U.S. patent number 3,836,810 [Application Number 05/378,590] was granted by the patent office on 1974-09-17 for picture display device comprising a plurality of light producing elements.
This patent grant is currently assigned to U.S. Phillips Corporation. Invention is credited to Thijs Johannes De Boer, Edward Fokko De Haan, Johannes Hendricus Maria Johanns, Mathieu Martinus Maria Petrus Mattheij, Zeger Van Gelder.
United States Patent |
3,836,810 |
Johanns , et al. |
September 17, 1974 |
PICTURE DISPLAY DEVICE COMPRISING A PLURALITY OF LIGHT PRODUCING
ELEMENTS
Abstract
A gas-discharge picture-display panel comprising a plurality of
gas-discharge tubes. The gas-discharge tubes are closed on one side
by a window. An electrode is arranged at each end of each
gas-discharge tube. The length of the gas-discharge tubes is at
least twice the dimension normal to the directions of length and
the wall of the tube is coated with a phosphor material. A positive
column is formed in the gas-discharge tubes and the ultra-violet
radiation produced thereby causes the phosphor to luminesce. A
device which reduces the ignition voltage of the positive column is
connected in series with the gas-discharge tubes. The device
produces either a glow discharge or a plasma to reduce the ignition
voltage.
Inventors: |
Johanns; Johannes Hendricus
Maria (Emmasingel, Eindhoven, NL), De Boer; Thijs
Johannes (Emmasingel, Eindhoven, NL), De Haan; Edward
Fokko (Emmasingel, Eindhoven, NL), Van Gelder;
Zeger (Emmasingel, Eindhoven, NL), Mattheij; Mathieu
Martinus Maria Petrus (Emmasingel, Eindhoven, NL) |
Assignee: |
U.S. Phillips Corporation (New
York, NY)
|
Family
ID: |
26869196 |
Appl.
No.: |
05/378,590 |
Filed: |
July 12, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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173482 |
Aug 20, 1971 |
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Current U.S.
Class: |
313/484;
313/573 |
Current CPC
Class: |
H01J
61/42 (20130101); H01J 17/49 (20130101) |
Current International
Class: |
H01J
61/42 (20060101); H01J 61/38 (20060101); H01J
17/49 (20060101); H01j 061/42 () |
Field of
Search: |
;313/18R,18A,18B,185,188,196,220,225 ;315/169TV |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Demeo; Palmer C.
Attorney, Agent or Firm: Trifari; Frank R.
Parent Case Text
This is a continuation, application Ser. No. 173,482, filed Aug.
20, 1971, and now abandoned.
Claims
What is claimed is:
1. A picture display device comprising a first transparent,
insulating plate member having a first electrode system comprising
a plurality of elongated electrodes embedded in one surface
thereof, a second insulating plate member having a plurality of
longitudinal apertures orthogonal to its end surfaces and arranged
in rows and columns, one surface of said second member confronting
the surface of said first member having said electrodes embedded
therein, said longitudinal apertures corresponding with said
electrodes and having their walls coated with a phosphor material
capable of converting ultraviolet radiation into visible light, a
third insulating plate member having a plurality of additional
apertures communicating with said longitudinal apertures, a second
electrode system comprising a plurality of elongated electrodes
arranged between said second and third plate members and
corresponding with said apertures, and a third electrode system
arranged confronting the other surface of said third member, means
for sealing said first, second and third members to form a sealed
envelope, a mixture of mercury vapor and at least one rare gas for
filling said apertures at such a pressure as to form within said
sealed envelope a plurality of positive column discharges between
said first and second electrodes systems when ignited, the length
of said elongated apertures being at least twice the normal
dimension thereof, whereby an ionization voltage applied between
said second and third electrode systems reduces the ignition
voltage required for said positive column discharges.
2. A picture display device comprising a first transparent,
insulating plate member having a first electrode system comprising
a plurality of elongated electrodes embedded in one surface
thereof, a second insulating plate member having a plurality of
longitudinal apertures orthogonal to its end surfaces and arranged
in rows and columns, one surface of said second member confronting
the surface of said first member having said electrodes embedded
therein, said longitudinal apertures corresponding with said
electrodes and having their walls coated with a phosphor material
capable of converting ultraviolet radiation into visible light, a
second electrode system comprising a plurality of elongated
electrodes embedded in the other surface of said second member and
corresponding with said apertures, and a third electrode system
spaced apart from said second system, a sealing envelope enclosing
said electrode systems, a gas mixture filling said envelope at such
a pressure as to form positive column discharges within said
apertures when ignited whereby an ionization voltage applied
between said second and third electrode systems reduces the
ignition voltage required for said positive column discharges.
3. A device as claimed in claim 2, further comprising an additional
electrode means located in the space between the envelope and said
second electrode system.
4. A device as claimed in claim 3, wherein said additional
electrode means comprises a cathode and an auxiliary anode for
producing a plasma therebetween.
Description
The invention relates to a picture display device comprising a
plurality of gas-discharge tubes, each of which is closed at one
end by a window and is filled with a mixture of mercury and at
least one rare gas, the walls being coated with a luminescent
material, the length of each gas-discharge tube being at least
twice the dimension normal thereto, an electrode being provided on
either side of each gas-discharge tube. Such a picture display
device may be used for television and for the display of symbols,
for example, figures, letters, characters of electrical magnitudes
and the like. For this purpose the luminescent material of given
gas-discharge tubes of the device is caused to luminesce by
applying a voltage to said tubes. The device may be constructed so
that all electrodes located on one side of the discharge tubes are
separately taken to the outside so that the required voltage can be
applied separately to each discharge tube. In an alternative
construction the electrodes located on one side of the discharge
tubes are interconnected in a particular manner, which simplifies
the construction in the case of a large number of discharge tubes.
The electrodes located on either side of the discharge tubes may
then form separate grids of electrodes not intersecting each other,
while each electrode of one grid crosses all electrodes of the
other grid. In particular the electrodes of one grid cross those of
the other grid at right angles.
From U.S. Pat. No. 3,334,269 such a device is known, in which the
luminescent material on the wall of a discharge tube is caused to
luminesce by ultraviolet radiation, which is produced by a
discharge in a mixture of mercury and argon in the discharge tube
at the application of a voltage difference between the electrodes
of the discharge tube. From the description of said Patent
Specification it may be understood that the ultraviolet radiation
is produced by a glow discharge, since if in the device described
therein positive columns were produced, the latter could be
controlled at normal working temperature only with great difficulty
due to the high ignition voltage. At a higher temperature switching
would be facilitated, but the Patent Specification does not refer
anywhere to a high temperature during operation. Moreover in column
4 lines 45 to 49 only state as an advantage of the presence of the
luminescent material on the walls of the discharge tube that the
light produced is perceived without being reduced during its
passage through the phosphor layer, which does occur when the
phosphor is applied to the windows. This statement is not
indicative of the presence of a positive column. The Patent
Specification refers to the presence of a phosphor layer on the
window and to the presence of a phosphor layer on the tube wall as
being substantially equivalent alternatives. If the phosphor layer
is located on the window and if the ultraviolet radiation should
emanate from a positive column, only a very small portion of the
ultraviolet radiation would attain the phosphor layer on the window
due to the self-absorption of the ultraviolet radiation in the
positive column; this also is indicative of the absence of a
positive column. Since in a glow discharge a comparatively slight
ultraviolet radiation is produced, a small part of the energy
supplied is converted into visible light so that the efficiency of
the device is low, as shown by the low brightness.
The invention recognizer that an appreciably larger portion of the
energy supplied is converted into visible light, when a higher
amount of ultraviolet radiation is produced. This is achieved in
the case of a positive column of a suitable chosen gas discharge
i.e., of a mixture of mercury and at least one rare gas, the length
of the discharge tube being at least twice the dimension normal
thereto and the gas pressure being adapted to the diameter of the
discharge tubes in order to obtain a positive column. A difficulty
in obtaining a positive column resides in the comparatively high
ignition voltage required at normal working temperature. According
to the invention a positive column is formed in the gas discharge
tubes, while a device reducing the ignition voltage is connected in
series with the gas-discharge tubes. Said device comprises a
gas-discharge space freely communicating with the gas-discharge
tubes so that charge carriers can diffuse from said device to the
gas-discharge tubes. The phosphor material is applied to the walls
of the gas-discharge tubes. It is thus ensured that the
self-absorption of the ultraviolet radiation in the positive column
only has a minimum effect on the quantity of visible light
obtained. By means of the device reducing the ignition voltage of
the positive column in the gas-discharge tubes the picture display
device provides a high brightness, while its elements can be
separately switched on without the need for high voltages. For each
gas-discharge tube a separate device reducing the ignition voltage
may be provided, but as an alternative one
ignition-voltage-reducing device may be provided in common for a
plurality or all of the gas-discharge tubes.
In the case of a separate device reducing the ignition voltage of
the positive column for each gas-discharge tube a second
gas-discharge tube may be provided in series with each of said
gas-discharge tubes. The length of each of the second gas-discharge
tubes is at the most equal to the dimension normal thereto. On
either side of the second gas-discharge tube an electrode is
provided, while the first gas-discharge tube and the associated
second gas-discharge tube may have in common the intermediate
electrode. If the gas-discharge is ignited in the second
gas-discharge tube, which occurs at a comparatively low voltage
difference in view of the dimensions, a glow discharge is produced
owing to the dimensions. The presence of this glow discharge leads
to the production of a positive column in the associated first
gas-discharge tube at a comparatively low potential difference. The
operation may be as follows: the potential difference across a
given first gas-discharge tube is lower than the ignition voltage
required, if no further precautions were taken, but it is higher
than the ignition voltage required in the presence of a device
reducing the ignition voltage. When a glow discharge is produced in
the associated second gas-discharge tube, charge carriers therefrom
diffuse towards the first gas-discharge tube so that at this
potential difference a gas discharge is produced in the first
gas-discharge tube, which is a positive column owing to the
dimensions of the tube and to the gas pressure employed. The
switching operation is thus performed across the second
gas-discharge tube. A further mode of operation consists in that
the potential difference across a given first gas-discharge tube is
lower than the ignition voltage required in the presence of a
device reducing the ignition voltage. When a glow discharge is
produced in the associated second gas-discharge tube, charge
carriers diffuse towards the first gas-discharge tube. However, the
potential difference across the first gas-discharge tube is too low
for producing a discharge. When the potential difference across
this first gas-discharge tube is raised above the required ignition
voltage a gas discharge is ignited which is a positive column owing
to the tube dimensions and the prevailing gas pressure. The
switching operation then occurs via the first gas-discharge tube.
On the side remote from the window a second gas-discharge tube is
connected in series with each first gas-discharge tube, the length
of said second tube being at the most equal to the dimension normal
thereto, while on either side of each second-discharge tube an
electrode is provided. The first gas-discharge tube and the second
gas-discharge tube have, in particular, between them a common
electrode.
In further embodiment in which for each gas-discharge tube a
separate device is provided for reducing the ignition voltage of
the positive column said device may be arranged inside the
gas-discharge tube. For this purpose an additional electrode is
provided inside the gas-discharge tube at a short distance from the
electrode not located on the side of the window. The device
reducing the ignition voltage is then formed by the electrode not
located on the side of the window, the additional electrode and the
portion of the gas-discharge tube located between said two
electrodes. The distance between these two electrodes is at the
most equal to the dimension of the gas-discharge tube normal
thereto. If a gas-discharge is produced in said portion of the
gas-discharge tube, which occurs at a comparatively low potential
difference in view of the dimensions, a glow discharge is produced
in said portion of the gas-discharge tube owing to the dimensions.
The operation is similar to that described in the preceding
paragraph. In this case each gas-discharge tube comprises an
additional electrode located at a distance from the electrode not
located on the side of the window which is at the most equal to the
dimension of the gas-discharge tube at right angles to said
electrode.
In the two cases described the electrodes located on one side of
the second gas-discharge tubes or the additional electrodes may be
connected in a given manner so that, for example, they form a grid
of electrodes not intersecting each other. Various constructions
are possible, also in dependence upon the mode of switching. If a
second gas-discharge tube is provided and the first and the second
gas-discharge tubes a common electrode, the grids located on either
side of the second discharge tubes are formed each by electrodes
not intersecting each other, when switching is performed across the
second gas-discharge tubes, each electrode of one grid-crossing all
electrodes of the other grid, particularly, at right angles. The
grid located on the other side of the first gas-discharge tube is
formed by electrodes not intersecting each other. These electrodes
may be parallel to those of one of the grids located on either side
of the second gas-discharge tubes and are then normal to those of
the other one of said grids. This means that the first
gas-discharge tubes are located between two grids, the electrodes
of one grid crossing those of the other grid at right angles or the
electrodes of one grid being parallel to those of the other grid.
If a second gas-discharge tube is provided and a first and a second
gas-discharge tube have a common electrode, the grids located on
either side of the first gas-discharge tubes are formed by
electrodes not intersecting each other, when the switching
operation is performed across the first gas-discharge tubes, each
electrode of one grid crossing all electrodes of the other grid,
particularly, at right angles. The grid located on the other side
of the second gas-discharge tube is formed by electrodes not
intersecting each other and extending, for example, parallel to
those of one of the grids located on either side of the first
gas-discharge tubes. The same applies to the cases in which the
discharge tube in which a positive column is formed comprises an
additional electrode. In order to produce a gas-discharge
consecutively in two gas-discharge tubes, one of the electrodes of
which is associated with the same grid wire, each of the parallel
current paths required a separate resistance because owing to the
voltage drop across an active gas discharge it would not be
possible to ignite the second gas-discharge. This is usually
achieved by providing all electrodes of one grid with a resistor
outside the panel proper. A resistance may be provided in the panel
itself by providing all electrodes of one grid with a layer of
high-resistive material.
An embodiment in which a device reducing the ignition voltage is
common to a number or all of the gas-discharge tubes by providing
at least during a given period of the operation of the display
device a plasma for these gas-discharge tubes. The term "plasma" is
to denote a mixture of charged gas particles, which in total is
electrically about neutral. This plasma, common to the
gas-discharge tubes, is produced between a cathode and an auxiliary
anode. Various geometrical dispositions are possible, the cathode
and the auxiliary anode may be arranged so that the line of
connection between the cathode and the auxiliary anode is
approximately at right angles to the direction of the gas-discharge
tubes. In another geometrical arrangement the auxiliary anode is
located between the cathode and the gas-discharge tubes. In this
case the auxiliary anode need not be common to all those
gas-discharge tubes, to which the cathode is common. The phosphor
of a given gas-discharge tube is excited when the potential
difference across said gas-discharge tube exceeds the burning
voltage, whereas it is nevertheless lower than the ignition voltage
which would be required if no further precautions were taken. Since
charge carriers diffuse from the plasma into the gas-discharge
tube, sufficient pre-ionisation is obtained in the gas-discharge
tube for starting the discharge. The gas-discharge tubes whose
phosphors should not be excited have a potential difference which
is lower than the burning voltage. In this case the switching-on
operation is performed by controlling the potential difference
across the gas-discharge tube. The device reducing the ignition
voltage is thus formed by a cathode and an auxiliary anode, between
which a plasma common to at least a number of the gas-discharge
tubes is produced. In dependence upon the voltage applied the
positive column is formed between the electrodes on either side of
the gas-discharge tube or between the cathode of the plasma and the
electrode located on the other side of the gas-discharge tube. If
the electrodes on either side of the gas-discharge tubes are
interconnected and thus form grids of electrodes not intersecting
each other, each electrode of one grid crosses all electrodes of
the other grid, particularly, at right angles. It is furthermore
possible to arrange in line with each first gas-discharge tube a
second gas-discharge tube between the former and the plasma, an
electrode being provided on either side of said second tube, the
intermediate electrode being common to the first and the associated
second gas-discharge tubes. The overall potential difference across
the first and the associated second gas-discharge tubes is then
always higher than the burning voltage. The switching operation is
not performed by varying this overall potential difference, but it
results from a variation of the voltage at the intermediate
electrode, that is to say, a variation of that portion of the
potential difference which occurs across the second gas-discharge
tube. This second gas-discharge tube then operates like a valve.
The plasma is capable of reducing the ignition voltage for those
first gas-discharge tubes for which the potential difference across
the associated second gas-discharge tubes is so high that charge
carriers can penetrate into the first discharge tubes. This has the
advantage that the main current need not be switched. Between the
gas-discharge tubes and the device reducing the ignition voltage it
is preferred in this case to connect a second gas-discharge tube in
series with every first gas-discharge tube, an electrode being
provided on either side of each second gas-discharge tube.
It should be noted that U.S. Patent No. 2,595,617 discloses a
picture display device comprising a plurality of gas-discharge
tubes whose windows are coated with a phosphor, there being
provided a common compartment in which a spare quantity of ionized
gas or vapour is produced, which constitutes a kind of plasma.
Though in this Patent Specification the terms "column" and
"positive column" are used, it is obvious from many paragraphs of
the specification that the phosphor material is caused to luminesce
by electron excitation. It is stated, for example, in column 12,
lines 70 to 72, that electric charges in each cell locally act upon
the fluorecent layer. Moreover, a modulation of the resultant
brightness by the control of the anode voltage as stated in column
4, lines 39 to 41, is only possible in the case of electron
excitation. In addition, at the low pressure referred to the gases
(mercury vapour, hydrogen and helium) mentioned in column 3, lines
67 to 68 provide only a very slight ultraviolet radiation. The
phosphor material is applied to the window; if ultraviolet
radiation were produced, only a very small portion of the
ultraviolet radiation would attain the phosphor material on the
window due to the self-absorption of the ultraviolet radiation in
the positive column.
In the device embodying the invention the phosphor material
arranged on the walls of the gas-discharge tubes determines the
colour of the emitted light. By using materials luminescing in
different colours a device is obtained for displaying colour
pictures.
The brightness obtained is further increased by providing
light-reflecting properties for the wall of the gas-discharge tube
coated with the phosphor material.
The invention will be described by way of example with reference to
a drawing which shows
in FIG. 1 a cross sectional view of part of a display panel,
in FIG. 2 part of a developed view of the diaplay panel of FIG.
1,
in FIG. 3 a sectional view of a different construction of the
display panel,
in FIG. 4 a sectional view of a further structure of a display
panel and
in FIG. 5 also a sectional view of a further structure of a display
panel.
FIG. 1 is a cross sectional view of part of a display panel
embodying the invention. It comprises a glass plate 1, a first grid
of parallel wires, a wire 2 being shown in the Figures, a glass
plate 3 having apertures 4, 5, 6, 7, 8, 9 and 10, a second grating
of parallel wires 11, 12, 13, 14, 15, 16, 17, a glass plate 18
having apertures 19, 20, 21, 22, 23, 24, and 25 registering with
the apertures in the plate 3, a third grating of parallel wires, a
wire 26 being shown in the Figures, and a metal cover 27, which is
connected by an insulating intermediate piece 28 with the plate 18.
The wires of the first grating are sunk in grooves in the plate 1
and the wires of the second grating and those of the third grating
are sunk in grooves of the plate 18. The walls of the aperture of
the plate 3 are coated with a layer 29 of a phosphor. The apertures
in the plates 3 and 18 are filled with a mixture of mercury and at
least one rare gas. The sealed exhaust and filling opening is not
shown in the Figure.
FIG. 2 is part of a developed view of the display panel of FIG. 1.
The glass plate 1 has vertical grooves 30, 31, 32, 33 and 34,
accommodating wires 35, 36, 37, 38 and 39 of the first grating. One
of these wires corresponds with the wire 2 of FIG. 1. The glass
plate 3 has apertures in an array of vertical columns and
horizontal rows, a number of which is shown, i.e., 40, 41, 42, 43,
44, 45, 46, 47, 48, 49 and 50. The apertures of one of the columns
correspond with the apertures 4, 5, 6, 7, 8, 9 and 10 of FIG. 1.
The glass plate 18 is provided on one side with horizontal grooves
51, 52, 53, 54 and 55, accommodating wires 56, 57, 58, 59 and 60 of
the second grating. These grooves correspond with a number of
grooves of FIG. 1, which also applies to said wires and a number of
the wires 11, 12, 12, 13, 14, 15, 16 and 17 of FIG. 1. On the other
side the glass plate 18 has vertical grooves 61, 62, 63 holding
wires 64, 65 and 66 of the third grating one of these wires
corresponds with the wire 26 of FIG. 1. At the crossings of the
grooves 51, 52, 53, 54 and 55 with the grooves 61, 62, 63 the plate
18 has apertures 67, 68, 69, 70, 71, 72, 73, 74, 75, 76 and 77. The
apertures in one of the columns correspond with a number of the
apertures 19, 20, 21, 22, 23, 24 and 25 of FIG. 1. FIG. 2
furthermore shows the metal cover 27 and the insulating
intermediate piece 28.
In a practical embodiment the apertures in the plates 3 and 18 have
a diameter of 1 mm. The length of the apertures in the plate 3 is 5
mms and that of the apertures of the plate 18 is 0.5 mm. The
apertures are filled with a mixture of saturated mercury vapour and
argon at a pressure of 7 cms Hg. The wires of the first, second and
third gratings have a thickness of 0.1 mm and are held in grooves
of a depth of 0.1 mm and a width of 0.1 mm. The apertures in the
plate 3 are coated with a reflective layer of titanium oxide, on
which a phosphor layer of calcium halophosphate is provided. This
material produces white light. In the operation of this display
panel the wires of the first grating and the wires of the second
grating have a potential difference of 350 V. This potential
difference is not sufficient to ignite a positive column in the
apertures of the plate 3. If a potential difference of 300 V
prevails between a given wire of the second grating and a given
wire of the third grating a glow discharge is produced in the
aperture concerned in the plate 18 owing to the geometry of the
aperture therein. Charge carriers then diffuse towards the
corresponding aperture in the plate 3 and provide a reduction of
the ignition voltage so that at said potential difference of 350 V
a positive column is ignited in the aperture concerned of the plate
3. The ultraviolet radiation produced therein causes the phosphor
in said aperture to luminesce. The switching operation is performed
in this case by controlling the potential difference between the
wire of the second grating and those of the third grating.
FIG. 3 is a sectional view of another construction of the display
panel. It comprises a glass plate 101, a first grating of vertical
wires, a wire 102 being shown in the Figure, a glass plate 103
having apertures 104, 105, 106, 107, 108, 109 and 110, the walls of
which are coated with a layer 111 of a phosphor, a second grating
of horizontal wires 112, 113, 114, 115, 116, 117, and 118, a glass
ring 119, through which a supply wire 120 for an auxiliary anode
121 and a supply wire 122 for an auxiliary cathode 123 are taken,
and furthermore a metal cover 124. The wires of the first and
second gratings are held in grooves in the plate 103. The panel is
filled up with a mixture of mercury and at least one rare gas. The
ignition voltage of the positive column to be produced in one or
more of the apertures in the plate 103 is reduced in this case by
the plasma formed at a given potential difference between the
auxiliary cathode 123 and the auxiliary anode 121. The switching
operation is performed by varying the potential difference between
the wires of the first grating and those of the second grating.
FIG. 4 is a sectional view of a further structure. Apart from the
device reducing the ignition voltage the parts are identical to
those of FIG. 3 and designated by the same reference numerals. The
panel comprises a glass ring 125, through which a supply wire 126
for an auxiliary anode 127 and supply wires 128 for an auxiliary
cathode 129 are passed and furthermore a metal cover 130. The
ignition voltage of the positive column to be produced in one or
more of the apertures of the plate 103 is reduced by the plasma
formed at a given potential difference between the auxiliary
cathode 129 and the auxiliary anode 127.
FIG. 5 is a sectional view of a further variant of the structure of
a display panel. It comprises a glass plate 131, a first grating of
vertical wires, the wire 132 being shown in the Figure, a glass
plate 133 having apertures 134, 135, 136, 137, 138, 139 and 140,
the walls of which are coated with a layer 141 of a phosphor, a
second grating of vertical wires, the wire 142 being shown in the
Figure, a glass plate 143 having apertures 144, 145, 146, 147, 148,
149 and 150, registering with the apertures of the plate 133, a
third grating of horizontal wires 151, 152, 153, 154, 155, 156, 157
a glass ring 158, through which a supply wire 159 for an auxiliary
anode 160 and supply wires 161 for an auxiliary cathode 162 are
taken, and furthermore a metal cover 163. The wires of the first
grating are held in grooves of the plate 133 and the wires of the
second and third gratings are held in grooves of the plate 143. The
panel is filled up with a mixture of mercury and at least one rare
gas. The ignition voltage of the positive column to be produced in
one or more of the apertures in the plate 133 is reduced in this
case by the plasma produced at a given potential difference between
the auxiliary cathode 162 and the auxiliary anode 160. The ignition
voltage of the positive column is only reduced at those apertures
in the plate 133 at which the potential difference from the
associated apertures in the plate 143 is so high that charge
carriers of the plasma can diffuse through the aperture in the
plate 143 into the aperture of the plate 133. The switching
operation is performed in this case by varying the potential
difference between the wires of the second grating and those of the
third grating. The gas-discharge tubes in the plate 133 operates as
a kind of valve.
* * * * *