US2541187A - Photoelectric timer for x-ray apparatus - Google Patents

Description

Feb. 13, 1951 J. BALL ET AL PHOTOELECTRIC TIMER FOR X-RAY APPARATUS Filed Nov. 13, 1947 TO X- RAY TRANSFOR MER (K 88- 5 880. s s

91b 92b INVENTORS JACK BALL & EDWARD B GRAVES 736% a flm AT TOR NEYS Patented Feb. 13, 1951 PHOTOELECTRIC TIMER FOR X-RAY APPARATUS Jack Ball, Cleveland, and Edward B. Graves,

South Euclid, Ohio, as

signorsto Picker X-Ray Corporation Waite Manufacturing Division, Inc., Cleveland, Ohio, a corporation of Ohio Application November 13, 1947, Serial No. 785,664

9 Claims.

This invention relates to improvements in a photoelectric timer for use in connection with X-ray apparatus for Roentgen photography.

The purpose and theory of the type of apparatus here disclosed is fully set forth in United States Patent No. 2,401,289, granted May 28, 1946, to Russell H. Morgan and Paul C. Hodges, to which reference may be had for an explanation of the theory. The present invention provides an improvement over the above mentioned 1 patent.

In the Morgan, Hodges patent and in the present application use is made of a phototube of the general type disclosed in United States Letters Patent No. 2,231,697, granted February .11, 1941,

to Vladimer K. Zworykin et al. In such a phototube there is provided a light sensitive cathode, an anode, and a series of multiplying electrodes called dynodes. Visible radiation produced on a fluorescent screen by an X-ray exposure fell upon the light sensitive cathode and, through the multiplying electrodes, resulted in an output which was utilized to charge a condenser. When a sufiicient charge accumulated on the condenser,

it tripped a trigger tube for terminating the X- ray exposure Morgan and Hodges used a Thyratron type control tube. Since this tube is a negative-control tube, they found it necessary, as set forth in the above mentioned Patent No. 2,401,289, to use the ninth 'dynode as a collector so as to obtain a charge of the right polarity to trip the trigger tube since the plate or anode of the phototube would give a negative charge as it is the receiver of electrons. This patented device cut down the sensitivity obtained. It is an object of the present invention to use the plate of the phototube for the tripping of the trigger tube so as to obtain greater sensitivity. 7

In an attempt to get better results Morgan and Hodges tried different types of trigger tubes and also tried an amplifier between the phototube and the trigger tube. Difficulties were still encountered because a negative potential was supplied on the control grid or starter anode of the trigger tube and at the same time, a positive voltage was being applied to the plate of the trigger tube. They were therefore working this tube in what is termed the second quadrant which is frowned upon by tube manufacturers, who state that the tube operation in anything but the first quadrant will cause the operation to be very erratic and unstable. Operation in the first quadrant calls for a positive potential on the control grid and apositive potential on the plate of the trigger tube. It is an object of the present invention to so connect the trigger tube that itis operated in the first quadrant.

Another object of the present invention is the control of the sensitivity of the phototube in a novel manner. Standard methods known to us,

use a series resistor from the high voltage power supply so asto raise or lower the total voltage across the phototube. Another dimculty with this type of control is that if the total voltage is reduced too much the output of the tube drops excessively with resultant erratic response from the phototube. It is an object of the present invention, therefor, to maintain the total voltage fixed and to vary the voltage of one of the dynodes of the phototube in'a potentiometer type circuit. In this :manner we obtain a control which has a much greater range 'of sensitivity than the series type mentioned above.

A further object of the present invention is to incorporate certain safety devices so that upon failure of current or failure of important portions of the apparatus, the X ray tube will be protected.

Still afurther object of the invention is the incorporation of an interval timer in combination with the photoelectric timer so that if the latter fails to terminate the X-ray exposure within a safe time limit, the interval timer will take over.

Other objects and advantages of our invention will be apparent from the accompanying drawings and description and the essential features thereof will be set forth in the appended claims.

The drawing is a diagram showing one manner of applying our invention.

A source of alternating current at the usual potential of about '115 volts is indicated at Ll L2. Connected between these lines is line [0 including a push button I l which is used to cause an X-ray exposure. In series in this line is a relay [2 having three armatures in, 422) and l2e which are indicated in dot-dash lines adjacent the relay but are repeated in full lines in the proper place in the diagram. This is done to simplify the diagram. Also connected across the source Ll, L2" by means of line 8 is the primary [3a of a power transformer 53. This transformer has several secondaries as indicated at 13?), I30, l3d, 36 and 13]. A peaking transformer It has a primary lid connected by line It to the source Li, L2. In series in this line is a resistor It and the'armature l2?) of the relay l 2 mentioned above. The secondary lib of transformer It is connected to the control grid llc of an exposure initiating tube ii of the Th'yratrontype through a resistor it. The filament Me of this tube is supplied from the secondary it?) of the transformer I3. The plate lla is connected in a circuit which includes line 19, armature of relay l2, relay 28, line 2!, resistor 22, line 23 and the cathode l'ld. It results from this circuit that upon closing the push button H, the relay I2 is immediately energized and this closes the plate circuit of tube ll through the armature I20. However no current flows because of a negative bias on the tube I? as will presently be described. At the first positive voltage peak through the transformer I4, the control grid I'Ic becomes positive and the tube I7 passes current through the plate circuit described so that relay 2c is energized. This relay has an armature 25a shown near the bottom'of the diagram and through a circuit to be more fully described later and immediately energizes a relay 2c which closes the contacts 25 which completes a circuit to the X-ray transformer so as to initiate anexposure. .The tube I'I, having a direct current energizing source remains locked in until the armature I2c opens. It is thus possible to utilize the positive impulse through the peaking transformer I4 and the time delay until contacts 25 close, to close the circuit to the X ray transformer at a point of zero potential.

A source of rectified current is provided for tube I? and for certain other purposes as will presently appear by means of the secondary I30 of the transformer I3. A rectifier tube 26 is provided having a pair of plates 26a connected to opposite ends of the secondary winding I30 which has a central tap for the line 21 which of course will be the negative side of the rectified circuit. The filament 26b of the tube is supplied from the secondary. I311 of transformer I3. This filament is connected'to line 28 which is the positive side of the rectified circuit. The rectified current is filtered by. resistor 22 and condenser 29. This rectified current is supplied to the plate Ila of tube I'I previously mentioned. The negative side of the circuit, line 27, is connected through line 39, transformer winding lb and resistor I8 to the control grid Ilc giving the same a negative bias until overcome by positive peaks from transformer I4 as previously described. The screen -grid ilb isconnected by line 23 to a tap 22a which is more positive than the point 22b.

A trigger tube 3! is shown as of the cold cathode 'type although it will be understood that a hot cathode or filament type tube might be substituted. The plate 31a. of this tube is connected to line 28 through relays 32 and 33 in parallel. These relays have arinatures 32a and 33a for purposes Which will later appear. The cathode '3 lb is connected to line 21'. The grid 3Ic is connected through resistor 34 to ground for a purpose which will later appear.

A phototube of the above-mentioned Zworykin type is diagrammatically shown at 3 3. This tube .has a plate 3 3a, a cathode 34b and a plurality of dynodes 340 which are numbered from one to nine. It should be understood that this showing is purely diagrammatic and that dynodes in the .Zworykin tube are actually staggered to produce a particular multiplying effect. The current supply for the phototube is provided through transformer 35 which has a primary 35a connected between lines LI and L2 .by conductors 35 and 3?. Avoltage regulator tube 38 is provided having a plate 38a connected to one end of the winding 35a and a cathode 38%) connected to the other end of the samewinding. This stabilizes the voltage supplied at transformer 35. A variable resistor 39 is provided in line 37. The output of the sec- 'ondary 35b of transformer 35 is rectified through tub 40 which has a plate 40a connected to one end of the winding 35b and a filament 4% which is supplied through lines AI and 62 from the secondary l3? of transformer I3. The negative side of this rectified circuit is connected through line 4 end of resistor 4d. The positive side of therec tified circuit is connected through line 45, variable resistor 56, fixed resistor 41 and resistors 48 and 39 in parallel, with the negative end of resistor W. This rectified current is filtered through condenser 50 and resistor 5|. Suitable taps on resistor 44 supply dynodes one to eight inclusive of the phototube. The ninth dynode is connected to switch 52 which in the full line position shown in the drawings engages contact 52a for radiography. This contact is connected through line 53 with a tap on the adjustable resistor 48. Switch 52 may also be moved to the dot-dash position to contact 522) for photofiuorography The contact 5% is connected by line 54 with a tap on the adjustable resistor s9. By making the voltage on number 9 dynode equal to that on number 8 dynode there is provided a minimum sensitivity of the photo'- tube. Making the number 9 dynode approximately 100 volts higher than the number 8 dynode gives a maximum sensitivity. The series resistor 46 is used as a calibrator. The phototube units are sent out fully assembled including the parts within the broken line 55. By adjusting the resistor (it, each phototube unit may be adjusted to the same sensitivity so as to give identical output.

A capacitor 56 is pro-vided for collecting the electrons from the anode 34a of the phototube until a sufiicient charge is collected to fire the trigger tube 3 I. This condenser is connected with line 51 which in turn connects the anode 34a of the phototube with the cathode 3Ib of the trigger tube. The other 'side of the condenser is grounded through line 58. The capacitor 56 is normally short-circuited through line 59 and switch 200 until an exposure starts. At that time, the switch 200 opens and the capacitor begins to collect a charge. capacity of the capacitor 56, the potential to which it is charged in order to fire the trigger tube and the sensitivity of the phototube, an exposure may be terminated when a recording film has been properly exposed.

As previously stated, we work the trigger tube in the first quadrant'in the following manner. The grid 3Ic of the trigger tube is maintained at ground potential. The potential of the cathode 3Ib is then raised in a negative direction as it receives charges from electrons collected atthe anode 34a of the phototube. Making the cathode 3Ib negative with respect to the grid 3 I0 is electrically the same as making the grid positive with respect to the cathode and since wehave the plate 3Ia. at a positive voltage, we are'working the trigger tube in the first quadrant. Thus, we are able to get stability and longlife without the use of any amplifier tube such as has been attemped by others as previously explained.

The capacitor 56 as described above in one form of our device has a capacity of .01 microfarad for use in radiography carried out in the fashion disclosed in United States Patent No; 2,401,289 mentioned previously. We may also equip our device with another capacitor 60 which, by means of lines SI and 62 and switch 63 may be connected in parallel with the capacitor 56 by throwing the switch 63 to the dot-dash posicopending application at Edwin R. Goldfield.

By proper selection of the drawing.

"passes through line l6 and relay Tl. terminate the X-ray exposure if it has not prenob'ert J. stava and Edgar-J. Bastin, Jr.,=seria1 N0. 24172, filed ct0'ber 24, 1945, now Patent 23961089. Sensitivity" adjustment for radiography and photofiuorography is maintained by means of the potentiometers 48 and 49'respectively. The dot-dash ' line connecting switches 52 and 63 indicates that these switches are ganged to move 'taneously in one position and engage 52b and 53b simultaneously inth'e-o'ther position. -Me'an's ispiovided for terminating an exposure after a predetermined interval in case the photo timer should fail. This means includes a'trigger tube '64 of the Thyratron type having-an anode 64a, a screen grid 64b, a control grid 64C and a cathode 64d. The filament s le'is energized through lines E and'se which are connected with the secondary I 3 of the power transformer l3. A condenser e1 normally floats across the line Ll, L2 in charged-condition. Thischarging circuit comprises line 68, resistor 69, cathode 64d, grid 64c,

resistor l a, line .1 l variable resistor 12, line 66,

transformer winding l3f, 1ine65 and 1ines13 and M. The switch 2% between lines 68 and "is normally in open position as indicated in the At the start of an exposure, switch '2b is moved'tobonnectlines-Gfi and 14. This stops the charge of condenser 61 while connecting the cathode 84d to L2 and the plate 64a to Ll. The condenser 6'1then discharges'slowly through a resistance bank i'n'dicated at 15. A rough time adjustment maybeobtained in that portion of thebaiik indicated at 'iEa'while a finer adjustment may be provided at b. Thenegative'plate of the condenser 67 is-connected to the control "grid 64c and no current will pass tube 64 until the charge has leaked off condenser 6'! to the threshold of tube 64. When control grid 64c passes this pointthe tube 64 fires and current This will for the purpose of correctingthe interval timer for variations in line voltage.

The winding I3 is so connected'in thecircuit for charging condensert'l'that its voltage bucks the charge voltage and therefore-an increase in the linevoltage will automatically decrease the charge on condenser Bl which' willdecrease the time interval necessary to fire tube 64.

For the purpose of indicating the general control of theX-ray exposure a number of switches have been assembled in the wiring diagram at one end thereof so as to illustratethe various ways in which the'exposure maybe made or broken. This series of connections beginning at Ll comprises the relay winding 2:2 which controls the contacts 25 which energize the X-ray transformer during an exposure. Next comes the switch 2a which is energized by the relay' previously described. The switch 86a is'normally open but is -closed-immediately'upon the energization of the winding H3 ofthe power transformer i3. Upon 'i'ailure of this power supply, relay 80 would be deenergized and swit'chfill would open. Line iii connects switch Sllwto switch 'llo which is'nor- "m lll los d ea nstthecontacttz asshowndn "him to record "X-rays'which havepassed through photofluorography itengages contact oil).

brokenline-Eii indicates that this swtich insiee:

tube assembly.

the drawing when relay' 'ilis deenergized. If the intervaltimeroperates soas to energize relay ll in the manner described above, the switch Tia engages contact 83 which will light a lamp '34 'or other'signal-to indicate that the interval timer has terminated the exposure rather than the photo timer. At the same time that switch 11a engages contact-B33 it-completes a circuit through lines 85, 86 and (it toenergize relay cc which is in line 85. This'relay has an armature 88c which is normally open as shown in the drawing but which closes upon energization of relay '88 so-as to lock the-relay in'through lines and The signal 22% therefore remains energized so that the operator will make the necessary corrections to "return to'the control of the photo timer.

The'line connects switch @162 to switch 32a which is normally closed butisopene'd by energization of relay 3T2 whentrigger tube 3| fires upon operatiorr'of the photo timer to terminate the X-ray exposure. 'I'he line t'l leads to aswitch fill which ganged with switches 52 and as indicated by the dot dash lineconnecting them. For radiography the switch engages contact his and for thephoto timer assembly. Outside of this assembly is-ani'anual switch'ii? having positions silo and 92b corresponding respectively to the:

'toenergize the peaking transformer 54. It also closes switch [2c in line it so as to place the relay 2!? in circuit with tube ll. Upon occurrence of the first positive peak in transformer winding use, tube fl passes current and energizes relay This closes switch 2501 which energizes relay at to close the X-ray transformer contacts 25 a predetermined'tinie after the potential peak from transformer i i and, as previously mentioned, this is so adjusted as to close the X-ray transformercontacts at zero potential. As previously mentioned, the switch this is closed when power transformer is is energized providing the winding [3 is in proper condition. Relay 20 also closes'switch 2% connecting lines it and 58 so as to cause the interval timer to begin its operation as previously described. Relay 2 also opens switch 200 in line 55. so that capacitor 55 (or 55 plus E50) begins to collect a charge for the opera tion of thephoto timer as previously described.

If'thephoto timer terminates the exposure by firing of the tube 3!, relays 33 and 32 are energized. Relay 33 when energized will open switch 330: in line 76 of the interval timer circuit so as to reset that timer for the next operation. Relay 3 2 will open switch 32a to deenergize relay 24, permitting contacts to open and terminate the X-ray exposure. Upon the release of button it relay i2 is deenergized and the'circuit switches 12a, 12b and I20 are returned to their original positions so as to set the parts for another operation.

1.In apparatus-fortimingthe exposure of a a body and are incident upon a fluorescent screen,

7 whereby electrons from said phototube anode may charge said trigger tube cathode negatively to cause said trigger tube to fire.

2. In apparatus for timing the exposure of a film to record X-rays which have passed through a body and are incident upon a fluorescent screen, thecombination of a phototube having an anode and a light sensitive cathode and multiplying electrodes, a trigger tube having an anode and a cathode and a control grid, switch means operatively connected with an electrical circuit sensitive to firing of said trigger tube for terminating said X-ray exposure, an electrical circuit normally biasing said trigger tube beyond cutoff, a capacitor in circuit with said phototube and said trigger tube, and an electrical connection from said anode of said phototube to said cathode of said trigger tube, whereby electrons from said phototube anode may charge said capacitor to a potential sufiicient to charge said trigger tube cathode negatively to cause said trigger tube to fire.

3. In apparatus for timing the exposure of a film to record X-rays which have passed through a body and are incident upon a fluorescent screen, the combination of a phototube having an anode :and a light sensitive cathode and multiplying lelectrodes, atrigger tube having an anode and :a cathode and a control grid, switch means opieratively connected with an electrical circuit sensitive to firing of said trigger tube for terminating said X-ray exposure, an electrical circult applying a positive potential in the plate circuit of said trigger tube, an electrical circuit normally maintaining said control grid at a relatively fixed potential below the threshold of said trigger tube, and a capacitor in circuit with said phototube anode and said trigger tube cathode andso arranged that electrons collecting on said phototube anode may charge said capacitor to a potential sufiicient to charge said trigger tube cathode negatively and to cause said trigger tube to fire.

4. In apparatus for timing the exposure of a film to record X-rays which have passed through a body and are incident upon a fluorescent screen, the combination of a phototube having an anode and a light sensitive cathode and multiplying electrodes, a trigger tube having an anode and a cathode and a control grid, switch means operatively connected with an electrical circuit sensitive to firing of said trigger tube for terminating said X-ray exposure, an electrical circuit applying a positive potential in the plate circuit of said trigger tube, an electrical connection from said control grid to ground, an electrical connection from taps connected consecutively to the other multiplying electrodes of said phototube to render them consecutivelymore positive, whereby said electrode nearest said anode is used to vary the sensitivity of said phototube.

6. In a phototube for timing the exposure of a film to record X-rays which have passed through a body, said phototube being of the type having an anode and a light sensitive cathode and multiplying electrodes, the provision of a resistor having spaced taps connected consecutively to all but one of said multiplying electrodes to render them consecutively more positive, and separate means for varying the potential of said one of said multiplying electrodes to vary the sensitivity of said phototube.

7. In a phototubefor timing the exposure of a film to record X-rays which have passed through a body, said phototube being of the type having an anode and a light sensitive cathode and multiplying electrodes, the provision of a resistor having spaced taps connected consecutively to all of said multiplying electrodes except that one of said electrodes in circuit nearest said anode of said photo tube to render said electrodes consecutively more positive, and separate means for varying the potential of that one of said multiplying electrodes in circuit nearest said anode of said phototube, whereby to vary the sensitivity of said phototube.

8. The combination of claim 3 including an interval timer having a second trigger tube. means biasing a control grid of said second trigger tube beyond its firing threshold and including a second capacitor in charged condition, means normally charging said second capacitor to a predetermined potential, resistor means in circuit with said second capacitor to provide a controlled leaking oil of its charge to a point where said second trigger tube will fire, means responsive to firing of said second trigger tube for terminating said X-ray exposure, switch means normally short-circuiting said first named capacitor, and means operable by initiation of an X-ray exposure for opening said short-circuiting means of said first named capacitor and for synchronously interrupting said second capacitor charging means, whereby two alternative timing. circuits are available for terminating said X-ray 'exposure.

9. The combination of claim 1 including two separate fixed resistors adapted to be placed alternatively in circuit with one only of said multiplying electrodes for varying the potential of said one of said multiplying electrodes, and switch means for connecting a selected one of said fixed resistors in said last named circuit whereby to provide two alternatively selected fixed sensitivities for said phototube.

JACK BALL.

EDWARD B. GRAVES.

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

UNITED STATES PATENTS Number Name Date 2,159,755 Zworykin et al May 23, 1939 2,244,137 Bischoff et al. June 3, 1941 2,252,752 Bliss Aug. 19, 1941 2 ,401,289 Morgan et a1 May 28, 1946 2,417,023 Sweet Mar. 4, 1947 2,441,324 Morgan et al May 11, 1948 2,454,168 Hartwig Nov. 16, 1948 2,459,632 Engstrom Jan. 18, 1949

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