US3370195A

US3370195A - Cold cathode gas discharge tubes having an optically opaque masking plate

Info

Publication number: US3370195A
Application number: US495239A
Authority: US
Inventors: Stenning George Peter
Original assignee: Hivac Ltd
Current assignee: Hivac Ltd
Priority date: 1964-10-16
Filing date: 1965-10-12
Publication date: 1968-02-20
Anticipated expiration: 1985-02-20
Also published as: NL6513368A

Description

3,37%,195 Patented Feb. 20, 1968 3,370,195 COLD CATHODE GAS DISCHARGE TUBES HAVING AN OPTICALLY OPAQUE MASK- ING PLATE George Peter Stenning, Stanrnore, England, assignor to Hivac Limited, South Ruislip, Middlesex, England, a British company Filed Get. 12, 1965, Ser. No. 495,239 Claims priority, application Great Britain, Oct. 16, 1964, 42,349/64 4 Claims. (Cl. 313-204) ABSTRACT 01? THE DISCLOSURE Cold cathode gas discharge indicator tube having several shaped cathode electrodes in front of at least one of which is an optically opaque masking plate provided with a light-transmitting aperture therein to permit visual observation of only those parts of the glow discharge on such cathode electrode which provide the required shape of visual indication.

This invention relates to cold cathode gas discharge tubes and is more particularly concerned with devices, commonly referred to as indicator tubes, in which a plurality of separate cathode electrodes, in stacked relationship, are provided with individual external electrical connections thereto for selective cooperation with a common anode each cathode electrode being of different shape and so arranged as to provide a variety of visual glow discharge displays having the respective forms of different characters such as letters, numerals, algebraic signs, and the like.

In the construction of such tubes it is necessary to support each of the alternative character electrodes in a separately insulated manner and this is usually effected by providing each electrode with two or more outwardly directed extensions or lugs which serve as anchorage points for mounting each of the characters of the stack upon spaced apart support rods disposed normal to the respective planes of the different electrodes and located just outside the boundary of the viewing area in which each of the different discharge displays occurs. Such support rods are usually located at opposite sides of the stack, e.g. one above and the other below in the vertical median plane of the stack when the electrode planes are vertical.

While such disposition is the most convenient for most numerals and many alphabetical characters, such as B, C, D, E, G, I, O, Q, S, T, and Z owing to the existence of regions of the required character shape immediately adjacent the anchorage points, certain other characters such as H, J, K, L, M, N, P, R, U, V, W, X and Y present difficulties and need the use of one or more extensions to connect the character-shaped portion of the electrode to one or both of the anchorage points. It is clearly most important that such extensions should not glow and special measures need to be taken to prevent any glow discharge thereon such as by covering them with a layer of insulation. A particularly difficult electrode shaping to provide is one in which the required display isconcentrated in the mid region between the various support rods, for example, an algebraic minus sign and one object of the invention is the provision of an improved form of indicator tube construction for displaying such character shapings.

In accordance with one aspect of this invention a cold cathode gas discharge tube comprises an anode electrode, a cathode electrode arranged to provide a visual glow display and comprising a first component part shaped in accordance with the required display and one or more further parts extending therefrom to fixed anchorage points, and an opaque masking plate disposed in front of said cathode electrode and having an aperture therein shaped to allow visual observation of the glow discharge on said first component part when viewed in the normal tube viewing direction.

In certain applications of such indicator tubes, such as in connection with electronic computers, it is frequently necessary or is very desirable that a substantially constant value of glow discharge current flow be maintained in an associated circuit regardless of whether or not any one of the character-shaped cathode electrodes is being actively used to provide a visual indication. Hitherto in such case it has been the practice to provide a separate glow discharge tube having broadly similar current and voltage characteristics and arranged in an alternative circuit path which is switched into operation whenever the indicator tube itself is not required to provide a visual indication. Such arrangement has certain disadvantages, firstly, the need to provide a second discharge tube and, secondly, the need, at least approximately, to match the characteristics of the second tube to those of the indicator tube. Even with such initial matching balanced operating conditions will probably not be maintained over a prolonged period of time owing to differences of tube construction, and the different integrated usage of the two tubes.

In accordance with a second aspect of the invention a cold cathode gas discharge tube comprises an anode electrode, at least one display cathode electrode arranged to provide a visual glow display and an additional cathode electrode the glow from which is totally obscured by an opaque masking plate, the area of said additional cathode over which discharge takes place being substantially equal to the corresponding area of said display cathode or to the average of the corresponding areas of said display cathodes.

In order that the above and other features of the invention may be more readily understood one particular embodiment thereof will now be briefly described with reference to the accompanying drawing in which:

FIGURE 1 is a perspective View of a gas discharge tube according to one embodiment of the invention; and

FIGURE 2 is a vertical section of part of the electrode structure of the tube shown in FIGURE 1 taken along a line just inside the anode enclosure, part of the anode electrode being omitted for the sake of clarity.

Referring to the drawings, 10 indicates a tubular glass envelope containing a suitable low pressure gas filling. Within this envelope is arranged a first character cathode electrode 11 in the form of an algebraic plus sign constituted by a cruciform thin wire element anchored at the upper and lower extremities of its vertical limb 12 to horizontal

fixed supports

13, 14 forming part of a support structure (not otherwise shown) extending from the lower end of the tube. It will be understood that, in the usual way, suitable insulation, e.g. in the form of ceramic bushes 15, is provided at each anchorage point. Immediately behind the said first cathode electrode is disposed a vertical sheet metal mask plate 16 having a horizontal slot 17 therein. Immediately behind this mask plate 16 is disposed a further cathode electrode 18 again of cruciform shape similar and preferably identical with that of the aforesaid electrode 11. This second electrode is disposed with its horizontal portion 19 in alignment with the slot 17 when the tube is viewed in the normal viewing direction indicated by the arrow a. Behind the second cathode electrode 18 is disposed another mask plate 20 which is wholly opaque and behind this is disposed a third cathode electrode 21. This third cathode electrode should have the same surface area as each of the other cathode electrodes and may, for convenience of manufacture, be identical in form with that of the other two. This third electrode 21 is likewise anchored at its upper and lower ends to the

horizontal supports

13, 14 by way of insulating bushes or the like. The assembly is surrounded on three sides at least by a box-like anode structure 22 and the front, open end of the latter may itself be covered by a fine wire mesh 23 (not shown in FIGURE 2) which permits viewing of any glow discharge on the first or second electrodes therethrough. The

mask plates

16, 20 are preferably also connected electrically to the anode structure and form part thereof.

Leads

24, 25, 26 are connected respectively to the

separate cathode electrodes

11, 18 and 21 respectively while lead 27 is connected to the common anode.

In operation when the first electrode 11 is energised as a cathode for cooperation with the anode, the full cruciform or plus sign shape of visible display will be provided. When the second cathode electrode 18 is energised instead, although a cruciform glow discharge will again occur, only the horizontal limb 19 thereof will be visible through the slot .17 in the mask plate 16 thereby providing a minus sign indication. Preferably such horizontal limb and the aligned slot 17 in the mask plate are slightly displaced upwardly or downwardly with respect to the horizontal limb of the front electrode 11 to prevent any obscuring by the latter of the glow discharge when the second electrode 18 is energised. To facilitate manufacture using identical electrode shapes the horizontal limb may be placed slightly off-centre of the vertical limb and one electrode inverted relative to the other.

With the third electrode 21 energised, while a further flow discharge of cruciform shape will again occur, none of this will be visible and the tube is, outwardly, in the state providing no visualindication at all. Such third discharge, however, will have substantially the same I electrical characteristics as either of those of the first two and accordingly provides a discharge which is substantially balanced as regards its voltage and current requirements with those of the other two discharges. Furthermore, as the third electrode is itself located in the same gas discharge space its characteristics will tend to alter correspondingly with those of the first two and the balanced condition will be maintained throughout the life of the tube.

While the invention has been described in detail with relation to the provision of and signs its manner of application to other character forms will be obvious.

I claim:

1. A cold cathode gas discharge tube comprising an anode electrode, at least one display cathode electrode arranged to provide a visual glow display and an additional cathode electrode the glow from which is totally obscured by an opaque masking plate, the area of said additional cathode over which discharge takes place being substantially equal to the corresponding area of said display cathode or to the average of the corresponding areas of said display cathodes.

2. A gas discharge tube as claimed in claim 1 in which the anode electrode is in the form of a box surrounding the cathode electrodes, at least part thereof being formed from wire gauze or the like.

3. A cold cathode gas discharge tube comprising an anode electrode, a pair of cathode electrodes spaced and insulated from each other, said cathode electrodes having substantially the same size and shape, an optically opaque masking plate disposed between said cathode electrodes and having a light-transmitting aperture therein shaped and positioned to allow visual observation of only a portion of the glow discharge of one of said cathode electrodes whereby the cathode electrodes display different characters when the tube is viewed in the normal direction of observation.

4. A gas discharge tube as claimed in claim 3, said pair of cathode electrodes being cruciform, said aperture being in the form of a horizontal slot that exposes to view only the cross arm of one of the cathode electrodes where by the cathode electrodes display algebraic plus and minus signs.

References Cited UNITED STATES PATENTS 2,796,558 6/1957 Koehler 3l3--l09.5 3,244,923 4/1966 Milliken 313109.5 3,248,589 4/1966 Despris 313-1095 JAMES W. LAWRENCE, Primary Examiner.

R. L. JUDD, Assistant Examiner.