US2367570A - Electric tube - Google Patents

Description

3am 1% 19 35 u FUNARQFF 2,357,570

ELECTRIC TUBE Filed July 8, 1943 49 INVENTOR [g v .50 4' 4 6 J1 ATTORNEY tioned with an electrode lace area or electric resistance is virtually not Patented Jan. 16, 1945 ELECTRIC TUBE Urie Funaroif, Bloomfield, N. J assignor to Westinghouse Electric East Pittsburgh, vania & Manufacturing Company, Pa.', a corporation of Pennsyl- Application July 8, 1943, Serial No. 493,887

Claims.

This invention relates to electric devices for measuring, receiving, amplifying or control purposes in general, and in one of its more particular aspects to measuring tubes or pressure gauges of the Pirani type.

In Pirani gauges, a vessel or tube envelope having a conduit for supplying the pressure to be determined contains an electrode or conductor filament which is exposed to the tube atmosphere and, when in operation, is traversed and heated by electric current. The resistance of the electrode or filament varies in dependence upon the dissipation of heat through the tube atmosphere. Since this diss'pation is dependent upon the gas pressure, the resistance of the filament is a measure of the pressure magnitude to, be

determined.

For accuracy and high speed of response, it is often desirable to use in such and other electric devices an-electrode or conductive filament which offers maximum surface and maximum electrical limited by the prior "art dimensional requirements imposed by the necessary mechanical strength,

V stability and ruggedness of construction.

An object, allied to the-foregoing, is to provide such a device with an electrode or filament which contains a large efiective surface area and a high resistance together with high mechanical strength and stability and at a minimum of thickness and thermal mass. According to the prior art, some of these desirable characteristics appear contradictory. In particular, the available surface area, electrical resistance, minimum thickness and minimum mass have heretofore been limited by the need for suflicient mechanical strength and ruggedness of construction. Another limiting factor in measuring and control devices of this kind, especially in previous gauges of the Pirani type. has been the necessity of maintaining a constant characteristic and a coristant zero point of the electrode or filament circuit. As a result, the known Pirani gauges have had a rather limited accuracy, have been nonuniform and have possessed a relatively high time constant oi response. p

In one of the known Pirani gauges, the filament is composed of a core wire of a mechanically strong butchemically active metal, such as tantalum, with a coating of a mechanically less resistant but chemically inert metal, such as platinum. However, the maximum surface and the maximum pressure or temperature-responsive resistance of such a coated metal filament are also limited by the lowest permissible strength and size of the conducting metal core, and the core metal. is apt to oxidize below the coating. especially at high temperature.

It is an object of the present invention to' provide an electric device of the types aforemenor filament whose surmeans. The coating may be made of platinum,

total electrical resistance together with high mechanical strength in proportional degrees not obtainable with the known tube and filament constructions.

Another object-of the invention is to provide an electrode or filament in measuring tubes, for instance of the Pirani gauge type, which ofiers an increased sensitivity and speed of response in conjunction with'astable characteristic and zero point.

A further object related to the one just mentioned is to increase the effective surface area of a tube electrode .or filament while maintaining a high total electrical resistance and a high e1ectricaland mechanical stability.

According to the invention and for achieving the foregoing objects, the active electrode or filament of an electric device as above characteriz'ed is composed of a body or base of insulating material and a coating disposed on the insulating body and consisting of the active conductive material. The insulating body consists preferably of a material capable of withstanding the operating temperature of the conductive coating without appreciably afiecting the characteristic of the filament. Heat-resistant or highly refractory inorganic substancessuch as mica, alundum, lava, and quartz are especially suitable for this purpose, although glass and glass wool ribbons can also be used at most operating temperatures.

The conducting coating or film is'secured to the surface of the insulator by sputtering, spraying, electroplating, mirrorplating or other suitable iridium, or other material suitable for Pirani gauges or other electric vacuum tubes. Its resistance is adjusted to suit the desired purpose or characteristics by omitting, scratching or cutting away parts of the surface film as well as by properly selecting the thickness of the film or coating.

To secure maximum surface and minimum thermal. mass of the insulating base, said base may be made in fiat sheets, fine strands, threads or ribbons, arranged, corrugated, spiralled, wound as a helix, folded in accordion shape or otherwise, and mounted or connected in multiple or seriesunits if desired. The invention will be more fully understood filaments or electrodes for electric devices according to the invention; and

Fig. 8 is a perspective and partly sectional view of a resistor arrangement for measuring determinants of fluid flow, the measuring resistors consisting of filaments or electrodes as disclosed by this invention.

Referring to Fig. 1, reference numeral I indicates the envelope of a Pirani measuring tube. The envelope is attached at its lower end to a base 2 and at its upper end is shown as-having a tubular conduit 3 for supplying the atmosphere whose pressure is to be measured. The envelope I, while indicated as comprised of glass, may be of metal, or other material, and preferably has a substantially cylindrical, elongated shape. .Its axial-end, for convenience denominated as the lower end and opposite to the supply conduit 3,

likewise for convenience of description referred to as the upper'end, is formed with a reentrant stem and press 4. A central holder 5, preferably comprised of a glass rod, is mounted on the press 4 and extends upwardly therefrom coaxial with the envelope. A plurality of arms, here shown as four in number, 6, I, 8 and 9, radiate from and are carried by the holder next its upper end, said arms being disposed at right, angles to one another and in a common plane transverse to the holder. These arms serve to secure the electrode or filament sections in proper position.

Two lead-in wires III and II from outside terminals I2, II at the underface of the base, extend upwardly within the press 4 and project above the press on opposite sides of the holder. The electrode or filament structure-is suspended from said radial arms and-comprises as many sections as there are arms. The present showing provides four sections marked II, II, "and I1, respectiv'ely. A bottom marginal portion of one section I4 has a connector ll applied on one face of the said section and a bottom marginal portion of a next adjacent section I! has a connector Is one face of said adjacent section looking toward the first said face. These connectors I8 and I! are welded, soldered, or otherwise securadzto upper ends of said leads I II and I I.

It is desired to provide a long path for the current traversing the filament from one lead-in wire'- to the other. Understanding ofaccomplishment of this desideratum will follow more readily from a description of the filament structure. Generally speaking, each of the opposite faces of each section is an electrically conductive surface distinct from. the eiectricalconductiye surface on the other face of the section: Each filament-section consists of an insulating body or base 20 which is preferably in the form of a strip or sheet according to Fig. 3, and which is covered on opposite faces, but not around the edges, by a varistor coating of conductive material, thereby providing each filament section with filament portions 2|, 22 on opposite faces of the body 20. The coating material consists of electronically or electrically effective substance and may be applied by dipping, sputtering, spraying, painting, lating, or other acceptable manner. In a'Pirani gauge, as illustrated in Fig. 1, a, chemically inert metal, such as platinum, iridium or an alloy thereof, is preferably applied as the varistor coating. It will be understood by those skilled in the art that a varistor material is'one which has a change of characteristic, usually a resistance characteristic resultant from being exposed to heat, light, pres sure or other condition. Since the electrode or filament of the specific structure being described should withstand relatively high temperatures, the non-conducting base 20 is preferably made of a refractory material such as mica, steatite, lava, alundum, or quartz.

In order to prolong the electric path of the filament surface, filament portions or coatings 2I and 22 are omitted, Scratched, or cut away at appropriate locations for the purpose. For instance, filament surface separation is shown lc-ngitudinal of the filament section intermediate of the side edges from the bottom and up'to a short distance from the top of the section so that narrow strips 23 and 24 on both margins of the filament body are free of conducting'material and bisect the conductive surface for most of its length. As a result, each filament section forms a conducting path on the faces thereof having the general form of an inverted U, by which the conducting path extends upward at one longitudinal margin of the surface of the insulating body, crosses to the opposite margin and then proceeds downward at the said opposite margin to the bottom end thereof, thus resulting in an effective double length of path of about double the length of the body on one face of the body. A like double-length of path is provided on the other face of said section. For convenience in reference, the filament area on the margin nearest the structure supporting post or holder 5 will be referred to as the inner leg of the filament portion and the area on the far side of the nonconductive strip more distant, from the said post will betermed the outer leg of the filament These two leg areas connect at their upper ends by an area which will b referred to asthe file ment hip.

The bottom of the outer filament leg on one face of the insulating body is'connected to the bottom of. the outer filament leg on the opposite face of said body by means of a u-shaped clip 25, or other means, passing under the end of said body from the leg of one filament portion to the corresponding leg of the other filament portion.

' The inner filament legs, however, each preferably'have individual strip-like connectors of which two, identified by numerals I8 and I9 have been referred to above, and the others of which are now identified by numeral 26. There is no direct connection between the connector on one face of the insulator body with the con- *nector on the reverse face thereof, but the connector 26 on one insulating body is ioinedwith the next succeeding connector on the next insulating body, by means of a conductor 21 shown in Fig. 2 asl a short wire bent at a right angle and situated with its legs cross-wise of the filament and longitudinally of the connector, and sel the exterior terminal I2 through lead III cured thereto by welding or otherwise. Consequently, an electric current path extends from nector I8, thence upthe inner leg, across the "hip and down the outer leg of filament portion 2| of filament'portion I4, nector 25 under and to t hence by way of cone opposite face of the to consulating body insulating body; up the outer leg and down the inner leg of that portion l of the same section l4, thence over conductor 21 to the next section l4, through the full length of filament portions 2|, 22 on opposite sides of that section, and similarly to and through successive conductors 21 and sections the full length of filament portions 2|, 22 thereof, and then to the lead H and the exterior terminal I3. a

In order that the several filament sections may be supported at theirupper ends-without shortcircuiting from portion 2| thereof on one face of the body' to the portion 22 o the other'face the body is freeeof filament coating or material for a marginal depth 28 and suitable clips 29 are ap-. plied at those margins adequately secured, as by gripping and frictional engagement of the in- Tabs or ears 3!! stamped from these clips form a means by which the clips may be welded or otherwise secured to the arms 6, I, 8

and 9.

In operation, an electric measuring circuit is connected to the terminals 12 and I3 so as to measure either the resistance of the above-described current path or the voltage or. current in the measuring circuit as determined by the resistance magnitude of this path. Due to its connection at 3 with an atmosphere, for instance, a low vacuum tobe measured, the dissipation of heat from the sixteen filament legs of the eight filament portions of the four filament sections of the electrode through the inner tube atmosphere depends on the thermal conductivity of the tube atmosphere and hence on the pressure to be determined. As a' result, the measured magnitude of the gauge resistance, voltage or current is a measure of the pressure magnitude. specific number of sections, portions and legs have been shown and recited for clarity, it is to be understood in practice that the number may be otherwise as found desirable or necessary.

The modification of an, electrode or filament arrangement illustrated in Fig. 4 is of the selfsupporting type. The electrode consists of a thin cylindric sleeve 29 of insulating material whose inner and outer surfaces are covered byconducting filamentary varistor coatings or portions 30 and 3|, respectively. When using this structure in a Pirani gauge, the coating consists of platinum or the like chemically inert metal as heretofore mentioned. By omitting or cutting away part of the coating along a helical line so as to form a non-conductive path, each portion is divided into a winding of conducting material. A terminal or lead 32 is attached to the lower end of the outside conducting strip or portion'3l, and another lead v33 is attached to the lower end of the inside conductive strip or portion. .A connector 33 is applied over the upper edge of the electrode structure so as to electrically connect the upper convolutions of the windings of the filament portions 30,- 3|.

The two'leadsj l and 33also constitute mounting means for the selfe supporting electrode structure. It will be seen that in an electrode or filament construction of this type, the electric current passes in series first through the entire length of one helical portion thereof, thence through the connector to the other helical portion and through the entire length of the last-mentioned helical portion.- The 'top and bottom edges of the insulating body are "free of conductive 'material seas to avoid, short- .circuitlngthereat. v I

According to the embodimentpf Fig.- 5 which While a a is also of the self-supporting type, a substantially helical insulating body or strip 34 is-covered at one or both surfaces with conducting and electrically effective varistor material and is attached 5 to two leads and mounting means 35 and 36,. so

that the electric measuring or heating current passes from lead 35 through the entire length of the coating on strip 34 to the other lead 36. Since the leads 3s, as are shown attached to the inner surface portion of the helically wound strip, the current passes through that portion. To also use the outer surface portion, the filamentary material is also appliedaround the edges of the strip or the ends thereof.

The embodiment shown in Fig. 6 contains an accordion-shaped strip or body member 34' of insulating material which is coated on one or both sideswith a temperature-responsive or otherwise electrically effective varistor material of the type and for the purposes above described. The strip (or body 34 is attached to lead wires 35' and 36, which serve also as mounting means for connecting the coating with a measuring or operating circuit. Here again, for use of both surface portions of the filament material, the said material is applied around the ends of the strip or around the side edges or otherwise as found most expedient or desirable.

metallic filamentary varistor coating is applied to a rectangular flat plate or body- 31 of n0n-con ducting material. The coating consists of a metallic film or deposit so arranged as to extend in the following manner.- The conductive path begins at a metal connector 38 attached to a lead wire and mounting means 39 and extends upward along an upwardly extending strip or filament portion 40. At the upper end, the filament portion 40 is connected over the,upper edge of 40 the insulating base with a similar strip or portion of coating located at the rear surface of the plate 31" and depending tothe bottom of said base to constitute a filament section. Another conducting filament section 4| extends likewise over both the front and rear surfaces of the base or plate 31, the rear and lower ends of said sections having ahip connection, whereas the lower front end of said second section 4! has a hip connection 42 with a third conducting section 43 similar to the first one 40. The upper end of section 43 has a connector 44 attached thereto which in turn is attached to a central lead and holder 45. The lower rear end of section 43 has a hip connection with the lower rear end of a fourth see-- as tion whose lower front end has a hip connection 41 with a fifth conducting section 48. The lower I rear end of section 48 has a connector 49 attached thereto which in turn is connected to a lead and'supporting means 50. -The three leads 0 and supporting means 39; 45 and 50 are mounted on the stem portion 5I of a tube envelope similar to the stem 4 and envelope I shown in Fig. 1. By appropriate circuit connections 52, 53 and 54 from leads 39, 45 and 50 respectively through a special double-blade switch 55, '56, current from a supply line 51, 58 may be passed as desired in series through the several filament sections or in parallel through the two halves thereof.

When-the leads 39,;45 and Silare properly connected to an electriclieating and measuring circuit, represented by supply lines 51, 58 as with the switch blades in dotted linerposition, the cur- 6 rent flows from lead 45 through one-half of the filament sections to lead 39, and also through the 7 other hair of. the filament sections to lead 50.

pressur ranges or sensitivity, etc.

The operation of the electrode constructions shown in Figs. 4 through '7, when applied to a Pirani gauge, is in principle similar to the abovedescribed operation of the tube shown in Fig. 1.

The main advantage of such plated-insulators over the known filaments is that the maximum" various electronic tubes. For example, in a photoelectric cell or photo-glow tube, a metal of high surface resistance or thinness are no longer limited by the strength of the conducting material, but can be made as large as the size of the tube permits and as thin as feasible. The fact that conducting varistor materialcan be deposited by piatinir. spraying, and otherwise, permits making the filament about 10 to 100 times thinner than previously possible and, thus for a given surface area for the filament per unit of length of current path, as well as by permitting use of increased filament length, affords greater resistance in the same tube space or unit volume than was previously possible.

Other advantages of such filaments are that 'a weak conducting material can be used without any danger that a force acting on it tends to stretch or break the filament proper or make it sag and change in length'and resistance. The conducting filament unit is also prevented from changes caused by its own weight. By virtue of these propertieahigher flashing, baking and operating temperatures can be,used. As a result,

the filament is degassed more thoroughly and quickly and assumes more uniform and desirable characteristics, without dangerously weakening or injuring the filament structure or shortening the life of the tube, an achievement not attainable by prior art constructions. Moreover, the filament or electrode retains this uniformity and initial characteristic for a much longer time. The large surface can be fixed veryaccurately merely by keeping the easily measurable overall large dimensions of the insulator very accurate without being affected appreciably by variations in thickness of either conducting or insulator material. The initial resistance can easily be kept within limits of accuracy of the measuringinstruments used, by scratching lines in the conducting surface until the desired resistance is obtained, or by controlling the'conductor's thickness or resistance in any other suitable manner. Thelarge magnitudes of surface and resistance possible with such coated filaments renders non-uniformities in the manner of attaching, clamping, or welding supports. clamps and leads, and variations in the size or thickness of these auxiliary elements relatively smaller so that the magnitude of such non-uniformities becomes as a rule negligible. These advantages and the absence of fragile materials facilitate manufacturing these articles in accordance with desired initial characteristics and with much greater accuracy, higher degree of uniformity, and much. less shrinkage than hitherto possible. This also reduces or eliminates the requirements of calibrating each tube or matching pairsoftubes.

Such plated or otherwise coated insulator-filaments also lend themselveslrfiore readily to other uses, such as directly heated large-surfaced hot cathodes, anodes or electron-emitting plates in work function but better physical characteristics as to permanence, destructibility, or volatility, than potassium or other usual metals, can be used if plated on an insulating base and heated by an auxiliary filament current to a point where the energy or work, necessary to pull an electron out of the plate, is decreased by the raised temperature to the desired operating value or voltage.

Fig. 8 represents a case in which the invention is applied to a pair of temperature-responsive resistors for measuring a rate of cooling or rate of flow. The resistors consist of substantially U-shaped strips 'II and 12, each containing an insulating base coated with thermo-responsive resistance varistor material. The strips are arranged in substantially the same plane fill .the past.

within a tube II which forms part of a conduit system for conducting a fluid stream whose rate of flow or rate of cooling or heating is to be measured. The location of the resistors is substantially central to the flow lines so that the fluid passes first along one and then along the other resistor affecting their respective resistance r values in dependence upon the local temperature or thermal conductivity of the fiuid. Each resistor is. attached to a pair of terminals", II and l, 11, respectively,-for connecting them to -a measuring circuit (not shown) in order to desible to measure very small differences in temperature or thermal conductivity and hence permits placing the two resistors much closer togetherthan heretofore possible. As a result, the

invention in this aspect leads to simplified and specially condensed measuring apparatus. For instance, it is possibleby virtue of the invention to place both theme-responsive resistance elements into a single enclosure as shown in Fig. 2, rather than using two separate Pirani-type elements for this purpose as has been necessary in In fact any filament similar to those shown in Figures 1 thru 7 can be arranged for flow measurements by simply placing them axially parallel to the stream fiow and calibrating the instrument with known rates of fiow or by dividing into two halves placed and connected in a manner similar to that explained for Fig. 8. The invention is adaptable to measurement of variations in the surroundingmedium such as ay be due to temperature, light intensity, mechanical or gas pressure, or changes in composition, in that a coating may be chosen whose resistance varies with changes in any or all of these conditions. I

While I have described in detail a limited number of embodiments in order to exemplify the invention, it will be understood by those skilled in the art that the invention is not limited to those embodiments but may also be carried out in various other ways without departing from the above-mentioned objects and advantages and within the scope of the invention as set forth in the appended claimb.

I claim: l 1. A gauge electrode subiect to variation in conductivity by the character of the pressure of fluid medium surrounding the same and in contact therewith, comprising an insulative self-susi a film-like electrically conductive material on said body, said material forming a continuous and highly resistive electrical path and changeable in its resistance by effects of the pressure of fluid medium surrounding the same and in contact therewith, and means for connecting a test circuit to said electrically conduc tive material at parts thereof electrically remote from each other.

2. A gauge electrode subject to variation in conductivity by the character of the pressure of fluid medium surrounding the same and in contact therewith, comprising an insulative self-susraining body of large surface area-compact within a small space, a film-like electrically conductive material on said surface area and establishing a long and devious electrical path within said small'space, said material being electrically re sistive and subject to heating by passage of current therethrough and having its resistance changed by change in the pressure of fluid me dium surrounding the same and in contact there= with, and. means for connecting a test circuit to said material at parts thereof electrically remote,

to each other along said devious electrical path. 3. A Pirani pressure gauge, comprising an en velope having duct means for supplying a gas pressure to be measured, a measuring conductor disposed in said envelope to be exposed to said pressure, and leads passing through said envelope to supply current from the outside to said conductor, said conductor having a heat-resistant insulating section and a conductive film dis-" posed on said section and connected with said leads.

4. A Pirani pressure gauge, comprising an envelope having duct means for'supplying a. gas pressure to be measured, a section of insulating material arranged in said envelope and having a plurality of adjacent portions so as to cover a surface area of multiple width as compared with that of a single section, a conductive coating of chemically inert material deposited on said insulating section within the envelope where exposed to the gas pressure from said duct, and leads passing through said envelope and connected with said coating for supplying current thereto.

5. A Pirani prewire gauge, comprising an envelope having duct means for supplying a gas pressure to be measured, an insulating body of heat resistant material arranged in said envelope, a conductive coating of chemically inert material deposited on said insulating body within the envelope where exposed to the gas Dressure from said duct, and leads passing through said envelope and connected with said coating for supplying current thereto.

- URIE FUNAROFF.

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