discharge-devices and a second relay so that saidrelay is responsive to the output cur-- rent of said second discharge device, a switch. energized by said second relay, said switch being connected on one side to ground and onthe other side through one of a first resistance, or. alternatively through av second resistance,tto a grid of: said. multivibrator, whereby said switch is capable of selecting the frequency of operation of saidimultivibrator.

2. In combination, an X-ray generating apparatus, a multivibratcr, a relay connectedto said multivibrator so as to be responsive to the current therethrough, a first switch adapted to be operated by said relay, electrical connections betweenone side of said switch and said apparatus, current supply connections connected to the other side of said switch for supplying current to said switch, a plurality of electric discharge devices so connected that each succeeding discharge device is-rendered conductive in response to conduction of the dischargedevice immediately preceding, a; terminal: for. applying anegativei bias: potential, connections between the gr-idlof afirst of saidelectric discharge devices and said. tel.- minal, said lasts-mentioned, connections includinzl a resistor, connections for grounding said: grid: soas to cause said. first electric dischargedevice.

tofire; connections between theoutput: of a. sec.-

0nd of said plurality of discharge devices; and:

a. second: relay so that said: relay is responsive: to, the output, current of, said second discharge: de-

and on the other side to a terminal which isnegative with respect to ground, connections for an plying a positive potential to' the anodes of said electric discharge. devices, a reset switch irrseries, with said connections for disconnecting the source;

of said positive potentialfromsaid anodes.

3. In combination, an X-ray generating apparatus, a multivibrator, a relay connectedito said multivibrator so as to be responsiveto the current therethrough, a first switch adapted tobe operated by said relay, electrical. connections;

between one side of said switch and saidapparatus, current supply connections connected, to the other side of said switch for supplying cur.- rent to said switch, a plurality. of electric dis:-

charge devices so connected that. each succeed ing discharge device is rendered; conductive in:

response to conduction, of. the discharge deviceimmediately preceding, a. terminal for applying:

anegative bias potential; connections 'betweenthe:

grid of a first of said electric discharge device, and said terminal, said last-mentioned connections including a resistor,.connections for ground-- ing said grid so as to cause said first electric discharge device to fire; connections between the:

output of a second of said plurality of dischargedevices and a second relay so that said relay is responsiveto the output current ofsaid-isecond'r discharge device, a switch connected to said'secrond relay so, as tooperate in response thereto,,

said switch being connectedon oneside-through:

a first'resistance; or alternatively through a seer ond resistanceto ground, and also to; agrid-of. said multivibrator, connections for supplying; a current to the filament of atleastone of said discharge device, saidv last-mentioned connections including apparatus for indicating when a cur rent has flowed through the filament of. said: last-mentioned discharge device'for a predetermined periodv of time;

4. In combination, an X-ray. generating an.- paratus, a multivibrator, a relay connected to said multivibratorso as to be responsive to the. current therethrough, a first switch adapted to.- be operated by said relay, electrical connections between one side of saidswitch. and saidan par-atus, currentsupply. connections connected to, the other side of said' switch for supplying current to said switch, a plurality of electric dis-- charge devices connected together so that each succeeding discharge device is caused to consecond of said plurality of thyratrons and a secswitches connected to said second relay so as to operate in response thereto one of said switches I being open when the other is closed, said switches being connected on one side to ground and on the other side through first and second resistances respectively, to a grid-of said multivibrator, connections between said grid of said multivibrator to a source of negative potential, whereby said switch is capable of selecting the frequency of operation of said multivibrator, a test light, a switch connected to said test light and connected in the circuit of said first-mentioned connections for allowing the current from said source to pass through said apparatus, or alternatively to pass through said light.

5. In combination, an electrocardiograph, apparatus for producing Xrays, a plurality of electric discharge devices, connections to a first of said electric discharge devices for triggering said first device, connections between said first device and a second of said electric discharge de-,

vices for rendering said second device conductive in response to conduction of said first device, said last-mentioned connections including a capacitor and a resistor for effecting a time delay between the firing of said first device and the firing of said second device, switching meansconnected to said second electric discharge device so as to be responsive thereto, electrical connections between said electrocardiograph and said switching means, electrical connections between said switching means and said apparatus.

6. In combination, an electrocardiograph, apparatus for producing X-rays,'a plurality of electric discharge devices, connections to a first of said electric discharge devices for triggering said first device, connections between said first device and a second of said electric discharge devices for triggering said second device, said last-mentioned connections including a capacitor and a resistor for effecting a time delay between the firing of said first device and the firing of said second device, switching means connected to said second electric discharge device so as to be responsive thereto, electrical connections between said electrocardiograph and said switching means, electrical connections between said switching means and said apparatus, said switching means being operable responsive to conduction of said second device so that the circuit through said switching means is closed and current from said electrocardiograph is allowed to flow through said switching means to said apparatus, means for operating said camera in response to an electric current, connections between said switching means and said means for operating said camera so that at least part of the current through said switching means passes through said means for operating said camera.

7. Apparatus as is described in claim 6 wherein a third of said plurality of electric discharge devices is connected to said second device so as to be rendered conductive in response to the conduction of said second device, a second switching means connected to said second device so as to be responsive thereto, said second switching means being connected in thecircuit between said electrocardiograph and said apparatus for generating X-rays so that said second switching means opens that circuit when activated by said third electric discharge device.

8. An X-ray apparatus comprising an X-ray 10 generator control contactor, connections for applying a potential to said control contactor so as to activate said contactor, a first switching means, a first time delay circuit connected to said first switching means so as to be responsive thereto, a second switching means connected to said first time delay circuit so as to be responsive to the current therethrough, a second time delay circuit connected to said second switching means so as to be responsive thereto, a third switching nreans connected to said second time delay cir- 4 sponsive to the current therethrough, said second switching means being connected to said connections for applying a potential so as to close the circuit of said connections when said second switching means is activated, said third switching means being connected tosaid con- ,nections so as to open the circuit of said connections when said third switching means is activated, said fourth switching means being connected to said connections so as to close the circuit of said connections when said fourth switching means is activated, said fifth switching means being connected to said connections so as to open the circuit of said connections when said fifth switching means is activated.

9. In apparatus of the type wherein an X-ray generator is operated responsive to operation of a contactor having an energizing circuit, and a control circuit controls the condition of said energizing circuit, the combination with said control circuit of a multivibrator, a relay connected to be operated responsive to the action of said multivibrator, a switch controlled by said relay, said switch being connected in series with said contactor energizing circuit, a plurality of electric discharge devices, means for causing said discharge devices to become conductive in succession, a relay associated with each of said discharge devices so as to be operated responsive to conduction of its associated discharge device, a switch controlled by each of said relays, each said switch being connected in series with said contactor energizing circuit, and means for preventing said discharge devices from becoming conductive when said switch which is responsive to the action of said multivibrator is in the closed position.

10. In apparatus of the type wherein an X-ray generator is operated responsive to operation of a contactor having an energizing circuit, and a control circuit controls the condition of said energizing circuit, the combination with said energizing circuit comprising a multivibrator having two predetermined operating frequencies, a switch nected in series with said contactor energizing circuit, and a' 'furtherswitchadevicez associated discharge devices so as tobe operated responsive to a change inzthe'state of: conduction of'its'associated discharge: device, each said; switch. de-

vice .being connectednn: series: saidicontactor energizing circuit, and .a furtherswitch' device associated with each:of;the:first; second and third discharge devices of said succession, said further switch devices being; connected: to control the starting andrstoppingi of'zsaid multivibrator;

12 12: In;apparatusrof:the'typerwhereinan.Xqmy generator/is: operated responsiveuto: operation; of a contactoit having anxenergizing circu1t,.and :a control circuitcontrols thecondition of said'energizing circuit; thecombination with'said energizingcircuit'comprising an electrocardiographshev- .ingcoutputterminal's connected inseries withisaid contactor energizingr circuit, a plurality'oi' electric discharge, devices; meanstfor causing saididischarge :devices. to become conductive in delayed succession, a switch device associated with each of said: discharge devices so as to be operated responsive'toachange inthestate of conductionrof its associated discharge device, each said switch devicebeing connected inrseries with said con- 'tactor energizing circuit;

References Cited in the file of thispatent UNITED STATES PATENTS Number. Name Date,

2190;389' Strausset a1 .;E.eb. 1'3, 1940 2,392,114 Bartelink Jan. 1, 1948 2,476,882 Lexa July 19,1949 2,489,860 Carlin Nov. 29, 19.49 2,526,421; Riggs Oct. 1.7; 1950 2,544,716 Nier Mar. 13, 195.1

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