US2752509A

US2752509A - X-ray apparatus and controls

Info

Publication number: US2752509A
Application number: US183019A
Authority: US
Inventors: Charles T Zavales
Original assignee: F R MACHINE WORKS
Current assignee: F R MACHINE WORKS; F-R MACHINE WORKS
Priority date: 1950-09-02
Filing date: 1950-09-02
Publication date: 1956-06-26
Anticipated expiration: 1973-06-26

Description

4 Shets-Sheet l 772/6652 GEA/62am@ 77/7575 C/zCl//T INVENTOR lo pfsrr,

ATTORNEY C. T. ZAVALES X-RAY APPARATUS AND CONTROLS C. 7". ZHVLE'S.

BY A@ U. c'. sugar 551-177 WMF@ 7260/7 June 26, 1956 Filed Sept. 2, 1950 June 26, 1956 c. T. zAvALEs 2,752,509

X-RAY APPARATUS AND CONTROLS Filed Sept. 2, 1950 4 Sheets-Sheet 2 .f-:EzE-rg' 5.8 (61) Meagan/Mm? BY Ang elo M. @15am-L ATTORNEY June 26, 1956 c'. T. zAvALEs 2,752,509

x-RAY APPARATUS AND CONTROLS Filed Sept. 2, 1950 4 Sheets-Sheet 3 I I I I I I TUBE 96 I I I 130 fwn/e655 V02 7765 o/v Rufzo w55 196 II A INVENTOR c'. 7*. ZAL/H255.

Abgeo yl, plsaH-a ATTORNEY June 26,' 1956 C. T. ZAVALES X-RAY APPARATUS AND CONTROLS Filed Sept. 2, 1950 4 Sheets-Sheet 4 I 1 195 A i m 171 j .1M

l @j i fr s 194 142,. 130 .775 gg I A l101 /19g i al Z 4 5 a v50-1^ 195 l o l Lew l 190 111 j Mz 15@ .nl 201 l M/Q! 205 l v I l 51 @L i J l M /l/ f 1 .1 j J IL ...4246 l a3/1 01 il "IPM-IWW l 15 l INVENTOR i Cffzmfufs. BY psavra. L IAmge/o n ATTORNEY United States Patent X-RAY APPARATUS AND CONTROLS Charles T. Zavales, New York, N. Y., assigner to F-R Machine Works, a firm Application September 2, 1950, Serial No. 183,019

10 Claims. (Cl. Z50-95) This invention relates to X-ray apparatus and to novel controls. In one of its more specific aspects the invention is directed to novel X-ray timers.

In one of its main features the control includes a pair of main thyratrons arranged back to back and circuit interlocked as to be dependent upon each other for operation, so that if one fails in its operation, the other will not operate or re in the next succeeding half cycle. Still another main feature is a continuous safety timer to protect each timer setting in the event of failure of the main timing circuit. Still another main feature is the provision of a feed back transformer for synchronizing operation so that the main thyratrons are interlocked as before set forth. Another main feature for controlling of the tiring of the main thyratrons by a spike voltage applied to the grid of the main thyratrons at predetermined times.

Still another feature of this invention is a timer so that an even number of half cycles are obtained in a load circuit. This is of particular importance so that the residual magnetism in the core of the X-ray transformer is in the proper direction for the exposure to follow. To eliminate the possibility of making an odd number of half cycle exposures a voltage obtained from a synchronizing transformer within the timer unit is superimposed on the voltage that is stored in the main timing condenser. The magnitude of this voltage or spike is arranged so that it is a little less than the step which will follow during the next half cycle. This arrangement eliminates the possibility of half cycle error in the timer as it results in a premature firing of a control tube. These and other features of the invention will be readily apparent from the following description and drawings, wherein:

Fig. 1 represents a wiring diagram of an X-ray apparatus embodying the invetnion.

Fig. 2 represents a wiring diagram of a trigger generator for sharpening the voltage supply from a phase shifter to be applied to the grid of a main thyratron which controls the main circuit as shown in Fig. l.

Fig. 3 is a wiring diagram of a synchronizing control and safety timer.

Fig. 4 is a wiring diagram of the main timer.

Figs. 5 and 6 are a pair of graphs showing the main timing condenser voltage-time and its relation to the conducting and triggering cycle of the main thyratrons.

As shown in the drawings, there is an X-ray tube having an anode 8 and a thermionic cathode 9. This X-ray tube 10 is to receive high voltage, uni-directional electric energy from a full wave rectifying arrangement 11 connected thereto and also to a secondary winding 12 of a high voltage transformer 13. The mid point of said secondary winding 12 of the high tension transformer 13 is grounded at 14. One end of the primary winding 7 of the transformer 13 is connected to one end of an auto transformer 1S by conductor 16. The other end of the primary winding 7 is connected by conductor 17 to the mid point of a secondary winding 18 of a filament heating lice transformer 19 of a main thyratron tube 20 having anode 21, cathode 22 connected across winding 1S and grid 23. The anode 21 is connected by conductor 2S to a contact of a normally open switch 26 whose other contact is connected by conductors 27 to adjustable contact 23 of said auto transformer 1S which is supplied with electric energy from the input line 30 having live switch 29.

For current conduction in the load circuit during the next half cycle, anode 32 of a second main thyratron 33 is connected to conductor 17. Thyratron 33 has a thermionic cathode 34 similar to cathode 22, and a grid 3S. The cathode 34 is connected across the secondary winding 36 of a filament heating transformer 37. A conductor 38 is connected to the conductor 25 and to the mid point of the secondary winding 36.

The thermionic cathode 9 of the X-ray tube 10 is connected across the secondary winding of the lament heating transformer 40, whose primary is vconnected to a filament stabilizer 41 having

input lines

42 and 43 connected to the auto transformer 15. Primaries of the filament transformers 19 and 37 are connected in multiple and directly across the

conductors

42 and 43 by

conductors

44 and 45.

A phase shifting circuit 47 includes a condenser 5t) and a variable resistor 51 connected in series and also another similar combination of condenser 52 and variable resistor 53 connected in series. An output conductor 5S is connected at the mid point between condenser S2 and resistor 53 at one end and its other end to the input of a trigger generator S6 for sharpening the phase shifter voltage.

The output of generator 56 is connected by conductor 58 to grid 23 of thyratron 20. A conductor 59 is connected to the mid point between condenser Sil and resistor 51 and to the input side of a similar trigger generator 66 whose output side is connected to the grid 35 of thyratron 33 by conductor 61. The phase shifting circuit has

input li'nes

63 and 64 connected to the auto transformer 15 through

conductors

42 and 43, with a double pole, double throw switch 65 in the supply line to supplyabout 115 volts to the phase shifter.

The output line 55 of said phase shifter is connected to a thermionic cathode of a rectifier tube 67 through a coupling condenser 66. A resistance 68 is connected between the coupling condenser and the retifier 67 to ground. The anode of the rectifier 67 is connected to grid 70 of ampli'er tube '71 and also to ground through a resistance 69. The plate of tube 71 is connected to the grid 72 of amplifier tube 73 through a coupling condenser 74. The plate of tube 73 is connected to the grid 75 of amplifier tube 76 through a coupling condenser 77 and a resistor 78. The grid 75 is connected to a negative voltage of volts by supply line 79 through a resistor 80.

The plate of tube 76 is connected to grid 31 of tube 82 through coupling condenser 83. The plate of the tube 82 is connected to one side of the primary winding 85 of a trigger transformer 86 through a coupling condenser 87. The other side of the primary winding of trigger transformer 36 is connected to ground, as are the thermionic cathodes of the four amplifier tubes.

Grids

70, 72 and 31 are also connected to ground through resistors. The plates of all of said amplifier tubes are all connected to a source of plus 250 volts through a common plate supply line 90.

A rectifier tube 91 is connected across the terminals of the secondary winding 92 of the trigger transformer 86. The anode end of the winding 92 is connected by line 93 to the negative terminal of the bias supply for thyratron v20. The cathode side of the winding 92 is connected to the grid 23 of thyratron 20 by conductor 58. The mid point of the secondary winding 18 is connected by conductor 94 to the positive terminal of the 45 volt bias supply for thyratron 20. A condenser 95 is connected between grid 23 and the center tap of Winding 18.

The trigger circuit 60 is the same as trigger circuit 56, hereinbefore described in detail, and has a supply line 95 similar to 79; a supply line 96 similar to line 93; and a line 97 connecting the mid point of the secondary winding 36 to complete the grid circuit of the thyratron tube 33. A synchronizing control and safety timer 98, illustrated in Fig. 3, has an input line 99 connected through a resistor to the grid of a gate thyratron 100 and to one end of the secondary winding of a feed back transformer 101, which secondary winding is grounded at its mid point. The thyratron 100 has a thermionic cathode connected to ground through a resistor, thus completing the grid circuit of said tube 100. The other side of the secondary winding of the transformer 101 is connected by conductor 102 through a resistor to the grid of a gate thyratron 103, whose thermionic cathode is connected to ground through a resistor. The anodes of gate thyratrons 100 and 103 are connected by line 107 through a resistor to contact 108 of a normally open relay switch 109. Switch 109 receives its energizing power through

lines

110 and 111. Line 110 (Fig. 1) is connected to one Contact of a normally open switch X whose other contact is connected to line 43. Line 111 is directly connected to supply line 43 to cornplete the circuit for said relay 109. A plus 105 volt anode supply line 117 is connected to the other contact of said normally open single pole switch 108.

A relay 115 for completing the primary circuit to transformer 13 is connected to line 42 by line 114 and to line 43 through a normally closed push button switch 112, a normally open push button switch 113, line 158, normally closed contacts 127 on relay 126 and line 159. The relay 115 is provided with a pair of auxiliary contacts for by passing the normally open push button 113 for interlocking relay 115 after the switch 113 is rendered operable.

Another relay 120 of a switch 121. is connected across the

supply lines

110 and 111 by

lines

122 and 123. Line 107 supplies anode voltage to a thyratron 124 through a resistor 125 and relay 126 of a normally closed switch 127. A condenser 128 is interposed between said anode and ground. Anode voltage is likewise supplied through line 107 to the anodes of

control tubes

130 and 131. The cathodes of tubes 100 and 103 are connected to ground line 132 through resistors, whereas the cathodes of tubes through a resistance 155. The normally closed contact 156 of switch 121 is connected to line 157 supplying grid bias for safety timer thyratron 136 when switch X is open and relay is inoperative. The controlling action of the thyratrons 100 and 103 through

lines

99 and 102 is determined by the feed back transformer 101, which is connected across the primary of the high tension transformer 13 through lines 160 and a double pole-double throw switch 162 for phasing purposes. The purpose of this feed back circuit is to prevent normal operation of either of the main thyratrons 20 and 33 in the event that the other fails. The circuit to accomplish this and the timer circuit, including the bias supplies for the safety timer thyratron 124 and the 30 volt bias supply for

thyratrons

100, 103, and 131 through line 104, arc indicated in block form as 165 in Fig. 1.

Referring to Fig. 4, there is a control tube 166 having its cathode connected to line 99. A second control tube 167 has its cathode connected to line 102. The anode of tube 166 is connected to the grid 168 of a tube 169 and through a resistance 170 to ground. The anode of tube 167 is connected to the grid 171 of a tube 172 and also to ground through a resistance 173. The anodes of

tubes

169 and 172 receive power through a plus 250 volt supply line 174, each through suitable resistances 175. Line 174 is connected to line 90 (Figs. 1 and 2). The anodes of

tubes

169 and 172 are also connected to opposite ends of a circuit at points 177 and 178, through condensers 179 and 180. This circuit includes

rectifiers

181, 182, 183 and 184. The cathode end of rectifier 182 connects to line 185, to the primary 186 of a synchronizing transformer 187 and then to the cathode of tube 184 through line 188. Line connects to timing

condensers

190 or 191 through line 192 and a contactor 193 and back to ground. Line 185 connects also to the secondary 194 of transformer 187, line 195 and the anode of a thyratron 196. The cathode of thyratron 196 is connected to ground through resistance 197 and through a coupling condenser 198, line 199 direct to the grid 133 of tube 131 (Fig. 3). The control grid 200 of thyratron 196 connects to contactor 201 through line 202 to a bank of various resistanccs 205 connected through a contactor 206 to a voltage divider 207 through line 208. An open switch 210 connects condensers and 191 across to ground. A contactor 203 of a fixed potentiometer 215 is connected to contact 156 of switch 121 through resistance 216, line 204 and line 157.

Operation The main line input switch 29 is closed to bring the line 30 in operation to energize the auto transformer and also the iilament 9 of the X-ray tube through the stabilizer 41 l also to energize the phase shifter 47, power supply 147,

denser 145 connects across grid 142 and anode supply line 107. Grid 144 of tube 130 is connected to the cathode and through a variable resistance 745, to a -150 volt bias supply line 146.

Supply lines

90, 117 and 146 are directly connected to a conventional voltage supply 147, which receives power from incoming supply lines 148, leading to the X-ray ilament stabilizer 41, which in turn receives its power through

supply lines

42 and 43 by transformer 15. A variable contact 147 of resistor 145 receives the bias for the control tube 76 of trigger generator 56 through line 148 which is connected directly to line 79. A variable contact 150 recives the bias for the control tube of trigger circuit 60 through line 151 which is connected directly to line 95. Said contact 150 is part of Variable resistance 152, which is connected across -150 volt bias supply through line 146 and the cathode of thyratron 100.

The contact 154 of switch 121 is connected to line 107 synchronizer control and safety timer 98, timer 16S, as well as the

trigger generators

56 and 60 and also the bias supply for main thyratrons 20 and 33.

Then the apparatus is first conditioned by push button 113 which is pressed down to complete the primary circuit to the high tension transformer and as a result of this action the switch 26 is closed by virtue of energization of the winding 115. Now the mechanism is set for making an exposure of the desired length of time. The four-deck tandem switch S is adjusted for the desired exposure time. This action pre-sets the bias voltage on grid 200 of thyratron 196 and connects the proper timing condenser either 190 or 191 into the timing circuit and it also pre-sets the bias voltage on the grid 136 ot' the thyratron 124 of the safety timer.

The output of the phase shifting circuit 47 is fed into the trigger generator 56 by a line 55 directly through the coupling condenser 66 to the rectifier 67. The output of the tube 67 is fed to the grid 70 of the amplifier tube 71 and the voltage developed across the resistor 69 is negative with respect to ground. This voltage causes the tube 71 to become cut off and in so doing makes the plate of the tube 71 become more positive. Consequently, the positive going plate of tube 71 in turn will cause the grid 72 of the next succeeding amplifier 73 to become more positive and the voltage of the plate of tube 73 will in turn become less positive. This action would normally tend to cause the grid 75 of the gate amplifier 76 to become negative and thereby vary the plate current in amplifier tube 76. In order to render the tube 76 completely inoperative a negative voltage of -85 volts is applied thereto by line 79 to resistor S0 from the circuit 98. Negative pulses are continuously applied to the grid 75 from the phase shift supply 47 as hereinbefore explained. The gating action of amplifier 76 of trigger generator 56, because of the high negative bias, prevents any trigger voltage from appearing across the primary of transformer 86. Since the grid 23 of thyratron 20 is being held at 45 volts by the bias supply for thyratron 20, thyratron 20 can not become conducting until a positive voltage appears across transformer 36. A phase shift voltage is obtained from lead 59 which is 180 degrees out of phase with respect to the voltage on lead 55 and is the input to the trigger generator 60 whose tube corresponding to tube 76 is maintained in the same condition as tube 76, as heretofore described, to prevent the grid 35 of thyratron 33 from going positive, thus preventing the tube 33 from firing. This condition is maintained until switch X is closed. Then switch X is closed for initiating the exposure. When yswitch X is closed the following circuits are made: From the auto transformer 15 through line 43, switch X, line 11b, relay 109, line 111 back to 42 connected to the auto transformer. At the same time relay 120 is energized in that it is in parallel with relay 109 through

conductors

123 and 122. The normally open switch 109 is closed upon the energization of the relay to apply plus 105 volts to each of the anodes of

thyratron tubes

131, 124, 100, 163 and 130 through line 117, relay 109, contact 108 and line 1177.

The positive 105 volts i-s also applied to the grid 142 of the thyratron tube 130 through condenser 145, in order to render tube 130 conducting. When tube 130 becomes conducting, a positive voltage of approximately 80 volts with respect to ground appears at its cathode. The positive voltage of 80 volts, which appears across the cathode resistor of tube 130, is applied to the potentiometer 145, which determines the bias for the grid 75 of tube 76. Prior to the time that tube 130 breaks down and all through its operation, a negative voltage of approximately 150 volts is applied to the other end of potentiometer 145, which is adusted to produce a negative bias of approximately --85 volts on the grid 75 of tube 76. Breakdown of thyratron 130 causes the voltage of the arm 147 of potentiometer 145 to become less negative so that the voltage on line 79 wiil be changed to approximately -25 volts. This reduction in bias on grid '75 of tube 76 now allows the tube to become conducting and thereby produces a positive pulse across the primary 85 of transformer 86 through amplifier tube 82. Since the secondary 92 of transformer S6 is in series with the bias supply line 58 for grid 23 of tube 20, the presence of a positive voltage across the secondary winding 92 will be superimposed on the -45 volts grid bias to cause tube 20 to fire and to complete the primary circuit of the high tension transformer 13, one-half cycle for the generation of X-rays during that half cycle. This tube 130 merely initiates energization of the high tension transformer for the first half cycle only.

The feed back transformer 101 is so polarized that line 99 becomes positive when tube 20 is conducting. This causes the grid of tube 100 to become positive and thereby results in a breakdown and operation of the tube. A coupling condenser 561B which is connected between the cathode of tube 100 and the cathodes of

tubes

103 and 130 causes tube 130 to become non-conducting as soon as tube 191i breaks down. As soon as tube 130 becomes nonconducting, the grid 75 of tube 76 again becomes highly negative at approximately volts to render it nonconducting so that no positive trigger potential is applied to the grid 23 of tube 20. By the pre-adjustment of the potentiometer 152. one end of which is at -150 volts from the D. C. supply through line 151, a potential of 85 volts is applied to the grid of the tube 76 in the trigger circuit 60. With tube conducting, the cathode thereof becomes positive and, consequently, the voltage of the line 151 and of the grid 75 of circuit 60 becomes approximately -25 volts. This changing of voltage from --85 voits to -25 volts prepares tube 33 for conduction for the next half cycle. When tube 33 becomes conducting, line 102 will also become positive and causes tube 103 to become conducting. This action will cause tube 100 to become non-conducting through coupling condenser 506. This action prepares the trigger circuit 56 for operation during the next positive half cycle. This action continues back and forth as shown in Fig. 6 and until a positive pulse is applied through

leads

149 and 142 to re tube 131. This action terminates the exposure. This is done by reducing the voltage on the plates of

tubes

124, 100, 103 and 130 to approximately 20 volts, thus effectively shortcircuiting these tubes. Tubes 100, 103 and comprise an interlocked circuit which controls triggering of

tubes

20 or 33. This interlocking is provided to prevent operation of the high transformer 13 on D. C. in the event that either

tube

20 or 33 fails to become conducting. The circuit automatically provides this protection by virtue of the flip flop action which occurs between tube 100 and 103, That is to say that the tube which controls the triggering of a

particular thyratron

20 or 33 automatically becomes inoperative, after having brought about the triggering of the particular thyratron (20 or 33) that it controls. if thyratron 20 is triggered for a half cycle and the other is not triggered in its next succeeding halt cycle, then thyratron 20 will not be triggered in the immediately following half cycle of the same polarity. Relay 120, which operates in parallel with relay 109, initiates the safety timer which is made up of tube 124 and relay 126. Prior to operation of relay 129, condenser becomes charged to a pre-set negative voltage through lead 157 and lead 204, resistor 216 and by the positioning of an adjustable contact 203. After relay 120 operates, condenser 140 is connected through contact 154- and resistor 155 to the positive 105 voit supply through contact 103 on relay 109 and lead 117. This causes condenser 140 to Istart becoming charged positive, that is, it becomes less negative. After this condenser has reached a predetermined voltage, the grid 136 of' tube 124, which is connected through resistor 138, causes tube 124 to become conducting thereby operating relay 126 which is connected in its plate circuit. Operation of relay 126 causes relay 115 to fall out and thereby open the primary circuit to the high tension transformer. The magnitude of negative voltage to which condenser 140 becomes charged determines the length o-f time that it takes for this action to occur, and in normal operation of the timer this time is set for approximately one cycle longer than the exposure time pre-set by switch S. The safety timer i-s automatically de-energized when tube 131 breaks down, because this action short circuits the plus 105 volts supply which charges the condenser when relay 120 is energized. The timing is controlled by the positioning of contact 193 and

contacts

201 and 206 on switch S. The contact 193 selects the value ot' capacitor (190 or 191) which is connected in the timing circuit.

Contacts

206 and 201 select the value of negative bias which is applied from lead 202 to the grid 200 of tube 196. Lead 99, which connects to the cathode of tube 166, is so polarized that it becornes positive when tube 20 becomes conducting. The presence of positive voltage on the cathode of tube 166 will cause the grid 16S of tube 169 to become cut off. Condenser 179, which is connected to the 250 volt positive supply through resistor and lead 174, will charge through tube 182 and line 185 through line 192 and con- `artesanos denser 190 or 191 back to ground. Condenser 179 is considerably smaller in capacitance than either

condenser

190 or 191, and it therefore charges to nearly 250 volts (through condenser 190 or 191) in a very short time. The amount of energy stored in condenser 179 is the same as that stored in 199 or 191. Since the time constants, resistor 175 and condenser 179, are small, condenser 179 will become fully charged during the time that lead 99 remains positive.

During the next half cycle, when lead 102 becomes positive, condenser 179 will discharge through tube 181 and tube 169. This will occur because the grid voltage on tube M9 becomes zero. With lead 102 in a positive condition, the grid 171 of tube 172 now becomes negative so as to allow condenser 180 to charge through resistance 175 and lead 174 through tube 184, lead 188 and the primary 186 of the synchronizing transformer 187 through line 192 and contacter 193 through condenser 194B or 191 to ground. The purpose of including the primary 185 of transformer 187 in the charging circuit for the negative half cycle of primary voltage is to minimize timing errors7 and to prevent the occurrence of transients that Will occur in the event that the residual magnetism in the core is not in the proper direction for the exposure to follow. This is shown more clearly in Fig. 5. The presence of this transformer 187 causes a Spike to occur on the leading edge of the waveform which results when condenser 180 becomes charged. The magnitude of this spike is controlled by the value of resistance connected across the secondary 194 of transformer 187. This value is adjusted to be slightly less in magnitude than the step which results when condenser 179 charges. The step like charging of the

condenser

190 or 191 continues as shown in Fig. 5 until the sum of voltage across

condenser

190 or 191 and the spike produced across the secondary 194 of transformer 137 reaches a value that is sufficiently positive to cause tube 200 to break down. Breakdown of this tube results in a discharge of condenser 19t) or 191 through the secondary 194 of transformer 187 through lead 19S, through the plate circuit of tube 196 to ground through resistor 197. The discharge through this circuit causes a voltage drop to appear across resistor 197 which is in turn coupled with condenser 198 and lead 199 through lead 142 to the grid 1.33 of tube 131, so as to terminate the exposure.

I claim:

l. An X-ray tube transformer coupling with an X-rrty tube and in combination with a control for said transformer, said control comprising a pair of thyratrons connected back to back, a pair of negative voltage bias supplies connected to the grids of said thyratrons, a phase shifter, a pair of trigger generators connected to said grids and to the output of said phase shifter, means for controlling the operation of said trigger' generators, said trigger generators responsive to said means to superimpose voltage from said phase Vshifter to said grids to render said thyratrons alternately operative.

2. A timer for a circuit including an X-ray tube transformer comprising a pair of thyratrons connected back to back, a pair of trigger generators, negative voltage bias supplies for the grids of said thyratrons, a phase shifter connected to each of said trigger generators, said grids of said thyratrons connected to said trigger generators, said trigger generators electronically sharpening the input from said phase shifter and applying it to the grids of the thyratrons, a synchronizing feed back transformer for connection across said X-ray tube transformer, a synchronizing control electrically connected to said synchronizing transformer for controlling the operation of said trigger generators.

3. A control for a circuit including an X-ray tube transformer comprising a pair of thyratrons connected back to back, a pair of negative voltage bias supplies for the grids f said thyratrons, a phase shifter, a pair of trigger generators connected to said phase shifter and to said A 8 grids for sharpening the input from said phase shifter and for superimposing a positive voltage on the grid bias for said thyratrons, each of said trigger generators including a pulse transformer and a gate tube for controlling the passage of the sharpened voltage from the phase shifter to said pulse transformer connected to said grids.

4. An X-ray tube transformer control comprising a pair of thyratrons connected back to back, a pair of negative voltage bias supplies connected to the grids of said thyratrons, a phase shifter, a pair of trigger generators connected to the output of said phase shifter for sharpening the voltage from said phase shifter, said trigger generators also connected to the grids of said thyratrons, a feed back transformer, a timer energized by said feed back transformer and a synchronizer also controlled by said feed back transformer, said trigger generators controlled by said synchronizer and responsive thereto for alternately superimposing a positive voltage on said negative bias grids for firing said thyratrons and for suppressing said superimposition of said positive voltage on the grid bias of one of said thyratrons when the other thyratron was inoperative in the preceding half cycle.

5. An X-ray tube transformer control comprising a pair of thyratrons connected back to back, a pair of negative voltage bias supplies connected to the grids of said thyratrons, a phase shifter, a pair of trigger generators connected to the output of said phase shifter for sharpening the voltage of said phase shifter, said trigger generators also connected to said grids, means for controlling the operation of said trigger generators to superimpose the sharpened voltage onto said grids to render said thyratrons alternately operative, and a timer, said timer including a condenser, said means responsive to the voltage built up in said condenser to suppress superimposition of said sharpened voltage on said grids.

6. An X-ray tube transformer control comprising a pair of thyratrons connected back to back, a pair of negative voltage bias supplies connected to the grids of said thyratrons, a phase Shifter, a pair of trigger generators connected to the output of said phase shifter for sharpening the voltage from said phase shifter, a feed back transformer, synchronizing controller connected to said trigger generators and to said feed back transformer, said trigger generators being responsive to said controller to superimpose said sharpened voltage on said grids to render said thyratrons alternately operative, a timer, said feed back transformer connected to said timer, said timer including a condenser, said condenser receiving a predetermined charge during the firing of each of said thyratrons during each half cycle.

7. An X-ray tube transformer control comprising a pair of thyratrons connected back to back, a pair of negative voltage bias supplies connected to the grids of said thyratrons, a phase shifter, a pair of trigger generators connected to the output of said phase shifter for sharpening the voltage from said phase shifter, a feed back transformer, synchronizing controller connected to said trigger generators and to said feed back transformer, said trigger generators being responsive to said controller to superimpose said sharpened voltage on said grids to render said thyratrons alternately operative, a timer, said feed back transformer connected to said timer, said timer including a condenser, said condenser receiving a predetermined charge during the firing of each of said thyratrons during each half cycle, and also a synchronizing transformer for adding a spike voltage to the condenser only during the negative half cycles of conduction of said thyratrons.

8. An X-ray tube transformer control comprising a pair of thyratrons connected back to back, a pair of negative voltage bias supplies connected to the grids of said thyratrons, a phase shifter, a pair of trigger generators connected to the output of said phase shifter for sharpening the voltage from said phase shifter, a feed back transformer, synchronizing controller connected to said trigger generators and to said feed back transformer, said trigger generators being responsive to said controller to superimpose said sharpened voltage on said grids to render said thyratrons alternately operative, a timer, said feed back transformer connected to said timer, said timer including a condenser, said condenser receiving a predetermined charge during the firing of each of said thyratrons during each half cycle, and also a synchronizing transformer for adding a spike voltage to the condenser only during the negative half cycles of conduction of said thyratrons, and means responsive to the sum of the condenser and spike voltages to effect the operation of said controller, whereby said controller suppresses the superimposition of said sharpened voltage on said grids.

9. An X-ray transformer tube circuit coupled with an X-ray tube and in combination with a safety timer including a condenser charged to a predetermined negative voltage and means for reducing said negative voltage when the X-ray tube transformer circuit is closed, and means responsive to the voltage on said condenser to interrupt the X-ray tube transformer circuit in the event that the number of cycles of operation pre-selected is exceeded by one complete cycle.

10. An X-ray tube transformer coupled With an X-ray tube and in combination with a synchronizing control for said transformer comprising a pair of leading and lagging thyratrons, an initiating thyratron for initiating operation of the leading thyratron, a pair of interlocking thyratrons for alternately controlling the discharge of the leading and lagging thyratrons and a terminating thym ratron for terminating the operation of the interlocking thyratrons.

References Cited in the le of this patent UNITED STATES PATENTS 2,316,566 Constable et al Apr. 13, 1943 2,339,902 Akers et al. Jan. 25, 1944 2,473,237 Bivens June 14, 1949 2,473,238 Bivens June 14, 1949 2,486,089 Zavales Oct. 25, 1949 2,501,358 Stadum Mar. 21, 1950 2,512,193 Zavales .Tune 20, 1950 v2,573,029 Kuhlman Oct. 30, 1951 2,584,007 Fischer Ian. 29, 1952