US1003325A

US1003325A - X-ray system.

Info

Publication number: US1003325A
Application number: US58403710A
Authority: US
Inventors: Eugen Blum
Original assignee: KNY SCHEERER Co
Current assignee: KNY-SCHEERER Co; KNY SCHEERER Co
Priority date: 1910-09-27
Filing date: 1910-09-27
Publication date: 1911-09-12
Anticipated expiration: 1928-09-12

Description

' 1 1119111611 Sept.'12, 1911.

2 SHEETS-SHEET 1.

WITNESSES MIVENTOR Eugen Blum ATTORNEY E. BLUM.

X-RAY SYSTEM.

APPLICATION rum) SEPT. 27, 1910.

Patefited Sept 12, 191i.

- WITNESSES .Euygn Blum A EUGEN 'BLUM, OF UNION HILL, NEW JERSEY, ASSIGNOR TO THE KNY SCHEEBER 7 m srArEs PATENT oF-nIo-E.

COMPANY, A CORPORATION OF NEW YORK.

X-RAY SYSTEM.

Specification of Letters Patent.

Patented Sept. 12, 1911.

Application filed September 27, 1910. Serial No. 584,037.

' To ,all whom it my concern:

tain new and useful Improvements in X- Ray Systems, as specification. k This inventionrelatesto terns for high potential alternating current and particularly to those adapted especiallyset in the following for X-raywork..

' An object of the invention is to eliminate disadvantages present in rectifying systems previously known and atthe same time to maintain the advantages of such systems.

Previously known types of rectifying systerns are exemplified in the patent to Lemp 774,l38',-Novemb.er 1, 1904, and in the patent to Snook, 954,056, April 5, 1910. In a system such as that of the Lemp patent portions only of either the or waves are available in a working circuit. In a system such as thatof the Snook pat ent the rectification is such that corresponding portions of both the and waves are available. The disadvantages inherent in each of these systems will not be enumerated specifically but rather the advantages attained-by the applicants system.

On account ofthe disastrous effect upon 7 the human body of too frequent exposure to the X-ray ithas'become customary to inclose the operator in a cage of material impervious to 'the-i'X -ray. f This cage is pref- -er'ably locatedgat soine distance from the X-. "ra tube. It. isexpe'dient that the operator be able tocontrol and make readings of the generating current for the X -ray without leaving his protecting cage, Consequently the various meters and controlling instru- .1nentsshould .be located preferably withins a'ge- Current of extremely high potential, pref- Tably upward ofl OOTkilo-vblts, is desir f It is alsoalm'o'st a necessity to be able to meter the current flowing ini the working circuit in order that the operator may dectifying sys termine and regulate the operation of an X ray tube. For his safet and convenience this necessitates the locatlon of the amperemeter for the Working circuit within his protecting cage.

Themos t practical method of attaining high potentials is by means of the transformer, although this has the defect of delivering from its secondary a potential of alternating sign, whereas a pulsating cur- I rent is a necessity for the best operation of an X-ray tube. By rectifying the alternating current delivered by a high potential transformer it has heretofore'been possible to operate X-ray tubes with a considerable degree of satisfaction; In systems employing transformers no difficulty has been experienced in controlling the primary low potential side of the transformer from the operators protecting cage.

In addition to'making possible the location of all controlling instruments for the low potential side of the transformer it is an objectv of the resent invention to make possible the safe installation within the operators protecting cage of an ampere-meter for the high potential working circuit. To

this end a transformer having a two-coil secondary winding is employed although in the broad aspect of the invention the tvxo coils of this secondary winding should be understood as being two independent sources of alternating current of the same frequency. The expression alternating current is employed to designate generally both a true alternating current and also one in which the current cycle may have any form provided it regularly changes from to even thoughintermittent, periods of no current be present. l p Y '1;

In addition to rectifying the current supplied to the working circuit, the iiivention provides a'- rectifying interconnection of the two sources of alternating current'whereby a directcurrent ampere-meter maybe cut in series between the two said sources of alternating-current at what is in effect a neutral point which may be grounded at one of the terminals of the ampere-meter, By

ployment of two sources of alternating current instead of the employment of a single source of double the potential of either contributes to this end and makes possible the en'ipleyment in the applicants rectilicr construction of a simple cylindrical cou'unutze tor, between adjacent brushes for which the fulhpotential tor the workingcircuit is never present. This does away with the;

necessit of extensive insulatiim artitions such as those described in the patent to Snook referred to above.

The above and further objects of the invention Will be set forth more in detail in the following claims and-will be more apparent from the following description .which should be read in connection with the accompanying drawings, illustrating embodiments of the invention, in which like characters designate corresponding parts, and in which,

Figure 1 is a diagrammatic representation of one embodiment of the invention; F ig. 2 is a diagrammatic representation of unrectified potential-Waves for the transformer of Fig. 1; Fig. 3 is a diagrammatic representation of the rectified waves for the trans former of Fig. 1; Fig. L t is a diagramn'iatic representation of a preferred en'ibodiment of the invention; Fig. 5 is a cross-section through line VV of Fig. a; Fig. (3 is a I diagrammatic representation of the unrectitied potential-waves for the transformer of Fig. 4; Fig. 7 is a diagran'nnatic representation of the rectified potential-waves for the system shown in Fig. at; Fig. 8 is a diagrammatic representation of rectified waves delivered at one pair of terminals of the system of Fig. l; Fig. 9 is a similar diagram showing the rectified waves delivered at the other pair of terminals of the system of Fig. i; and Fig. 10 is a diagran'nmitic representation of a modification of the stationary t 'ansformer so as to comprise two independent transformers particulary adapted for energization from a poly phase circuit.

In the practical embodiment of the invention it is many times expedient to employ direct current as the original source of.

power, which in the embodiment of the invention shown is supplied by the

mains

1 and 2 connected to the direct current end of the inverted rotary converter '5, which in the rent at the collecting brushes l and 13, one

complete cycle correspondiug to one rotation of the converters rotor.

it is. or course, to he iln lrrslood that single phase alternating current may be bcttcr available than direct current. in which event lhe tlliiCl'lltlllllQf curl-rut mains should be connected to the terminals {l and 5. in such case the electric unit acts merely as a synchronous motor, as will be understood.

The second part o I the sy by It and comprises a ti'aiisloiiiici' and rcclitying means.

in Fig. l. (l indicates a magnetic core oli the closed circuit type tor the igrair rlornier 'l, which should he built according to approved transtoiiner-core construction. l t is shown rectangular and mounted synunclrically to rotate with the attached shalts T and S journalcd respectively in bearings fl and 10, the shaft 7 being adjustably clutched to the shalt ll of the unit :3 by means of the coupling 12. The core t has a prin'iary winding 13 shown in dotted lines and disposed with an equal number ot turns about each of the legs lkland 1.3. The terminals oil. this prin'iarv winding 13 are connected respectively to the rings 10 and 1'7, cooperating with brushes l8 and 1.9, which in turn may be connected respectively with the brushes 5 and l by means of the wires and 21 to complete the primary circuit.

The secondary tor the core (3 comprises two

equal coils

22 and 2 of an appropriate number of turns each greater than the numher in each corresponding primary coil and preferably wound over the primary coils according to the most approved translformcr constrnc ion to prevent magnetic leakage and to give a minimum shitting of phase for the secondary current with rcsp ct to secondary electro-motivc force. Fiacli ol these secondary coils 29 and 22' constitutes a source of high potential alternating current and is so regarded in this 8])(10llltf2ltl0l1. The attaching strips Q-l and are secured to the core (5 as shown to provide for the mounting of

terminals

26 and 27; 28 and 2E); and 30 and 31, which preferably terminate all equidistant from the axis ofrotation oi the transformer and in the same plane. 26 and 27 are respectively the J: and terminals for the secondary coil 22.

30 and 31 are respectively the r and the tern'iinals for the secondary coil 23.

28 and 29 are terminals electrically connected with the core (3, which in turn is connectcd to ground. by the shatt 8 and journal 10. p

and 33 are stationary contacts for cooperating with the terminals 26, 97. 30 and 31 and are respectively connected by leads cm is denoted terminal 37 of the working circuit, which in this embodiment includes the X-ray tube X.

38 is a stationary contact cooperating with the

terminals

26 and 27.

39 is a bridge contact for cooperating with the

terminals

28,29 and 30, 31. The contacts 38 and the journal are connected through leads and 11 to the terminals of direct current milli-ampere-meter MI The leads 40 and 41 are shown in part broken to denote that they may be of any desired extent permitting the location of the meter M at a distance, in which event it may be desired to provide the lead-41 with an additional ground G in the neighborhood of the meter itself.

' In Fig. 2 the sine wave 12 diagrammatically illustrates one complete electro-motive terminals.

force cycle for each of the

secondary coils

22 and 23 while the sine wave 4:3 indicates on the same scale the electro-motive force cycle for the complete secondary winding comprising the two

coils

22 and 23 in series. As is obvious these are the usual alternating current waves and involve a change in sign.

In Fig. 3 the portions 7) and p indicate the portions of the electro-motive force wave d3 rectified and as they are applied to the terminals 36 and 37 of the working circuit, p being a portion ofthe part of cycle 43 and p being a corresponding portion of the part of the cycle 13, but rectified to be a +.wave part.

Operation for Fig. 1.-Any and all of the well known regulating and measuring devices for electric circuits may be employed in connection with the mains 1. and 2 to start the unit 3 and in connection with the -"wires 20 and 21 to regulate'the current flow in the primary 13. The rotation of the shaft 11 causes a synchronous rotation of the transformer T and its attached secondary The angular o'sition of trans former T may be adjnstet as-desired with respect to the motor shaft 11 according to the location desired for the wave parts 79 p by a suitable adjustment of the coupling 12,

and as will be obvious to those skilled in the art. The

various terminals

26, 27, 28, 29, 30 and .31 make and break contact simultaneously with their cooperating stationary con tacts. \Vith the contacts in the relative positions illustrated, the first quarter of the cycle indicated in Fig. 2 has been completed; the 1*; terminal 26 of secondary coil 22 is in working connection with stationary contact 32,.leading to the working circuit; and the F terminal 30 ofsecondary coil 23 is in working connection with the stationary contact 33 leading Working circuit. The secondary circuit for this positionmay be traced as follows secondary source 22, out what is now the terminal 26, stationary contact 32, lead 3%1,

to the other terminal of the I terminal 36 of the working circuit,ternnnal 37 ofthe working C-l-lclllt, lead 35,

contact 33. terminal 30,-secondary source 23, 4

terminal 31, bridge 39, terminal 29 core 6,' shaft 8, ournal 10, lead 41, (connected with ground G), meter M, lead 4-.0, contact 38, terminal 27, back to secondary source Since the terminal 31 is now instantaneously the meter lead a1 is consequently positive, and the directioll of current fiow in the meter M is indicated by the plus and, minus signs appliedthereto.

\Vith the partsin the positions shown, the terminal 26 is instantaneously while theterminal 30 is instantaneously The wave part p is delivered to the working circuit terminals. The meter M is cut in in series between the

secondary sources

22 and 23 and, therefore. at the neutral point of the trans former secondary which is grounded at G.

Upon a half rotation of shaft 7 the threefourths point for cycle 43 reached and

terminals

27 and 31 are-caused to contact respectively with brush contacts 32 and while terminal 26 is caused to contact with brush contact 38 and terminals 28' and 30 are caused to be bridged by the brush contact 39. At this instant the

terminals

27 and 30 have become and the terminal 31 has become so that similar circuit to that previously traced is produced to cause a cur. rent flow through the working circuit and meter M in the same direction as the former current flow, the wave part p being applied.

This current flow is a pulsating one for X- ray work and its intervals of flow may correspond to any particular fraction of each secondary current wave corresponding to a commensurate fraction of each secondaryelectro-motive force wave as indicated in Fig. 3, in which 79 7) indicate the fractions being employed by the system of Fig. 1.- The actual location of the fraction employed on its wave may be adjusted by the sleeve 12 and its extent or duration is regulated by the angular extent about the shafts 7 and 8 of relative contact between the terminals26, etc. and their coiiperating stationary contacts 32, etc. With the extremely high potentials employed, it is well. known that actual contact between the terminals 26, etc.

and the contacts 32, etc. is not actually a necessity, it being merely necessary to reduce the air gap therebetween to a small distance. For the reason the

contacts

26, 27, 28, 29, 30 and 31 are not shown as actually physically contacting with their stationary cooperating contacts although such physical contact is not precluded by the nature of the invention.

Emlbodz'nwnts of Figs. 4 a mi 5.-In many instances it is preferred that the transformer of the installation It be stationary instead of rotated, as shown in Fig. 1. Such an embodiment is shown inFig. 4. In this winding 113, the terminals of which are connected to a source of single phase alternating current by the

leads

120 and 121; the secondary winding hav ng-two

coils

122 and 123 of the same number of turns each insuring a minimum and wound preferably in close relation to the primary winding 113; and a core having preferably a closed magnetic circuit, as shown in the embodiment of Fig. 1. It should be understood that this transformer T may be constructed according to well known approved transformer construction, amount of iiiag netic leakage. Various leads 14 may be tapped out of the primary 113 to provide for varying the number of ampere turns in the primary circuit-in a manner now well known in the art, while the dotted'portion of the

leads

120 and 121 indicate that the same may be of indefinite length to provide for the insertion of any of the well known controlling devices such switches, rheostats, nieters, etc. The two

secondary coils

122 and 123 may each be regarded as a source of alternating current of the same frequency. 126 and 127 indicate respectively the and i terminals of secondary coil 122 and are shown'in the form of diametrically 0pposed brush contacts. 130 and 131 indicate respectively the i and F terminals of secondary coil 123 and are likewise shown in the form of diametrically opposed brush contacts. v is extended longitudinally through the journal 10 and has fixed thereto the rectifying commutator 15, carrying a pair of

alined segments

16 and 47 located respectively at the opposite ends of the commutator; and a pair of laterally spaced

inner commutator segments

48 and 49 diametrically opposed to the segments 11; and 417. In the preferred construction for X-ray work each segment encircles approximately .70 of the commutator 45 which should be constructed according to improved commutatorconstruction of high quality insulating material. The cross section of- F ig, showsa satisfactory construction for this commutator.

Between the

brush terminals

126 and 130 is a pair of

brush contacts

50 and 51, cross connected respectively by wires 52 and with a pair of diametrically opposed brush contacts 54 and 55. The leads 40 and 41 of the direct current milli-ampere-meter B1 are connected respectively as shown to the

brush contacts

50, 54 and 51, 55, the lead elbeing grounded-at one or more points The terminal 136 for the-working circuit is connected by lead 134 to brush contact 132 while the terminal 137 of the working circuit is similarly connected by lead,,.:l35

In'tliisembodiment the shaft 7 with the brush contact 133-

Contacts

132 and 133 are symmetrically positioned. toward the outer edge of the commutator 415 and have diametrically opposing them the similar brush contacts 56 and 57 which are connected respectively by leads 53 and 59 to supplemental working circuit terminals (30 and 61 and are provided with switches (32 and 63 for cross connection to the leads 134; and 135 respectively.

Inasmuch as the electro-niotive force cycle for each of the

sources

122 and 123 may be represented by the line 6 1 of Fig. 6 indicating that they are both. not only of the same frequency but in phase, the

brush contacts

132, 126, 50, 51, 130 and 133 have been shown in the same plane with, the diametrically

opposed brush contacts

56, 127, 5 1-, 55, 131 and 57; also the segments 48 and 419 have been shown occupying thesame angular position diametrically opposite to the segments 16 and $7 of the commutator However, as will be understood by those skilled in the art, should the current of source 122 be out of phase with that of the source 123, all that is necessary properly to add the electro-niotive forces of these two sources to produce the combined wave (35 of Fig. 6, is to cause a relative angular shifting of the commutator parts for one of the

sources

122 and 123 relatively to those of the other. For iiistance, the contacts and segments at the right of the central zone of the commutator 415'may be shifted angularly relatively to those at the left a suitable number of degrees to offset any shifting in phase between the two

sources

122 and 123.

Operation for F rigs. .4 and 5.The wave diagram 6st of Fig. 6 shows the elect-romotive force. wave for each of the

secondary coils

122 and 123 which, if combined by cross connecting unlike terminals such as 127 and 131, would produce the electro-motive force wave ($5 of Fig. (i, it being understood, of course, that the diagrams of Figs. 6 iiidicatethe iinrect-ified electro-motive force waves. For some purposes, it is desirable to employ a part of each electro-motive force wave (both and for the working circuitand in X-ray work these waves must be rectified so as to tend to cause the passage of current waves in the working circuit always in the same direction. For example,

the parts g g and 9', shown in Fig. 7,

may be desired. \Vith the connections as shown in Fig. 4, the working

circuit terminals

136 and 137 are capable of delivering such electro-motive force pulsations. For the position of the parts indicated, the negative working circuit terminal 137 is connected by lead 135, through switch 63, lead 59, brush contact 57, segment 47, with what is now the negative terminal 131 of source 123. The path continues through coil 123 out what is now the terminal 131, thence and 123 and thissecondary is grounded at itsneutral pointfito .the ground G con-v nected to lead 41. Also'the ampere-meter M is connectedin series or out into this sec ondary winding at its neutral point so that the direction of flow is-infac eordance with the and signs applied to the amperemeter M, that is from lead 41 to lead .40.

When the commutator 45 has been rotated 180 corresponding to the threequart'ers point 65' of the electro-motive force cycle of Fig. 6, segment 46 is bridging

contacts

132 and 12,6; segment 47 is bridging

contacts

130 and 133; segment 48 is bridging contacts 147 and 54; and segment 49 is bridging contacts 55. and 131. Under these conditions the secondary circuit vfrom terminal-1'13? continues through lead 145, contact 133, segment 4'7, contactr130, which is now the terminal o f coil 123, through coil 123, contact 131, segment 49, contact 55,

wire 53, lead'41, ampere-meter. M, lead 40,

wire '52, contact 54, segment 48, terminal 127 of coil-i122, which 'is now negative, through coil 122, terminal 126 '(now segment 46, contact 132, lead'134, to the terminal'136 of the working circuit. Thus, under these conditions, the current flow through the ampere-meter M is also as indicated by the and signs, from'lead 41 to lead 40. An electro-motive force impulse corresponding ill Q of Fig. 7 is, therefore, applied. Upon each 180 rotation of. the commutator 45 successive im pulses such as. g etc. are applied to the terminals. It is well understood, of course, that there may be a displacement in phase between the secondary electro-motive force and the secondary current, although it may be minimum in this system. This, however, may be rectified merely by the proper angular adjustment of the commutator parts.

The electro-motive force'waves have been lllustrated dlagrammatically because, obviou'sly,.a current wave is dependent upon the creation of an electro-motive force wave and the latter isalways present during the operation of the machine whether or not the working. circuit is closed.

It is sometimes desirable that impulses of half frequency be delivered to a working circuit, It is also} sometimes desirable to energize two separate working circuits with impulses identical in frequency and in strength. lVith the apparatus illustrated in Fig. 4 this may be accomplished through the medium of-the switches 62 and 63. By opening these switches the working circuit terminals 60 and 61 will deliver waves cor responding to the wave parts 0'- and r of Fig. 8, while the

terminals

136 and 137 will deliver waves corresponding to tlieivave parts 5 and s of Fig. 9, the wave parts of both Figs. 8 and-9 being identical insign,

potential and frequency, although those of Fig. 8 alternate with those of Fig. 9 and are a half cycle out of phase therewith.

' In connection with the commutator 45 of Fig. 4 and its associated parts particular attention is called to the fact that the maximum potential corresponding to the electromotive'force wave 65 is carried only to the opposite ends of the commutator 45, by which arrangement many insulation diificulties are eliminated. Also middle contacts, such as 50, 54 and 51, 55 are always practi-. cally of the same potential neutral tothe endmost contacts and substantially equal to the potential of the earth by reason of the ground G. The leads 40 and 41 are, therefore, safe to extend into the operators protecting cage and require very little insulation notwithstanding the fact that the entire secondary current flows through them and the ampere-meter M, which-may be a comparatively cheap instrument of the direct current type due to the fact that current impulses always flow therethrough in the same directiom asl has previously been explained. p

Since the 'electro-motive force waves of the two

sources

122 and 123 may be out of phase and still be rectified and combined, it may be desirable" to employ a two-phase power circuit with one phase energizing coil 122 and the other phase energizing coil 123 in any suitable manner as for example, through the medium of independent primary windings, such as the primary wmdings 113 and 113" for the transformers'l" and T, shown in Fig. 10. The out of phase relationbetween these two sources is compensated for or practically annulled by merely giving an angular'displacement, lead or lag, as the case may be to the

segments

47 and 49 and the diametrically opposed

contacts

51, 130, 133, and 55, 131,157 relatively to the similar segments and-contacts shown at the lefttherefrom' in Fig. 4. Such an angular displacement or shifting can be easily understood if the cylinder 45 is considered as consisting of two symmetrical adjacent parts along the shaft 7 and that one of these two parts together with its brush contacts is angularly rotated relatively to the other part so as to assume the necessary leading or lagging position to correspond with the difference in phase between the two

sources

122 and 123.

The embodiments of the-invention shown and described'are in a large degree diagrammatical, as it is to be understoodthat the proper construction of the various parts illustrated is now well known in the art and is contemplated by the applicant. It is also Well understood that other modifications than the two illustrated and described may embody the applicants broad invention and that the same are fully contemplated by the applicant.

What is claimed and what is desired to be secured 'by United States Letters Patent 1s 1. In a rectifying high potential system, the combination with a source of alternating current, of a high potental transformer; a secondary working circuit; a synchronous rectifier for sending current waves all in the same direction through said secondary working circuit from the secondary of said trans former; a direct current ampere-meter; and means for cutting said ampere-meter in series at the neutral point of said secondary throughout each period that a current wave is sent through said secondary working cir cuit to measure the value of the current in said secondary Working circuit.

2 In a rectifying high potential system, the combination with a source of alternating current, of a high. potential transformer; a secondary working circuit; a synchronous rectifier for sending current waves all in the same direction through said secondary working circuit from the secondary of said transformer; a direct current ampere-meter; and means for grounding the neutral point of said secondary and for cutting said amperemeter in at the neutral point of said secondary, throughout each current pulsation of said secondary working circuit, to meas ure the value of the current in said secondary working circuit.

3. In an X-ray system, a source of single phase alternating current; a power shaft rotated synchronously with said current; a high potential transformer having a primary Winding connected with said source and a secondary winding comprising two separate coils; the terminals for a power circuit; a direct current. ampere meter; a rotating commutator-means driven by said power shaft; and terminal contacts for said two separate coils and said ampere meter and cooperating with said commutatormeans for connecting and disconnecting alternate terminalsof said two coils, one of each, with the respective terminals of said ampere meter and for simultaneously connecting and disconnecting the free terminals of said two cells respectively with the corresponding terminals for the Working circuit so that the ampere meter is progressively connected at a neutral point in series between the two coilsand will be traversed by the same rectified current as that delivered to the working circuit.

4. In an X-ray system, a source of single phase alternating current; a power shaftrotated synchronously with said current; a high potential transformer having a primary winding connected with said source and a secondary winding comprising two separate coils; terminals for a working circuit; a direct current a1nperemeter; a rotating con'nnutator means driven by said power shaft for connecting alternate terminals of one of said two coils to one terminal of said ampere-meter and alternate terminals of the other of said two coils to the other terminal of said ampere-meter, all throughout corresponding parts of the electro-motive force wm'es of the said coils and for connecting the free terminals of said coils to the terminals for the working circuit throughout the same'periods, whereby current waves of the same direction only pass through said ampere-meter, the terminals for the working circuit are always of the same sign and one terminal of the am- )ere-meter ma T be rounded to constitute the neutral ondary.

5. In a rectifying high potential system, two sources of alternating current of the same frequency; terminals for a working circuit; a direct current ampere meter; commutator-means driven synchronously with the current alternations of said sources and operative'to connect and disconnect alternate terminals ofone of said sources with one-terminal of-said ampere meter and alternate terminals of the other of said sources to the other terminal of;said ampere meter all throughout corresponding parts of the electro-motive force waves of the said sources and for connecting and disconnect ing thefree terminals of said sources with the terminals for the working circuit throughout the same periods, wherebyeurrent waves of the same direction only can pass through the said ampere meter, the terminals for the working circuit are always of the same sign and one terminal of the ampere meter may be grounded to constitute a neutral point for the system.

6. Inean -X-ray system, a rectifying'commutator comprising a cylinder of insulating material; a pair of segments each spanning less than 180 of said commutator and axially spacedthereon; a second. pair of commutator segments each of the same angular span as the first pair, and'respectively diametrically opposed to the segments of the first pair, and each axially overlapping a part of the corresponding segment of the point for the transformer seccally' opposed segments.

, transformer; a direct current ampere- Witnesses:

first pair and a part of the axial space besecondary of said transformer at a point in- 10 tween thesegments of the first pair; and termediate its full potential poles.

. two diametrically o posed sets of three In itness whereof, I have signed my brushcont-acts each or each two diametriname to the specification, in the presence of two subscribing Witnesses.

7, In an X-ray system, a,high potential EUGEN BLUM.

-meter';f?urrentrectifying means, for con- SIDNEY NEWBORG,

necting said ampere-meter in series with the W. G. ALLEN.