US2583095A - X-ray tube safety device - Google Patents

Description

1952 E. R. GOLDFIELD ETAL 2,583,095

X-RAY TUBE SAFETY DEVICE Filed Nov. 2. 1948 2 SHEETS-SHEET 1 7 6 4o\| kw k7: km 73 E E K FIGEZ INVENTORS EDWIN R. GOLDFIELD & JACK BALL ATTORNEYS 1952 E. R. GOLDFIELD ETAL 2,583,0 5

X-RAY TUBE SAFETY DEVICE 2 SHEETS-SHEET 2 Filed Nov. 2, 1948 FIG.- 3

INVENTORS EDWIN R. GOLDFIELD & JACK BALL BY w, W, flaflwufi AT TOR N EYS Patented Jan. 22, 1952 U NI TED E S OFFIIEEJ 2,583,095 xnir ruBE. S ETY DEVIC Edwin- R. Goldfieid, University Heights, and Jack Ball, Cleveland Ghio, assignors to. The Picket X=B r Qqrmration W liienufacturin Di s qn nc C evel nd Obie. a corporation or Original application July 20, 1946, Serial No. 685,095: Divided: and this: application'- Novena her: 2, 1948, S erial No. 57,988

claim (or. 25045);

posure combined with an sexcessive kilovoltage @Dplied to the tubes.

Another object ofthe present invention is to prevent an excessive combination of time of exposure plus the milliamperage load on the tubes.

Still another object of the invention is to provide any excessive combination of time, kilo-.

voltage, or milliamperage; so as to overload the tube to the point of injury.

Another object of the present invention is to provide control means preventing overload ing of theX-ray tube by an excessive combination of kilovoltage together with a second; control factor which includes the. product of; the. millie amperage load on the X-ray tube times the number of seconds the tube is energized.

Another object of thepresent invention is to r e the X- a 1 1 a ain t. over d g it a series of exposures. repeated at short time intervals, no one of which issu fificient in itself, to overload the tube, but the cumulative results of, which would cause overheating; oi the; X-ray tube anode and injury to; the tube ing a control factor instep withthe heat dis;

sipation factor of theX-ray tubeanodeLwe build;

up the control iactorat the same-rate as the heat accumulation facton of theX- ray, tube anode and thus utilize our; novel QQntrol means; to prevent the l t e v rloadins. menti n d above.

Other objects and; advantages: of, the present invention will be apparentirom the accompanying drawings and description, andthe, essential featur w lbes t. orth, he pp ndedi claims 7 In the drawings,

Fig. 1 is-a wiring-diagram showingmneiorm; of

ourdevice wherein the product of? the millie amperage load on the X-raytube; times; the

number of seconds the. loadisapplied isutilized in a control circuit;

Fig. 2 is a modification of'the circuits of'Figl for protecting the X-ray tube against waccurnu1a.,. tive effect of short exposures. repeated'w-ith only;

short time intervals between-them; while- B a nge- Fig-.= 3 isa modification of the cireuits;ofifie 2v and shows another means of: accomplishing. the same purpose.

A X-ray tube; will take a. definite maximum loading which is afunc-tion of themilliamperage, the kilovoltag e and the time, for a definite load limit. If any one, of ther-aboveiis; increased, then it is necessary to decrease, atlleastl one,v of the. other two factors.

in Fi 1 wehave. qwmanautortransinrmer. supplied with elecfinical energy from the air. cuit L1, L2. Suitable tapsconnect leads H and lfiwith the primary l 3a;of aihi h-tensiqn trans-- former l3. The secondary Lib; oi; trans= former is connectedby. suitable leads, with the X-ray tube IS in the usual manner. The. midportion of the secondary circuit of the. trans,- iormer is groundeda-sshown and ,a-correction for, the milliamperage loadon, the; tube is inserted at this point as will be: presently, described. An, exposure is initiated by closing; push button Hi to energize relay 22 which attracfisrelay arma ture 22a, completing the, high tension transformer circuitthroughtheencrmally closed ,arma; ture 25b of relay-25. Thesfilainentpi,Xflaytube, I6 is supplied, with current. from the; source L5, L through transformer 61.1. The; time control tube 26 i of theses-filled triode; type havin a hot or cold cathodez2fial'," a fplate 26b and a. control grid 26c. The-power supply foifithistube maysuit bl source-of; al ernating, or, rectie ned current supplied to,l ines l6 and I1 133 .51.11)? able means not shown... Line 18, from the. s urce it through relay 25 totplatelfih compl the. circuit for this tube.

In circuit with; the; control grid 2.50; is a cone denser 32 which is; short circuited through lines 39- and 40 and the, normally closedarmature 22b; of relay 22 when an exposureis n t initiated, This keeps; the condenser iiz;fully discharged un til a e p su eiis, sta ted-a Wh n nushr utton.

i8 is closed, rela ZZattracts armature-f22h and,

opens; the circuit: at; condenser: 32;. which then timing-the; exposure! In,. ci-rcu it:withr.the: voltage; pp y forr 6 and: term nin tbeotime; nterva sarrto;- charge cond nser 3hare control elements fonconipensating'ior changes in the kilovoltage applied to theghign tension-transformer- I3, another; compensation forthe milliamperae load on therX-ray tu andath rda compensation factor-which takes; into account: the time the X-rayload appliedz to the-$1153.";

The compensat1on:..iorrchangesz;inzkiloyoltaeez applied.tozt iexzrartubss ntludeztlieztransmrmer:.

3 62 which has a primary 62a connected by lines 63 and 64 across lines II and I2 which supply transformer [3. A variable resistor 65 is supplied to provide necessary adjustments. The secondary 62b of this transformer is in circuit with condenser 32 as will presently appear.

The compensation for changes in the milliamperage load on the Xray tube is supplied in the central secondary circuit of transformer l3 by means of transformer 66. The primary 66a of this transformer is connected by lines 61 and 68 in the central secondary circuit of transformer 13 through variable resistor 69. The secondary 66b of this transformer is in circuit with condenser 32. The circuit for charging condenser 32 includes a portion of line 39, variable resistor 10, line ll, transformer secondary 6212, line 12, transformer secondary 66b, line 13, a rectifier l4, and line 15. The rectifier 14 may be a dry disc type rectifier or. a tube so as to apply a positive charge to the condenser 32.

The rate of accumulation of the charge on condenser 32 and therefore on the control grid 260' of the trigger tube 26 is a function of the adjustable resistor "Ill. This resistor introduces the time element in the control circuit. Thus, with a given resistor setting at ID, the higher the milliamperage which flows through the X-ray tube, the sooner condenser 32 becomes charged up to the critical value of the trigger tube 23, so as to cause the tube to fire completing the circuit from cathode 26a to plate 28b to energize relay which thereupon attracts the armature 25b and opens the circuit to transformer 13 so as to stop the exposure.

In similar manner, if the kilovoltage supplied through transformer l3 to the X-ray tube should be increased, this also would increase the speed of charging of condenser 32 through the control effect of the transformer winding 62b. This also would cause the tube 26 to fire sooner so as to stop the exposure.

According to the type or focal spot of the X-ray tube it the value or setting of the resistor T0 may be adjusted. If an X-ray tube permitting heavier loading capacity is used, then the value of it! may be increased so as to allow a greater milliampere-seconds limit. Thus, through the combination of the transformer winding 66b and resistor ill in the control circuit, one may limit the product of milliamperes times seconds that may be applied to the X-ray tube.

Referring now to Figs. 2 and 3, these circuits provide protection of the X-ray tube against exposures closely following one another and no one of which is suificient in itself to overload the X-ray tube. It is a fact that the ratings of X-ray tubes are based on a cold anode and if there is insufiicient time between successive exposures to cool the anode, then heat is built up in the anode faster than it can be dissipated and the tube may be overloaded. The circuits of Fig. 2 are exactly like those of Fig. l, with one exception presently to be noted. The lines 13, l8, '86, ll, 33 and 40 are intended to be joined to exactly the same lines of Fig. 1 along the dot-dash line A there indicated, and all of the diagram above the dot-dash line of Fig. 1 is hereby incorporated in Fig. 2.

The change in Fig. 2 consists in the inclusion of a resistance 13 in the circuit including line 33, condenser 32, line as and the armature 22b of relay 22. Thus, when no exposure is in progress. the armature 22b does not short-circuit the condenser 32. Insteadthe bleeder resistance 19 is in disconnectable shunt circuit across the condenser 32. Then, when an exposure is shut off, the armature 22b closes the circuit between lines 33 and 40 and the condenser 32 discharges through the resistance 79. This resistance is selected according to the type of X-ray tube used. The value of resistance 19 is made such that the rate of discharge of condenser 32 is equal to the rate of heat dissipation from the anode of the X-ray tube Hi.

It results from the above construction that if a second exposure is put on the X-ray tube immediately after the first one, the energy applied to the X-ray tube and the heat applied to the anode thereof keeps on increasing, and if both of these exposures were allowed to run the maximum safe value for a single exposure, the X-ray tube might be overloaded. However, since the resistance 19 discharges condenser 32 at a rate equivalent to the heat dissipation from the anode of X-ray tube 15, the condenser 32 will not be completely discharged at the start of the second exposure. Thus, it will not be possible to put a maximum exposure equivalent to that of the first exposure on the X-ray tube because condenser 32 will reach a voltage sufiicient to fire tube 26' quicker than in the case of the first exposure. In other words, it will only be possible to put on a second exposure corresponding to the amount of energy that was dissipated through resistance 19 between the first and second exposures. This makes it impossible to overload the X-ray tube by an accumulation of individual exposures quickly, one after the other.

In Fig. 3 we have shown a modification of Fig. 2 wherein tube 85 is substituted for the resistance l9, and the rate of energy dissipation from the condenser 32 is controlled by varying the charge on the control grid 800 by suitable means. Since nearly all of the parts and circuits shown in Fig. 3 are like those shown in Figs. 1 and 2, all parts and circuits performing exactly the same function are given the same reference characters. Only two changes are indicated in Fig. 3 as follows.

From a suitable source L3, L4, which might be either alternating current or rectified current but in the present instance rectified current is intended, line 81 connects the source L3 through armature 220 of relay 22 with line 82, relay 25 and line 83 to plate 26b. Since in this instance rectified current has been indicated at the sources L3, L4, once tube 26' has fired, it will remain locked out until the voltage is removed from the tube. In order to accomplish this, the lines 81, 82 are connected through the armature 220 of relay 22. Thus, after an exposure has been completed, button It is released and armature 22c returns to its normally open position indicated in Fig. 3, which opens the circuit to the plate 26b of tube 26' to restore control to the grid 260. It will be understood by those skilled in this art that if the source L3, L4 were alternating current, then the connection through the armature 220 would be unnecessary and lines 8| and 82 might be short-circuited, as indicated by the dot-dash line 86 of Fig. 3. This improvement might be readily incorporated in Fig. 1 if the source 16, 1! represented a rectified current, and changes in other diagrams involving trigger tubes might be provided with this modification to reset the trigger tube, if desired, as will be readily understood by those skilled in this art.

The second change in Fig. 3 involves the substitutionoftube for the resistance 19 of Fig. 2,

as mentioned above. It will be noted that condenser 32 is in circuit with lines 39 and 40 and the armature 22b of relay 22, as beforejwith the exception that tube 80 is now placed in this circuit replacing resistance 19 of Fig. 2. The cathode 8Ua of this tube may be of either the hot or cold type. The rate of bleeding off the charge from condenser 32 is controlled by proper selection of the charge on control grid 800. In the present instance, shunt resistor 84 connected across the source L3, L4 is tapped by line 85 to supply the selected voltage to grid 800.

The operation of Fig. 3 should now be apparent. When a first exposure is terminated, the

. condenser 32 is not short-circuited, but instead, is

connected through lines 39 and 40 and armature 22b with tube 80. The selection of the voltage on grid 30c makes the rate of discharge of condenser 32 equivalent to the rate of heat dissipation from the anode of X-ray tube l6. Here, therefore, as in the case of Fig. 2, a second exposure cannot run for as long a time as the first one unless the time interval between exposures is sufficient to completely discharge condenser 32 which means that the anode of the X-ray tube has had time to become cold.

In Figs. 1 and 3, we have shown the auto transformer It! with energizing circuit L1, L2, and a self-rectified unit. However, those skilled in this art will recognize that in most cases the type of X-ray unit used would be provided with a fourvalve-bridge-circuit. Our invention may be used,

however, using either a self-rectified circuit, av

half-wave rectified circuit, or a full-wave rectified bridge circuit, as will be readily understood.

This application is a division of our copending application Serial No. 685,095 filed July 20, 1946, now Patent 'No. 2,572,258 for X-Ray Tube Safety Device. I

What we claim is:

1. In the combination of an X-ray tube having 'a high-tension tube energizing circuit including a high-tension transformer having primary and secondary windings and including a filament energizing circuit having a filament transformer with primary and secondary windings, means controlling energization of said X-ray tube including a space discharge tube having control electrode means, a first control transformer having a primary winding in circuit with said hightension transformer primary winding, a second control transformer having a primary winding responsive to the anode current in said X-ray tube,

a capacitance in circuit with said control electrode, and a circuit for charging said capacitance including the secondary winding of each of said control transformers and a resistor selected according to the type and focal spot of said X-ray tube.

2. In the combination of an X-ray tube having a-high-tension tube energizing circuit. including means for selecting a desired voltage and a filament energizing circuit, means controlling energization of said X-ray tube including'a space discharge tube having a control electrode, a capacitance in circuit with said control electrode, and a circuit for charging said capacitance including means responsive to changes in said high-tension circuit independent of said voltage selecting means and means responsive to changes in said filament energizing circuit and a resistor selected according to the type and focal spot of said X-ray tube, said means responsive to changes in said high-tension circuit including a transformer having one winding connected in parallel with said high-tension tube energizing circuit and said transformer having a second winding in said capacitance charging circuit.

3. In the combination of an X-ray tube having a high-tension tube energizing circuit including means for selecting a desired voltage and a filament energizing circuit, means controlling energization of said X-ray tube including a space discharge tube having a control electrode, a capacitance in circuit with said control electrode, and a circuit for charging said capacitance including means responsive to changes in said hightension circuit independent of said voltage selecting means and means responsive to changes in said filament energizing circuit and a resistor selected according to the type and focal spot of said X-ray tube, said means responsive to changes in said filament energizing circuit comprising a transformer having one windin connected in the central grounded circuit of said high-tension tube energizing circuit and said transformer having a second Winding in said capacitance charging circuit.

4. In combination, an X-ray tube having an anode, electrical operating circuits for said tube, means for timing a period of energization of said tube including an electrical condenser effective to terminate said timing period upon a predetermined accumulation of charge, switch means for connecting said condenser for an accumulation of charge simultaneously with energization of said tube, a bleeder resistance in disconnectable shunt circuit with said condenser for discharging the charge from said condenser substantially coordinated with the rate of dissipation of heat from said anode, and switch means for connecting said resistance in circuit with said condenser during deenergization only of said tube.

5. In combination, an X-ray tube having an anode, electrical operating circuits for said tube, means for timing a period of energization of said tube including an electrical condenser effective to terminate said timing period upon a predetermined acoumulation of charge, switch means for connecting said condenser for an accumulation of charge simultaneously with energization of said tube, a space discharge tube in disconnectable shunt circuit with said condenser for discharging the charge from said condenser and having a control electrode, energization means for energizing said control electrode so that discharge of said condenser is substantially coordinated with the rate of dissipation of heat from said anode, and switch ineans for connecting said space discharge tube in circuit with said condenser during deenergization only of said first-named X-ray tube.

EDWIN R. GOLDFIELD. JACK BALL.

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

UNITED STATES PATENTS Number Name Date 2,058,992 Kearsley Oct. 27, 1936 2,295,297 Schneider Sept. 8, 1942 2,353,979 Weisglass July 18, 1944 2,404,905 Garretson July 30, 1946 2,448,371 Hiehle Aug. 31, 1948

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