US2882429A - Gas measuring apparatus - Google Patents

Description

April 1 1959 ER 2,882,429

Unite States atent O dated Electrodynamics Corporafion, Pasadena, Calif., a corpomtion f California Application May 9, 1957, Serial N0. 658,206 6 Claims. (C1. 313 -7) This invention rela'te'as to elecitr0nic tubes, and m'ore particularly to a gas discharge tube Such as the cold cathade gas discharge tube use'd to measure gas pressures.

The invention i's dest'ribed herein as applied to a cold cathode discharge tube such as that described in Patent N0. 2745059 issued May 8, 1956, to R. C. Gauger. However, various featur'eQs of my improved device are applicable not only to cold :athode gas discharge tubes, laut also to other types cf g'as discharge tubes and in so'm'e respects to electronic tubes in general.

The cold cathode gas discharge deVice 'for mea'suring gaS pressures described in Patent N0. 2745059 includes an umbrella shield attached to a ceramic insultor disposed Within an e nvelope abo1'1t the lower pa'rt of a lead-in Wire to the anode. This umbrella shield satisfac'torily protects the body of the ceramic: insulator fro'm sp1'1ttered metallic material which could, after seine peri'0d cf 0;)- eration, bridge the insulato'r With a conductive-coating and cause the tube to becorne inoPerable. However, c0ating of the insulator with the sputtered material, even though it is not gre'at enough to bridge the insulator, may interfere with the proper operatit n of the tube after l'ong periods cf time. Thus, the metallic mterial rem0ved from the electrodes and depo'sited 011 the adjacent ceramic insulator may increase the eflective area of the an'ode, requiring a change of calibra'tio'n in the system in which the tube is utilized.

The present invention di'sclose's improvetnen'ts that 0Vercome the foregoing difficul'ty and also afford additional advantages in vaeuum tube construction. Thus, in accordance with my invention I Provide a tube ha'ving at least tw'o primary 'electr0des spaced ft0m each other in an envelope and an auXillary electrode having an orifice therein. A conductive lead to one of the electrodes, e.g. an anode, asses thr'ough the orifice but is spaeed froin the walls 'thereof by an annular gap, preferably n 1uch longer than it is wide. The auxiliary electrode it'self is coimected to another of the pri'rnaty electrodes, e.g. a cathode. Preferably the Width of the annular gap iS1e'ss than the spacing between the elecztrodes in the enVel0pe.

A cold cathode g'as disch'arge tube inc0rporating the improvement just described Will c0ntinue to co'nduct eurrent when the pres'sure of gas Within the tube rises to a high value, so that the cu'rrent flow through the tube can be sed to operatia external cirCuitr'y, e.g. a relay, 'when the higher pressure ptevails. By way o'f exar'nPle, a couventional cold ca'th0d'e discharg'e tube c'o'nducts Current Only when the pres'sure Within it is below about 25 'I-Ig. Above this pressure, discharge is extinguished. In contrast, such a cold ca'thode discha'rge tube modified to inclde the *auxiliary ele itrode a'rrangement just des'c'zfibed continues to operate as the press'u're rises to atrnospher'ic levels (760 mm. I-Ig), b'e'cause a's pressre is increased the discharge transfers to the anriular gap betw'een the-lead and the au'xili'a'ry electrode and continues to pass curre'nt in the fonn of an arc or spark.

In my preferred tube structure, the orifice or bore in the auxiliary electrode communicates with a chamber nutsid'e the env'elope olE the tula. Th'is chamber is sealed from the atmosphere. A cup-sha'ped in'slating bu'shing forms at least a part of the Wall cf this chamber and the conductive lead 'pas'ses through a seal in this c'up. In a cold cath0de dischafge tube modified to include the features just described, dischrge takes place between the primary electrodes in the -envelope While the tube is innetioning at low p'ressure. The mean free paths of the ious formed in the dist'zharge are so l'ong that the ions are unable to ass thrbugh the 'relatively long narr0W gap in the auxiliary ele'ctr0de. Hence, metallie deposits in the gap are minimized. At the Same time, the ct'1p-Sh'apied insl'1lat0r whi'ch forrns part -ot the Wall of the outside chamber is Prote'c'te'd from 'xh'etz'allic dep0sits. In consequence, n'o chan'e ot: ':rs in the efieetive electr0de =area to require a ehanjge in k;alibfatltm and the i'nsul'atlr is 151'0- tec'ted more effectively ftorn sho r't circu'its.

Ass'erhbly and -disassembly of tubes c'onstruded in accordamze with my inve'nti'on ar'e gre'atly fa'cilitated il5 the primary electtode, e.g. the an0de, the attaching l'ead, the auxiliarY elect'rode, and the t:up-shaped insulator form a unitary structure held in an electrode insert opening in the envelope, for ex-ati1ple by a threaded retainer.

These and other aspects o'f the ii1vention Will be urlderstood thor0ughly in the light of the f0llowin'g detailed de'scription f -a pr'e'sen'tl3? px'ferred embodiment. The description is ill'str'atecl by the aecompanying drawings, in which':

Fig. 1 is a 's'ecti0tizll elevational view showing a preferred embodiment of'nay neW invefi't'ion in a cold cth0de ga"s discharge device; and

Fig. 2 is a fragmentary sectional view taken along line 2- 2 of Flg. 1.

The drawings Show a cold cthode discharge tube 10 provided With an elong'a'ted e'fivtelope 12 of condu'ctive materil. This envelope has a gas inlet 14 formed at on'e and thereof, ptarrnitti'ng the gas di'sch'a'rge tube to be attached to a gas pie'ssure source (not shown).

' The tube has a fir's't (:ath '3de 16 and a second c'athode 18 diametric'ally disposed 'Within the Wall of the 'C0nductive envelope 12. Disp0sed in the space between the two cathodes and along the aXis of the conductive envelbpe i's an anode 20. This 'anode is in the form cf a loop. The cathodes are tapered toWa'rd the ar'1ode and have plane surfaces 16A, 18A sub'stantially patallel 'with the plane of "the 10013 a11o'de (see Fig. 2).

When gases enter the area within the envel'ope, elactrous from the cath'odes are atttact'ed t0ward the an0de. As they pr0eeed toWa'rd the anode collislonS With the g'as rholecules oc'cr, ptoVidi'ng pbsitive ion's which the11 flow to'ward the c'ath'odtas. The l1'1'gel the path foll0wed by the electrons frofn the c'a'thodies, the rnore chance of collision With gas molecul'es. T0 in'cre'a'se the path cf the electrons from the cathodes to the anode, a magnet 22 cf substantially annular shape is disposed adjacent the cathodes. The field produced hy the m'agnet tends to direct the electrons from the cathodes a'wa'y from the anode. This causes the 'el'et'rorx's to follow a helical path to the anode. -As the path 0'f the electron's is thus inerea'sed, there is opportunity for 'mri: collisio'm With the gas molec'ul'es.

An insulator housi1'1g 24 'of flexible rubber encl'osiz's the cath'odes, the magnet, anti an annular stiffener 26.

The lower portion cf the cbnductive enVelope is provided With a bor'e 28 'of fed'uctd diar'n'eter. This bte is sufliciently large 'to 15ermit the ins'er'tioh and rem0val of the anode from the env'elope.

A conductive bushing or zixiliary 'ele'etrode 30 is releasably clarnped to the lower p0'rtion of the envelope. This bushing is of a substantially cylindtical shap'e and ineludes a hub portion 32 which extends into the bare. A long narrow orifice extends entirely through the body and hub portion cf theconductive bushing. This orifice is cf larger diameter than a conductive lead 34 which extends through the orifice and is connected to and suppcn:ts the anode. Thus there is an annular gap 36 separatmg the wall of the .ori fice from the conductive lead. The conductive lead is in sealed connection with an 1nSulator 38. This insulator is cup-shaped. Its upper um is connected to a conductive sleeve 40, which in turn s connected to the lower portion ofthe conductive bushmg. The bushing, sleeve and insulator thus define an aux1 liaxy chamber 42. A by-pass bare 44 in the bushing connects the interior of the envelope With the auxiliary chamber and aids in pumping out the latter.

In the structure just descrbed, the cup-shaped insulator 1s eutside the envelope 12 and metallic materials resultmg from sputtel'ing will not be cleposited on it.

The anode, leadcup-shaped insulator 38, conductive sleeve and conductive bushing are connected together in a nnltary structure and cqnstitute the anode assembly. Th1s may be removed as a unit for examination and repair. T this end, the lower encl of fl1e envelope is threaded to accommodate a threaded cup-shaped retainer 46. 'I'here is a hole 48 in the bottom of the retainer. The diameter of the hole is greater than the diameter cf the cup-shaped insulator 38 but less than the diameter of conductive bushing. Hence, the retainer may be unscrewed and removed over the insulator. The anode as sembly can then be removed.

Conversely, the anode assembly is replaced by inserting the anode and plaeing a locating pin 50 in a recess formed m the conductive bushing. The retainer is then replaced over the insulator 38 and screwed upon the envelope, with the lower portion of the retainer pressing against the conductive bushing. A gasket 52 is located in a groove formed in the envelope to provide for seal-tight engagement.

In operation, when the tube is functioning at low pressures, it continues to conduct current by ionization of.the gases within the envelope. The ionization takes place primarily in the space between the cathodes and the anode. As the pressure is increased, the discharge transfers to the gap between the conduetive bushing and the lead continues to pass current in the form of an arc or spark. 'I'he improved model will continue to operate up to atmospheric pressure, thus permitting the use of the tnbes in applications where an auxiliary relay is used to operate external circuitry at some level above a chosen pressure limit.

When discharge takes place in the space surrounding the anode loop during Operation at low pressures, some ions tend to travel to the inside surfaces of the envelope, but are unable to ass throngh the relatively long gap in the conductive bushing. Thus, metallic deposits an the cup-shaped insulator are reduced to a minimum. When operated at higher pressures, so that the conductive bushing operates as an auxiliary electrode, the mean free paths of the ions an: so small that ions are again unable to mach the surface cf the insulator 38.

I claim:

1. In an apparatus for measuring gases the combination comprising an envelope defining a gas discharge space, first and second primary electrodes, means for snpporting the second electrode within the envelope, insulating means secured between one end cf the envelope and the first electrode for supporting the first electrode within the envelope and in spaced relation to the second electrode, an auxiliary discharge electrode surrounding at least a portion of the first electrode and disposed between the insulating means and tl1e gas discharge space, the auxilia.ry electxode being electrlcally coupled to tl1e second electrode and being radially spaced frorn the first electrode to impede the movernent of ions in a substantially annular gap formed between the first and auxiliary electrodes to thereby substantially prevent ions from the gas discharge space from reaching the insulating 4 means and producing a metallic deposit on the insulating means.

2. In an electronic device for measuring gases including an envelope defining a gas discharge space, first and second primary electrodes and means for supporting said electrodes within said envelope, the means for supporting the first electrode including insulating means secured between one end of theenvelope and the first electrode, the improvement comprising an auxiliary electrode providing an arc discharge path for said first electrode including electrically conductive means substantially surrounding a portion of said first electrode and disposed between the insulating means and the gas discharge space, the auxiliary electrode being spaced from said first electrode to form a long and narrow annular an: gap impeding the movement of ions through said gap to thereby substantially prevent ions from the gas discharge space from reaching the insulating means.

3. In a gas discharge device for measuring the pressure of gases including an envelope defining a gas discha1ge space, an anode, a cathode and means for supporting said anode and cathode in spaced relation to provide for gas discharge at low gas pressures, the improvement comprising an auxiliary discharge electrode annularly disposed abont a portion 0f said anode and proximate thereto for producing an a1c discharge at higher gas pressures extinguishing the gas discharge between the anode and cathode.

4. In gas discharge devices for measuring the pressure of gases including an envelope defining a gas discharge space, and means producing a discharge in said space including an anode and cathode and means for supporting said anode and cathode in spaced relation within said envelope, the means for supporting the anode including insulating means secured between one end of the envelope and the anode, the improvement comprising arc discharge means including an annnlar auxiliary electrode connected to said cathode and disposed between th e insulating means and the gas discharge space, the auxiliary electrode being spaced radially about a portion of said anode to provide an arc gap between said anode and auxiliary electrode which is less than the space between said anode and cathode to thereby substantially prevent ions from the gas discharge space from reaching the insulating means.

5. In gas discharge devices for measnring the properties of gases inclnding an envelope defining the gas discharge area and first and second primary electrodes of opposite polarities snpporting within said envelope, the improvement comprising arc discharge means for measuring properties of gases outside the range of gas discharge including an anxiliary electrode connected to said second electrode, said auxiliary electrode substantially surrounding a portion of said first electrode and spaced radially therefrom to provide an arc gap between the first and auxiliary electl'odes which is smaller tl1an the mean f1ee path cf ions formed in the gas discharge area, and annular enclosure means secured to the auxiliary and first electrode to provide a sealed chamber outside of said envelope opening into said arc gap, said enclosure means being formed at least partially of material insulating said first electrode from said auxiliary electl'ode.

6. In a cold cathode gas discharge tube for measuring properties of gases at low pressures including an elengated envelope having at least one open end and defining the gas discharge area, an anode, a pair of cathodes, and means for supporting said cathodes on diametrically opposite sides of said envelope, the improvement comprising an: discharge means for continuing conduction at gas pressures snstaining gaseons discharge including an annular auxiliary electrode having an aperture connected to at least one cathode and disposed at one end of said envelope, said electrode snrrounding a portion of said anode and spaced radially from said portion to form a lang narrow annular an: gap blocking assage of ions through said gap, means for forming a sealed enclosure seating against transverse edges of said auxiliary electrode, and a clamping portion releasably securing to the adjacent lateral sides of the open end of said envelope.

References Cited in the file of this patent UNITED STATES PATENTS Gauger May 8, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,882429 April +y 1959 Boy G Gauger appears in the prinued specification I'b is hereby certified thao error correcnion and than bhe said Letters of the' above numbered patent requiring Patent should read as corrected below.

Oolumn 4, line 48 for "supporting read supportad Sigriad anci sealed 11113 um .day of August 1959,

(SEAL) Attest:

KARL H. AXLINE Aiia*sng Officer ROBERT C. WATSON Commissioner of Patentsv

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