US2636146A - Ion gauge - Google Patents

Description

April 21, 1953 F. c. HURLBUT ION GAUGE Filed May 26, 1,950

Patented Apr. 21, 1953 UNITED STATES PATENT" OFFICE ION. GAUGE Franklin 0. H'urlliut, Berkeley, Califi, assignor to The Regents-"of the University of California, Berkeley; Calilc, a" corporation of California.

ApplicationMay 26, 1950,.S'erialN'o. 164,451

2' Claims. 1 My invention. relates to means especially useful in connection with evacuated. vessels and vacuum processes in general to serve as. a. measuring device.

Ion gages. in. general are. well known and depend for their operation. upon. thev conduct. of electrical charges at subatmospheric pressure. Ordinarily available gages. are subject to. variations inaccuracy from time. to time and are especially subject to inaccuracies due to. changes in the gage structure occurring during protracted use- It is therefore an object of my invention to provide an improved ion gage.

Another object of my invention is to provide an ion gage which can. readily be utilized with sub-atmospheric vacuum equipment of the customary kind.

A still-further object-of. my invention is to provide a vacuum gage in which protracted operation does not seriously aifect the working nor the accuracy of theinstrument.

A still further object of my invention is to provide means for preventing erratic results. due to sputtering'of the filament material.

A still further object of my invention isto provideanion gage mechanicallyarranged and disposed in such a fashion that-it has a high initial accuracy which is maintained throughout substantially the entire useful lifeof the gage;

Other objects, together with the foregoing, are attained in the embodiment of the invention described in the accompanying description and illustrated in the accompanying drawings, in which Figure l is a plan of a portion of an ion gage constructed in accordance with my invention.

Figure 2 is a cross section, the plane of which is indicated by the line 2-2 of Figure 1.

Figure 3 is a cross section, the plane of which is indicated by the line 3-3 of Figure 2.

In its preferred form, the ion gage of my invention is inclusive of an envelope evacuable through a tubular connection, the envelope preferably being of substantially drum shape with the tube connection in one portion of the cylindrical side wall. The two, substantially planar, opposite end walls, are equipped with lead buttons so that the filament, the grid and the anode of the tube are all appropriately supported. The arrangement is such that the anode lead buttons are on the opposite wall from the grid and filament lead buttons and the arrangement is likewise such that sputter shields are interposed between each of the various lead buttons and the filament.

While the ion sage of my invention is. susceptible to various modifications depending partly upon the environment: in which it is'to' be utilized and. depending, in part, upon other factors, it has successfully been embodied and operated as shown herein.

In. this. form of the device, an access tube 6 is provided with a restriction 1 in the customary fashion and leads to a coupling 8 in which is mounted a standard outgassing. bypass valve 9 and a thermocouple lfl' passing. through terminals II and [2. Most of the structures so far described are standard parts of auxiliary appaa ratus and are fabricated of metal. The ion gage of my invention preferably commences with a metallic ferrule l3 adapted to be connected by a band of solder I 4 to the remaining metallic members and including a tapered connection l6 incorporating; a standard metal. to lass seal; for example, a copper to glass seal.

Secured thereby to the ferrule I3 is an envelope [8' preferably of glass. or comparable material, the. envelope being essentially. circular in cross section in one plane and substantially rectangular in. cross. section in the other plane so that it is. generally of drum. shape. Fromthe connection [6,, a flare l9 merges. with the cylindrical wall 2 I ofthe envelope 18. The. envelope is substantially symmetricalon opposite sides of. the flare. l9 and at its opposite ends is closed by a first wall 22 and" by a parallel wall 23, these walls being, fun,- d'amentall'y planar and perpendicular to the general cylindrical axis of the envelope I8.

Approximately in the center of the first wall 22, I provide a filament support post 24 which may be imbedded in but preferably does not extend entirely through the wall 22. Within the envelope I8 the support includes an offset leg 26 leading to a central terminus 21 on the opposite side of the envelope so that a close approach to wall 23 is made.

At appropriate points in the wall 22 and preferably symmetrically disposed with respect to the central mounting 24, are a pair of filament lead buttons 28 and 29, respectively. Each of these buttons is inclusive of a protrusion 3| from the envelope of approximately conical contour and also is inclusive of a metallic conductor 32 extending through the material of the envelope from an external termination, available for connection in a circuit, to an internal terminus. The two filament lead buttons 28 and 29 serve as diametrically opposite supports for a filament wire 33 extending from points adjacent to the wall 22 across the central portion of the drum envelope to rest upon the filament support 21 3 near the wall 23. Thus, the filament stretches across or spans the projected axis of the ferrule IS The wall 22 is additionally provided with a pair of symmetrically arranged grid lead buttons 35 and 31 each of which is of a construction similar to the filament lead buttons. Within the envelope It, the grid leads are connected to the opposite ends of a helically formed grid structure 38 substantially encompassing the entire filament and including a support leg 39.

., ond of said walls, a pair of filament lead buttons The opposite wall 23 of the envelope I8 is pro- 1 those elements and occupying a position relatively close to the wall 2i of the envelope.

In addition to the mentioned parts, in the interior of the envelope, preferably on each of the lead buttons such as 28 and 29, and 36 and 31, as well as 4| and 42, sputter shields 41 are disposed. These are constituted of discs of suitable material forced over the leads as they emerge from the buttons to lie adjacent the interior surface of the envelope each in a location substantially intersecting all direct lines of communication from the filament to the envelope adjacent the respective lead button.

In the operation of this device, the interior of the envelope [8 is appropriately evacuated and the various lead connections are made so that the filament 33 is energized. The customary electron travel occurs and the gage is utilized in the usual Way to afford ion concentration readings. Especially important is the fact that emanations from the filament in the nature of small metallic particles which normally are conducting and which tend to coat the interior of the envelope and short circuit or cause leakage or drainage currents from the various conductors passing through the envelope, are substantially entirely intercepted. This is especially true near the open ends of the anode. While the sputter shields 41 may themselves eventually be coated with conducting material on the side toward the filament, the other side remains a good non-conductor. The sputter shields in effect shade or shadow the various lead buttons so that the interior of the envelope adjacent to the conducting parts of the lead buttons is kept free of on said first wall, a filament connected to said filament lead buttons extending across said envelope and resting on said support, a pair of grid lead buttons on said first wall, a grid connected to said grid lead buttons and encompassing said filament, and extending across said tubular connector, a pair of anode lead buttons on said second wall, an anode connected to said anode lead buttons and encompassing said grid, and disclike sputter shields on each of said lead buttons disposed parallel to said planar walls and out of contact with said envelope and shading said buttons from said filament.

2. An ion gage comprising a non-conducting envelope of drum shape having a pair of opposite planar walls and a tubular connector in the intervening cylindrical wall, filament and grid supports in one of said planar Walls, an anode support in the other of said planar walls, a filament and a grid on their respective supports within said envelope, a helical anode on said anode supports surrounding said filament and said grid and close to said cylindrical wall, and sputter shields on said supports adjacent both of the open ends of said anode and spaced from said envelope and interposed between said filament and the portions of said envelope carrying said supports.

FRANKLIN C. HURLBUT.

References Cited in the file of this patent UNITED STATES PATENTS

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