US2561085A - Automatic exposure timer - Google Patents

Description

J 17, 1951 c. T. zAvALEs ET AL v 2,561,085

AUTOMATIC EXPOSURE TIMER Filed June 1, 1946 J .10 y 91 {i .1 9

I 63 U JU I W 54 ii A PI EUlEr? BY J E #15727.

ATTORNEY INVENTdRS I A412 I Patented July 17, 1951 AUTOMATIC EXPOSURE TIMER Gharles 'll. Zavales, New York, N. Y., Fred J. Euler, Jza, Baltimore, Md., and John E. Kalstein, Washington, I). 0., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 1, 1946, Serial No. 673,748

12 Claims. (Cl. 25l)-95) The present invention relates to what is known in the art as a phototimer which is used primarily with photo-fluoroscopic apparatus.

This latter apparatus is now quite extensively employed by the roentgenologist where it is desired to radiographically examine a large group of persons or objects in a short period of time. Instead of taking direct individual radiographic exposures with the time required to change films, the X-rays are passed through the object being radiographed on to a fluorescent screen, as in normal fluoroscopy. A photographic exposure utiliz ing continuous motion picture film is then made of the image cast on the fluorescent screen thus making a permanent record of the object, to be followed by another with a minimum lapse of time.

Inasmuch as the objects vary in thickness, the quality of the photographic exposure depends on the intensity of the fluoroscopic image appearing on the screen, with the latter in turn being determined by the kilovoltage, milliamperage, and time of energization of the X-ray tube. For the purpose of assuring reasonable uniformity in resultant photographs the phototimer was developed which operates to de-energize the X- ray tube when the image appearing on the fluorescent screen has reached a predetermined intensity.

Certain inherent disadvantages are, however, found in prior art phototimers. For example, when the image appearing on the fluorescent screen reaches the desired intensity, there is a certain time delay before the system responds and de-energizes the X-ray tube, which frequently has heretofore resulted in over-exposure Of the photographic film with attendant loss in diagnostic value. In addition, prior art phototimers have made no provision to protect the X-ray tube nor other costly parts of the system in the event that it fails to function in its normal intended manner. Moreover, with prior art phototimers there has been no way of ascertaining whether or not there is a failure of a given exposure and the latter could not be determined until after development of the film.

It is accordingly an object of the present invention to provide a phototimer wherein the X- ray tube is de-energized without any substantial time delay upon the photographic image reaching the desired intensity.

Another object of the present invention is the provision of a phototimer wherein protective devices are provided to prevent damage or destruction to the X-ray tube and other elements in the event of failure of operation of the phototimer for various reasons.

Another object of the present invention is the provision of a phototimer wherein an indication is provided for the purpose of signalling to the operator the failure of a given exposure.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein the single figure is a schematic illustration of a phototimer constructed in accordance with the present invention.

Referring now to the drawing in detail, the phototimer of the present invention comprises-a rectifier power supply chassis shown within the dashed frame 5, a photo-camera chassis shown within the dashed frame 6, and the X-ray tube excitation circuit illustrated to the right of the dashed frames 5 and 6. The photo-camera chassis 6 fastens to a photofluorographic hood 1, provided with a fluorescent screen 8, against which a patient or object 9 rests, and at the converging end of the hood a 35 or 70 milliammeter camera H] is secured, in the manner shown in the upper left hand portion of the drawing. Due to the position of the photo-camera chassis, light from the fluorescent screen 8 is directed by a lens [2, provided in the wall of a casing I3, on to the photosensitive cathode l4 of a multiplier phototube l5.

Referring now to the various elements contained within the photo-camera chassis 6, it will be noted that the cathode M of the phototube [5 connects to a terminal IE on the chassis 8, while its output anode I1 is connected by means of a manually operable switch I8, a fixed resistance l9, and contacts 28 of a relay 22, to another terminal 23 on the photo-camera chassis 6. Also, within the chassis E is a photofluoroscopic timing condenser 24 connected across the contacts 20 of relay 22, as well as a radiographic timing condenser 25 connected across additional contacts 26 of relay 22 for a purpose hereinafter described.

The multiplier phototube I5 is of the well known type and since its various multiplying -dynodes are supplied with a difierence of potential of increasing magnitude therebetween, a high resistance 2'! is connected, by a manually operable switch 28, a doubly variable resistance 29 for initial calibration and density control" and fixed resistance 30 across the chassis terminal I6 and 23, with the various multiplying electrodes tapped to points on the resistance 21. A

' glow relay tube 32 is also housed within the capacitor 26.

3 photo-camera chassis 6 which has one of its main electrodes connected to one side of the photofiuoroscopic timing condenser 24 while its starting electrode is connected through a fixed resistance 33, switch l8, and fixed resistance l9, to the opposite plate of condenser 26. The re maining main electrode of the glow relay tube 32 is connected to a chassis terminal 35 and in a similar manner the winding of relay 22 is connected to a pair of chassis terminals 35 and .35.

The advantage of housing all'of the above mentioned elements within the photo-camera chassis 8 resides in the fact that leakage'losses are minimized and high capacitance due to a long multiple conductor cable is reduced. Thus only a five conductor cable, all of which carry only control current, is required between the photo-camera chassis 6 and the rectifier power supply chassis and all conductors carrying low values of current for operation of the photo-tube l5 and glow relay tube 32 are ofrelatively short length.

Referring 'now' more particularly to "the :rectifier power supply chassis 5, it'will be notedthat the latter houses a transformer 40, the'primary Winding 42 of which is connected,v by means of conductors 43 and M and avariable resistancedfi of'about 1000 ohms, to taps of an rauto transformer 45 forming part of t -e X-ray tube energizingflunit, so that the primary'windingrM immediately energized upon closure of the vmain line switch (not shown) normally employing to connectthe'auto-transformer to azsource ofthe customary commercial supply of 195 to 250'volts. The-high voltage secondary'winding l'l of-trans 'former '40 is arranged to supply approximately 1150 volts D. C. which constitutes the input source for the photo-camerachassis 5.:

To this end oneside of the secondary winding -4'l'is connected, by a conductor 48, to a rectifier chassis terminal 48 and photo-camera terminal [6, and'from the latter to the cathode of photo tube I5, so that when conducting the: path will be completed from the anode ll, through switch it and resistance 19, to one plate of timing The opposite end of. secondary winding 4'! is connected to the anode of ahalfwave rectifying valve tube 50, with the thermionic cathode of the latter being connected, by a common conductor 52 to a rectifier chassistter- -minal 53; thence to photo-camera chassis terminal '23 and thus to the remaining plate of timing capacitor 24, and being grounded at G.

Itwill be noted that'the primary winding 42 of high voltage transformer 40 is shunted by a grid glow tube 54 having its main electrodes connectedito the respective line conductors :33 and. M through variable'resistance. 45, while its control electrodeis connected through a resistanceiifi of approximately 20,000 ohms to the line conductor '43.: This tube 54 operates as a' voltagestabilizer and passesicurrent during the portion of the altern'ating current cycle that the half-wave rectifier tube 50 is also conducting, the primary winding 32. being properly phased forthis purpose.

Thus in passing current :the control electrode of tube is momentarily positive with respect to the cathode and current flow between the main electrodes causes a voltage drop in the'resistance '45.

As the input line voltage varies, the amount of current taken by the tube 55 in shunt with the primary winding 42 -likewise varies. When the voltage increases the current through tube 5t varies and causes an' additional voltage drop in the resistance 45whichthus absorbs the effect of line voltage fluctuations resulting in the voltage stantially constant. The higher ohmic resistance 55 is employed to limit the flow of grid current during each impulse which results in more stable operation .of thetube 54.

Accordingly, since the-transformer 40- is energized by a constant voltage, the secondary winding 41 will charge the timing capacitor 24 at a uniform. rate in direct proportion to the light falling or phototube l5, once the normally grounded condition, of the anode of phototube l5 isremoved. by'opening of the contacts 20 and 2t of relay 22. This results from the fact that one or the other of the variable resistances 29 is selectively in circuit, depending upon the position of switch 28. The amount of resistance set at 29 determines the voltage biasing the ninth dynode of multiplier phototube I5 with respect to the eighth dynode, thus controlling the gain of the multiplier phototube :and'so the exposure density.

It will also be noted thatthe variable resist ance 29 forms;:part:ofxthe dividernetwork; com prising resistances 21, 29 and :3 0, across the :high voltage supply transformer. 40, tube 50, andthe low voltage cathode :heating source for tube. 50, Consequentlyya change in the resistance 29 will vary the voltage between the eighth and ninth dynodesof the multiplier :phototube I5 whereas such change in the resistance I 29 "will. have little effect :on the vvoltaget'across: these other elements; A filtering 2 capacitor 56: is; connected; across the rectified high voltage fromsecondary winding 5 41 resulting: in a. voltagelof .approximatelylZOO volts between the chassis terminals. l6 and" 49 to ground.

For the purpose of interrupting the X-rayv tube energizing circuit whenithe :image "appearing on the fluorescent screen 8' has reached the desired intensity, as'well as'to'protect the -X-ray tube-:in

the event-of failure of the phototimer and'togive asignal of such failure, the rectifierchassis; F2 housesvarious elementsamong whichris an addie -tional transformer 51 having'its primary winding 5:3 connected to the conductors 43, and 44 and 'thustotaps on the auto-transformer 46, inv the samemanner as primarywinding d2 of high ternv tor 52'. Adjustment of resistancei2 causes large variations in the value of the high voltage supply and allows'for'calibrating'the equipment for constant densities with large-variations in multiplier phototube outputs.

A similar low tension winding 03 also supplies heating energy to the thermioniccathode ofiullwave rectifier :52. AD. C. relay-irlhas onev end of its Winding connected by a conductor 65 to the cathode of rectifier while its remaining endiis connectedthrough a'resistance 56 of 35,000 ohms to common conductor-Maud thusto the midpoint of secondarywinding 59 from which the relay is energized Whenever transformer 57 and rectifier tube 60' are energized and functioning properly; On the other hand, shouldth'elow voltage power supply (1. e., tube 60 and transformer 51) fail for any reason,-relay 64 will not windings 59 and 63 of transformer 51, and tube 60, to more nearly approximate a direct current. A relay is provided with a pair of normally closed contacts 12 which in the de-energized po sition of the relay connects one plate of a safety timing condenser 13 through an adjustable re sistance 14 and thence by a conductor 15, con tacts 12, and a conductor 16, to common conductor 52, while the remaining plate of condenser 13 is directly connected to common conductor 52. This accordingly causes condenser 13 to discharge through resistance 14 each time the relay 10 is de-energized thus resetting the safety timer to an initial state of practically no charge at the inception of each exposure.

Relay 10 is provided with a pair of normally open contacts 11, one of which is connected by a conductor 18 to a point between tube 61 and resistance 68 and it will be noted that conductor I5 also connects to one end of the winding of a relay 19 and to one end of the winding of a further relay 80. The relay 19 is provided with a pair of normally closed contacts 82 and a pair of normally open contacts 83, while the relay 80 has a single pair of normally closed contacts 04.

As shown, the X-ray tube excitation circuit is controlled by a pair of relays 85 and 93, with the relay 85 provided with a pair of normally open contacts 01 and the relay 96 having a pair of normally open contacts 68 and 89. Since one end of the primary winding 90 of a high tension transformer 9I is connected directly to a tap of the auto-transformer 46, closure of contacts 89 of relay 86 will connect the remaining end of primary winding 90 to a further voltage tap on the auto-transformer 43 through a resistance 92. The simultaneous closure of contacts 83 of relay '86 completes an energizing circuit to the Winding of relay 85, as hereinafter explained, which causes closure of its contacts 81 thus short-circuiting the major portion of the resistance 92, employed merely to absorb the sudden rush of current due to relay 86 operating slightly prior to that of relay 85.

Upon energization of the primary winding 90 of transformer 9|, the secondary winding 93 thereof supplies unidirectional energy to the X- ray tube 94 through a high voltage rectifier bridge arrangement 95 with the current being measured on a milliammeter 96 connected to a rectifier bridge circuit 91 in well known manner.

The contacts of the various relays, as above noted, are employed to operate control circuits. Although all of the relays, with the exception of relays 54, 19 and 80, are energized from an alternating current source, for the sake of simplicity in describing the control circuits, it will be assumed that at a given moment the A. C. supply source has a positive and negative polarity. Ac-

. 6 cordingly, supply conductor 43 will be assumed as the negative and conductor 44 as positive.

As shown conductor 43 extends to normally open contacts 98 of D. C. relay 64, so that upon closure thereof a negative polarity will be supplied by a conductor 99 to one end of the winding of relay 10. Since a conductor I00 is connected to conductor 43 and extends to one side of a signal alarm I92, such as a bell, buzzer, lamp or the like, and a conductor I03 is also connected to the conductor 99 and extends, through a rectifier chassis terminal I04 and photo-camera chassis terminal 36, to one end of the winding of relay 22, a negative polarity is thus supplied to the windings of both relays 22 and 10 upon closure of relay contacts 98 while the signal alarm I02 receives a negative polarity independent of contacts 98. A negative polarity is also supplied from the supply conductor 43 directly to the windings of relays 85 and 96 by a conductor I05.

The positive conductor 44 is connected to the exposure switch I06 which upon closure extends this positive polarity through a conductor I01 to a junction I08. From the latter a conductor I09 extends to a rectifier chassis terminal II 0 and photo-camera chassis 35 and thus to the other end of the winding of relay 22 and since a conductor H2 connects to the conductor I09 and to the other end of the winding of relay 10, a positive polarity is thus supplied toboth relays 22 and 10, upon closure of exposure switch I00. Also extending from the junction I08 is a conductor H3 which connects to one of a further pair of normally open contacts H4 provided on relay 10. From the other contact of this pair II4 a conductor II5 extends to the normally closed contacts 84 of relay 80, and through such contacts 84, by means of a conductor II6, to the normally closed contacts 82 of relay 19, thence by a conductor II1 to the other end of the winding of relay 86. Thus the energization of this latter relay 8B, which initiates an X-ray exposure, is dependent upon the closure of exposure switch I06 and also closure of contacts II4 of relay 10. A conductor II8 connects the other side of the signal alarm I02 to one of the normally open contacts 83 of relay 19.

It will be noted that the other end of the winding of D. C. relay is connected by a conductor I I9 to a rectifier chassis terminal I20 and thus to photo-camera chassis terminal 34 and. the remaining end of the winding of relay 19 is connected to one of the main electrodes of a glow relay tube I22 with the other main electrode of this tube being connected to common D. C. supply conductor 52. The safety timing condenser 13 is also connected through a resistance I23 of about 10,000 ohms to the control electrode of the glow relay tube I22.

The operation of the photo-timer of the present invention is as follows: the main line switch (not shown) is first closed thus energizing the autotransformer 49. The latter in turn energizes the primary windings 42 and 58' of' the respective transformers 40 and 51 with the former being supplied with a substantially constant voltage by operation of voltage regulator tube 54 in the manner previously described. Energization of transformer 42 causes the secondary winding 41 thereof to charge filtering capacitor 56 and supply current for the divider network comprising the resistances 21, 29 and 30 at this time, since the phototube I5 is non-conductive as nolightlis falling on its cathode, due to the fact the X- ray 71 tub'c'94: is not. yet energizing and hence no image appears on .the fluorescent screen 8.

However, energization of transformer causes its? low tension windings SI and 53, to heat the thermionic; cathodes of the respective rectifier tubes59 and E9 and the secondary winding 59 to.-energize the winding of relay 94, through a circuit extending from the mid-point of transformer 59 through negative or common conductor 52, resistance 66, to winding of relay 94 and hence through conductor 65. and rectifier tube 69 to one or the other ends of secondary winding 59 during alternate half-waves of the alternating current cycle. At the same time capacitortQ is charged by secondary winding 99.

The winding of D. C. relay 64 thus becomes energizedimmediately upon. the filament of rectifier tube 69 reaching electron. emitting tempera.- ture and closes its normally open contacts 98.

Closure of the latter merely conditions the control circuits for. operation since no circuits are completed by contacts 98 but negative polarity 'fromtheconductor 43 is supplied to one end of thewindings of relays 22 and I9, by the conductors 99, and I93. Also negative polarity issupplied directly to one side of the signal alarm I92by conductor I00.

The doubly variable resistance 29 in the photocamera, chassis having been set for, the desired calibration and density of film, a patient or object 9 is positioned in front of the fluorescent screen 8 carried at the front of the camera-hood, readyfor. an exposure. The operator then closes the exposure switch I96. This completesa circuit from positive supply conductor 44 through conductor I91, junction I93, and conductors I99 and-I I2, terminals H9 and 35, to the other end of "the windings of both relays 22 and i9, and thence through conductors 99 and I93 and the now closed'contacts 98 of relay 54 back to negative supply conductor 43. Energization of relay 'III' opens the discharge circuit for safety timing condenser I3 at the contacts 52 and causes closure of'its normally open contacts I1 and H4. Closure ofcontacts II4 completes a circuit from the junction I08, through conductor II3, now closed contacts H4, conductor II5, normally closed'contacts 84 of relay 99, conductor III normally closed contacts 82 of relay I9, conductor In to. winding of relay 89 and back to line conductor'43 through conductor I95.

The relay '89 is thus energized and closes its normally open contacts 88 and 89. Closure of contacts: 89 according energizes high tension transiormers9I throughresistance 92, and closure of contacts 88 energizes the winding of relay 85 withattendant'closure of itsnormally open contacts3'i, which short circuits the major portion ofyresistance 92 after but an instant following operation of relay 86. The X-ray tube 94 accordingly is energized, and generates X-rays which are directed toward the-object 9.

The-, energization of relay 22 simultaneously withrelayll], as above noted, causes the normally closed contacts and 26 of relay 22 to open thus removingthe grounded condition of timing capacitors 24 and 25. The closure of normally open contacts 11 of relay I9 connects the.conductor "I8 to the conductor 15 which thus supplies a: positive side of the control voltage from .the transformer 59 to one end of each of the-windings of relays I9 and 89, but since the negative side-is at this time interrupted neither ofi theselatter relays are-as yet energized.

Upon .theappearance of an image on the fluo- 8. rescent-screen 8, due-to the passageof Xerays from the now energizedX-ray tube 94, the light from such image passes through the lens I2- and falls upon the cathode I4 of phototube I5. Since transformer 49 was previouslyenergizedupon closure of the main line switch, the-secondary winding 41 thereof now charges timing capacitor 24 at a rate directly proportional to the light falling on the phototube I5, througha circuit extending from one end ofv secondary winding 41, through conductor 48 and chassis terminals 49 and IE, to the cathode I4 of phototube I5. From the anode H the circuit then extends through switch I8, resistance I9 to one side of capacitor 24 and thence from the other plate thereof, through chassis terminals 23 and 53, negative or common conductor52 and rectifier tube 50, to theotherend of secondary winding 41.

When capacitor 24 has become charged to a value equal to the triggering voltage of the glow relay tube 32 at a rate dependent upon the light falling upon the phototube I5 the voltage thereof is impressed through current limiting resistance 33 across one of the main electrodes and the control electrodeof glow relay tube 32. As is. characteristic of this type tube, a discharge occurs between thelatter two electrodes when the triggering voltage is reached which ionizes the gas within the tube causing a discharge to occur between the two main electrodes. Breakdown of this tube32 accordingly completes a circuit extending from the mid-point of secondary wind ing 59, through negative or common conductor 52, chassis terminals 53 and 23, tube 32, chassis terminals 34 and I29, conductor H9, winding of D. C. relay 89, conductor I5, now closed contacts H of relay I9, conductor I8, resistance 98, and conductor 65 through rectifier tube til back to one or the other ends of secondary winding 59.

Relay 89 is accordingly energized by the unidirectional energy from winding 59 and opens its normally closed contacts 84. Opening of these latter contacts 84 thus interrupts the control circuit causing de-energization of relays i9, 85 and 86 with a cessation in the generation of X-rays from the X-ray tube 94 due to opening of relay contacts 81, 88 and 89. Release of the exposure switch I96 allows opening of contacts TI of relay III to interrupt the D. C. source of supply for relay allowing it to again close its normally closed contacts to condition the control circuit for making another photo-fluorograph upon closure-of the exposure switch I06. At the same time closure of the normally closed contacts I2 of relay I9- again connects the safety timing condenser I3 in series with the resistance 14 allowing the condenser I3 to completely discharge, thereby resetting the safety timer.

It can accordingly be seen that upon the timing condenser 24 becoming completely'charged at a rate dependent upon the light falling on the multiplier phototube I5 and under control of the doubly variable resistance 29, the X-ray tube 94 is immediately de-energized when the image appearing on the screen 8 is of the desired preselected density to assure a proper film exposure. Moreover, the resistance I9 in series with the timing condenser 24 functions as a compensating arrangement to allow for the X-ray on contactor drop-out time, namely relay 86 and its contacts 88 and 89. It has been found that this drop-out time is of the order of 1.2 cycles, and in order to prevent an over-exposure must be compensated for which is one of the salient features of the present invention.

As previously mentioned the current through phototube I varies in proportion to the intensity of the light emitted from the fluorescent screen 8 within the hood I. Thus the timing condenser 24 charges up to a given voltage in a time proportional to light intensity and reaches this given voltage when the same quantity of light has fallen upon the phototube cathode H. The condenser 24 accordingly reaches a voltage suflicient to trigger glow relay tube 32 and terminate the exposure when a given amount of light (controlled by density control resistance 29) is emitted by fluorescent screen 8. However, since the drop-out time for contacts 88 and 89 of relay 86 requires 1.2 cycles this additional time of energization of the X-ray tube 94 actually adds to the exposure before it is finally terminated. With a long exposure of .3 second (18 cycles), this additional 1.2 cycle exposure means only a 6.7% over-exposure which is short enough as to be disregarded since it produces no serious results to the film. However, on a short exposure of .05 second (3 cycles), which is within the range of a large percentage of exposures, this additional 1.2 cycles of relay drop-out time means a 40% over-exposure that is serious since it results in faulty films.

In order to produce films of a consistent density with varying exposure times, the compensating resistance I9 is utilized, since with the latter in circuit, the voltage drop across the compensating resistance varies directly with phototube output current, and the glow relay tube 32 triggers when a given total voltage is reached across the compensating resistance I9 and timing condenser 24. Accordingly, the condenser 24 needs to charge only to the difference of the given total triggering voltage necessary and the voltage appearing across the compensating resistance I9. Inasmuch as the voltage across the compensating resistance I9 varies inversely with the time of exposure, consistent film densities are obtained at varying exposure times.

In addition to the compensating arrangement the present invention provides a protective circuit which suppresses voltage surges and also protects the X-ray tube from injury by overloading or the like. As above noted, relay 54 and resistance 66 comprise a protective circuit which prevents operation of the apparatus should the low voltage power supply, consisting of transformer 5! and rectifier 60, fail for any reason. If this failure should occur during the making of an exposure it would be impossible for the timing tube 32 and the safety timing tube I22 to ionize and operate relays I9 or 80, either of which terminates the exposure. By placing relay l0, which initiates the exposure, under control of relay 64, the exposure is terminated upon failure of the low voltage power supply, even though relays I9 and 80 fail to operate because their respective control tubes I22 and 32 do not become conductive, and of course if the power supply has failed prior to the making of an exposure then relay 64 cannot initially operate.

Since transformer 5! has its primary winding 58 connected to the auto- transformer supply conductors 43 and 44, it is possible for the output potential from secondary winding 59- to vary and impress a varying anode potential on tubes 32 and I22 which eifects their ignition thus resulting in inconsistent timing. In order to stabilize the low voltage power supply, thevoltage regulator tube 8! and resistance 68 lsprovided,

10 so that if the output voltage of the low voltage power supply increases, the current taken by tube 61 increases. This increase in tube current causes an increase in the voltage drop in resistance 68 which subtracts from the output voltage of the low voltage power supply.

On the other hand, if the output voltage decreases, the current through tube 61 will likewise decrease and the voltage drop in resistance 68 will decrease thus adding to the output voltage of the low voltage power supply. Thus the voltage across tube 6? remains substantially constant and since the voltage for timing tube 32 and safety timing tube I22 is taken directly across tube ill, the ignition potential of tubes 32 and. I22 remains constant. The condenser 69, as before mentioned, is utilized to smooth out the pulsations so that the rectified low voltage power supply more closely approximates a true D. C. source.

The safety time circuit comprising condenser l3, variable resistance Ill and glow relay tube I22 together with fixed resistance I23 and relay I9 is provided to terminate an exposure after the lapse of a definite period of time in the event the timing circuit, which should operate in response to light falling on the phototube I5, fails for any reason to so operate. Upon operation of relay III, in the manner previously explained to initiate an exposure, safety-timing condenser 73 is charged during the same period that main timing condenser 24 is being charged through phototube I5.

This charging circuit extends from conductor It (now carrying a positive polarity from transformer 57 through conductor 65, resistance 68, conductor 78 and closed contacts ll of relay 18) through variable resistance I4 to condenser "13 and thence to the negative or common conductor 52. Resistance I4 is adjusted to regulate current fiow and thus the time required to charge condenser I3 which is made comparable to that normally required to charge main timing condenser 24 but so that the latter normally operates to terminate the exposure whereas safety timing condenser l3 operates to terminate the exposure only when a safe period of time elapses and condenser 24 fails to operate.

Upon condenser I3 becoming charged to the triggering potential of glow relay tube I22 the latter becomes conductive thus completing the circuit from negative or common conductor 52 through tube I22 to winding of relay I9 and thence to conductor I5 carrying a positive polarity from the lower voltage power supply source. This accordingly energizes relay I9, causing opening of its normally closed contacts 82 included in the X-ray exposure control circuit previously traced, and terminating the exposure in the same manner as contacts 84 of relay 80 would have terminated the exposure had this latter relay become energized since relay contacts 82 and 84 are in series.

This operation of relay I9 also closes normally open contacts as thus completing a circuit to the signal alarm I02 so long as the exposure switch I06 is closed which indicates to the operator that the safety timing circuit, or time limit, terminated the exposure, instead of the main timing or phototimer circuit. Such audible indicator advises the operator that either the X-ray tube or phototube has failed for some reason, or that the kilovoltage preset for the particular patient or object being radiographed,

ascri es wastoo low resulting in anexposure which .is longer than safe tube rating.

The present invention also provides for the -photo-timingof 14 in. X l1 in. radiographs with consistent film densities. In making radiographs a film cassette containing intensifyinglscreens within the filmcassette positioned on the hood l-infront of the fluorescent screen ii. A shutter m: provided in the hood 7 is rotated by a handle or crank iZfi from its-normally horizontal posi tion, as shown in full line, to a vertical position, as-shown in dotted lines, in front of the camera shutter. Although shown schematically in'the 'draw-in'gyrotation of this shutter to the vertical position also moves switches i8 and 23 within ti e photo-camera chassis from thei respective full line positions to that shown in dotted lines and, though not shown, the circuit to the camera motor is aleo interruptedsby movement of the shutter i2 3.

-l\'/lo*-. ementof switch i8 cuts timing condenser itand compensating resistance is outxof circuit anclwuts in timing condenser 25' and a' further series connectedcompensating resistance i282 In a similar manner switch 28'cnts out of circuit the dou-oly variable resistance ordensityccontrol 29 and cutsin assimilar density control doubly variable resistance: $2 3, which thus conditions the entire apparatus"for'operationto take a 14 x i7 'radiograph, inthesame manner .as previously 'describedr'forrthe malringof aphoto-fluorographic-exposure.

The necessity for a change in certain elements due to the;fact;that theintensifying screens withinthetfilmcassetteare. usually of a different typezof :fluorescent' screen than the screen 8 withinpthehood Leandhence the X-ray film receives light from a; differenttype screen than that from whicht tl1e..:phototube.'i5 receives light, namely, screenzil. Consequently, because ofthe response differences ofthe screens, film and phototu-be, it is; necessary toutilize av compensating resistance l25 =and timing condenser 2-5, as well-as adoubly variable-resistance i2'i,.ofa somewhat different orderiof magnitude than usedfor photofluoroisoopy. .However, lay-selectingthe proper value for thecombinationlof timing condenser 25 andcompensating resistance ifiEtandwith a desired setting of :the- .densitycontrol resistance till, 14 x i7? radiogra-p-hs'ofconsistentdensity are obtainable :With a single 2 a ray-tube. kilovoltage and milliamperage.fonvarious patient or obj ectthiclcnesses. When the shutter Hi l isreturned to its normally horizonalposition theapparatus is again set for photofiuorosoopy.

Itthus becomes obvious. to those skilled in the .arttthat aiphototimeriis herein provided which accurately andautomatically operates to terminate either a radiographicor photofiuorograpliic exposure to insure consistent film densities with patients of varying-thicknesses, or for varying exposure times. Also compensation is made for the time required'for various instruinentalities to operatetoterminate such exposure sothat the apparatus operates accurately .in response to trulyfdesired film density and not to any pseudodensity which includes operation time of other circuit elements. Moreover, the phototimer of the present invention incorporatesa protective arrangement preventing injury to the'X-ray tube andivoltage regulatingiof thevarious tubes to insure consistent operation under all conditions. Furthermore, an audible indicator is provided to advise the operator when "certain undesirable operating conditions of the apparatus exist.

Although onespecinc embodiment 'ofthe present invention has been showinsanddescribed, it is to be understood that vsti-ll furtherv modificae tions thereof maybemad-e without. departing from the spirit-and scope or the appendedclaimsr We claim:

1. A phototimer for automatically controlling energization of an X-ray tube toconsistently produce radiographio images of uniform-density regardless of variations'in object thicknesses or varying exposure times comprising energizing means for said X-ray tube, control means responsive to initiation by an operator adapted to auto matically cause operation ofsaid X-ray tube en ergizing means, protective'means including asubtantially constant voltage power supply and'a relay energizable therefrom and operable to partially complete a circuit to said-control means and serving in event of power supply failure to prevent operation-of said control means with otherwise attendantpossible injury to the X-ray tube, and intensity responsive means automati caily'operable tocaus'e cessation in the operation of said X-ray tube energizing means when the ra'diographic image produced bypassage of X- rays through an object onto a lightsensitive sure face reaches a predetermineddensity.

2. A phototimer for automatically controlling energization of an 'X ray tube to consistently produce radiographic images of uniform density regardless of variations in object thicknesses or varying exposure times comprising energizing means for said.X-ray'tube, control means responsive to initiation by anopera-tor adapted to automatically cause operation of said X-ray tube energizing means including a plurality of'relays whose contacts normally close'a partial circuit to said control means, protectivemeans including a substantially constant voltage power supply and a relay energizable therefrom and operable to partially complete a circuit to t-he'windings of the relays of said control means and serving in event of power supply failure to prevent operation of said control means with otherwiseattendant possible injury to'theX-ray tube, and intensity responsive means automatically operableto complete the partially completed circuit to the'windving of one of the relaysoi said control'means to render the latter effective to cause a cessation in the operation of saidX-ray tube energizing means when the radiographic image produced by passage of X-raysthrough an object on to alight sensitive surface reaches a predetermined density.

3. A .phototimer for automatically controlling energization of an 'X-ray tube to. consistently produce radiographic images of'uniform density regardless of variations'in object thicknesses'or varying exposure times comprising energizing means for said X-ray tube, control means respon sive toinitiation by an operator adapted to automatically cause operation of said X-ray tube energizingmeans, protectivemeans operable'to condition said control .means'for operation and 0perable' in event of power supplyfailure toprevent operation of said control means with otherwise attendantpossible injury to the IX.-ray' tube, intensity responsive means automatically operable to'causea cessation in the operation ofsaid X-ray tube. energizing means "when the 'radiographic image'produced by. passage 'ofiX-rays throughan object onto a light sensitive surface 'reachesa predetermined density, and compensating means connected" to said intensity-responsive meansand operable to 'con1pensate"for"'the time delay're quired for said X-raytube energizing means to cease operation in response to operation of said intensity responsive means to prevent an overexposure and assure density uniformity of the radiographic image.

4. A phototimer for automatically controlling energization of an X-ray tube to consistently produce radiographic images of uniform density regardless of variations in object thicknesses or varying exposure times comprising energizing means for said X-ray tube, control means responsive to initiation by an operator adapted to automaticallycause operation of said X-ray tube energizing means, intensity responsive means automatically operable to cause a cessation in the operation of said X-ray tube energizing means when the radiographic image produced by passage of X-rays through an object on to a light sensitive surface reaches a predetermined density, and safety timer means automatically operable to cause a cessation in the operation of said X-ray tube energizing means after the lapse of a preselected period of time in the event said intensity responsive means fails to operate and terminate the X-ray exposure.

5. A phototimer for-automatically controlling energization of an X-ray tube to consistently produce radiographic images of uniform density regardless of variations in object thicknesses or varying exposure times comprising energizing means for said X-ray tube, control means responsive to initiation by an operator adapted to automatically cause operation of said X-ray tube energizing means, intensity responsive means automatically operable to cause a cessation in the operation of said X-ray tube energizing means when the radiographic image produced by passage of X-rays through an object on to a light sensitive surface reaches a predetermined density, and safety timer means including a capacitor adapted to becharged over a preselected period of time simultaneously with operation of said intensity responsive means, and automatically operable to cause a cessation in the operation of said X-ray tube energizing means after the lapse of such preselected period of time in the event saidintensity responsive means fails to operate and terminate the X-ray exposure.

6., A phototimer for automatically controlling energization of an X-ray tube to consistently produce radiographic images of uniform density regardless of variations in object thicknesses or varying exposure times comprising energizing means for said X-ray tube, control means responsive to initiation by an operator adapted to automatically cause operation of said X-ray tube energizing means, intensity responsive means automatically operable to cause a cessation in the operation of said X-ray tube energizing means when th'e'radiographic image produced by passage of X -r'ays through an object on to a light sensitive. surface reaches a predetermined density, safety timer means automatically operable to caus a. cessation in the operation of said X-ray tube energizin means after the lapse of a preselected period of time in the event said intensity responsive means fails to operate and terminate the .X-ray exposure, and an indicator operable in. re sponse to operation of said safety timer means to apprise the operator that the safety timer means and not the intensity responsive means terminated the X-ray exposure.

7. A phototimer for automatically controlling energization of an X-ray tube to consistently produce radiographic images of uniform density regardless-of variations in object thicknesses or varying exposure times comprising energizing means for said X-ray tube, control means responsive to initiation by an operator adapted to automatically cause operation of said X-ray tube err-- tive surface reaches a predetermined density,-

safety timer means including a capacitor adapted to be charged over a preselected period of time simultaneously with operation of said intensity responsive means and automatically operable to cause a cessation in the operation of said X-r-ay tube energizing means after the lapse of such preselected period of time in the event said intensity responsive means fails to operate and ter minate the X-ray exposure, and an indicator operable in response to operation of said safety timer means to apprise the operator that the safety timer means and not the intensity responsive means terminated the exposure.

8. A phototimer for automatically controlling energization of an X-ray tube to consistently produce radiographic images of uniform density regardless of variations in object thicknesses or varying exposure times comprising energizing means for said X-ray tube, control means responsive to initiation by an operator adapted to auto-v matically cause operation of said X-ray tubeenergizing means, protective means operable to condition said control means for operation and serving in event of power supply failure to prevent operation of said control means with otherwise attendant possible injury to the X-ray tube, intensity responsive means automatically operable to'cause a cessation in the operation of said X-ra tube energizing means when the radiographic image produced by passage of X-rays through an object on to a light sensitive surface reaches a predetermined density, safety timer means automatically operable to cause a cessation in the operation of said X-ray tube energizing means after the lapse of a preselected period of time in the event said intensity responsive means fails to operate and terminate the X-ray exposure, and an indicator operable in response to operation of said safet timer means to apprise the operator that the safety timer means and not the intensit responsive means terminated the X-ray exposure.

9. A phototimer for automatically controlling energization of an X-ray tube to consistently produce radiographic images of uniform density regardless of variations in object thicknesses or varying exposure times comprising energizing means for said X-ray tube, control means responsive to initiation by an operator adapted to automatically cause operation or said X-ra tube ener-- izing means including a plurality of relays whose contacts normally close a partial circuit to said control means, protective means including a substantially constant voltage power supply and a relay energizable therefrom and operable to partially complete a circuit to the windings of the relays of said control means and serving in event of power supply failure to prevent operation of said control means with otherwise attendant possible injury to the X-ra tube, intensity respom sive means including a circuit having a capacitor therein adapted to be charged through a phOt0- electric cell at a rate directly proportional to the intensity of the light falling thereon from a radi0- accuses .graphicimage appearing nalight sensitive surface. ait-er passage. of .X-rays through-.any'object onlltoisaid surface, and automatically operable: to cause energization :of' one of therr'elaysof said controlmeans with :an attendant cessation-f the operation. of said 'X-rayitube energizing means whenlthexradiographic image reaches a predetermined density; safet timer means. automatically operable-to cause a cessation. in the operatiomof saidsXa-raytube energizing means after the -lapse f.iarpreselectedperiod of time-in the event said intensity responsive means. Liails .to soperate to terminate'the X-ray. exposure, and an. indicator operable inrresponse to the operation ofsaid safe-- ty timer;meansstoiapprisethe operator that the safety timer. means and not theintensity responsivesmeans. terminated the:X-ray exposure.

.10.. phototiiner; for. automatically controlling energizationof anvXi-ray tubeto. consiStentlyproduce; radiographic. images .of uniform density-regardless of variations in object thicknesses or varying exposure times comprising. energizing meansffor said:Xi-ray'tubegcontrol means responsive to initiation by an operator. adapted to automatically cause operation of said X-ray tube energizingmeans including a plurality or" relays Whose contacts normally closea partialcircuit to said. control means, protectivemeans. including .asubstantiall constant voltage power supplyand a-relay'ener-gizable therefrom and operable to partially complete a circuit to the windings of therrelays. of said control. means and serving in event :of power supply failure to prevent operation oisaid control-means with otherwise attendant possible injury to the X-ray'tube. intensity responsive means including .a circuit having :a capacitor therein adapted to be charged through aphotoelectric cell at a rate directly. proportional .to. the intensity of the light falling thereon from a'zradiographic image appearingonlaulight sensitive surface. after passage oBX-Qays through an object on. to. said surface, and automatically .opei ableto cause energization of one of the relays-of saidxcontrol means with anattendant cessation :offtheoperation of vsaid X-ray tube energizing means when the radiographic image. reaches a predetermined density; .an nnpedanceelement connected to said capacitorsubject to a voltage inversely variable with the timeaof energization of-said X-ray tube; and operable tocompensate U1 for the time delay required for said X.-ray tube energizing means to cease operationiin: response to operation of said intensity responsive means to prevent an over-exposure and assure .density uniformit of the radiographic image, safetytimer means automaticallyxoperable to cause a cessation in the operation of1 said X-ray tube energizing means after the lapse of apreselectedzperiod'of time: in the event said intensity responsive means fails: to operate to terminate the :Xera'y. exposure, andanfin'dicator operable in response. to theroperation of said safety timer meansto apprise the is operatonthatthezsafety timer meansandi notthe inten'sitytresponsiva means? terminated the. Ysray exposure.

1.11. 'Aiphototim'er'forsautomaticallyi controlling.

energization of an 'Xray tube to consistently produceradiographic: images of: uniform: density regardless: of variations-in object thicknesseseor varying exposure timesv comprising:alight-tight.

Xerays'. through anobject-on to said; fluorescent.

screen .or film reaches a predetermined sdensity; and. means for Shielding. said cameratduring. the making of a. radiograpnic :exposurei-on the lfilm Within said cassette. and operable uponmovement of; said means to change r the adjustmentaofsaid intensity responsive means.

-.12. A; phototimer' for.- automatically controlling energization ofan :X-ray tube to consistently-produceradiographic images of uniform density-regardless of variations inrobject. thicknesses or varyingexposure times comprising a-.light tight hoodprovided with. a fluorescent iscreen'. atsone end thereof and a camera at-its other end. for photographing images appearing on said fluorescent. screen, :means. forsu-pporting.aafilmlcar ryingrcassette at theend .of thehood.adjacent saidiluorescentscreen, energizing. meansfor-said X.-ray. tube, intensity responsivemeans automatically operable. to. cause. .a cessation in the operationv of. said: Xeray tube. energizinghmeans vwhen the. radiographic image. produced by passage. of X-rays throughan object onto saidfiuorescent screen or film reaches .a,.predetermined...density, and. a. shutter in= said hood movable into..a ;posi.- tion' to shield said. camera when. a radiographic exposure onmtheffilm withinsaid cassettaisidesiredI-andloperable to adjust thessettinghofhsaid intensity responsive means. as said J shutter. .is moved to its various positions.

- CHARLES LT. ZAVAEES'.

FRED J EULER,-.-JR;- J OHN: E. IKALSII'EIN;

REFERENCES CITED. 'Th'e'following references areofrecoid 'i-n -the file 15f this patent:

UNITED STATES "PATENTS Number Name Date 2,136,116 Mowry Nov. 8,..1938 :.2,252;530 "Sweenyet al. 'Aug..11-2 19.4'1 l2-,35 3;;980 Weisg-lass J uly, 1.18 1-944 2;.401289. 'Morgan :et 1 a1 May 28, 19.46v

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