GB2201036A - Visual display panel - Google Patents

Abstract

A visual display panel suitable for use at high altitude comprises two confronting glass plates 1, 2 sealed at their periphery, the plates carrying electrically conductive tracks such that a luminous electric discharge can be formed between said plates, the discharge taking place through a low pressure gaseous atmosphere confined therebetween, in which the panel is supported in a sealed enclosure formed by plates 7, 8 which contains a gaseous atmosphere at a pressure higher than that between the said plates. A mesh screen prevents electromagnetic interference. <IMAGE>

Description

VISUAL DISPLAY PANEL This invention relates to a visual display panel.

It relates particularly to the kind of display panel which makes use of a luminous plasma discharge which is established through a gaseous atmosphere such as neon. Plasma panel displays usually comprise two glass plates sealed at their periphery, the chamber so formed being filled with a neon gas at a pressure of about 0.5 atmosphere (7.5 psia). Electrically conductive tracks are formed in the facing surfaces of the glass plates.

By applying electrical potentials to the conductive tracks a luminous electric discharge forming a pixel is created where tracks on the opposing glass plates intersect. The gap between the opposing glass track surfaces is made rather small, of the order of 0.1 millimetre, and the accurate maintenance of this gap length is thus critical to the satisfactory performance of the plasma panel.

At ground level, the glass plates will tend to be pressed together by the differential gas pressures and the minimum gap length can be fixed by glass distance pieces so that the correct gap will be set. At a high altitude, the ambient air pressure will fall below the neon gas pressure at about 20,000 feet, and from this point upwards the gap length will then progressively increase.

Eventually, the increase in the gap length will cause the plasma arc to break and at still greater heights the ambient pressure could be so low that the glass plates would tend to become overstressed and thus may be destroyed.

The present invention was devised to provide a display panel which would have a reduced sensitivity to external pressure variations.

According to the invention, there is provided a visual display panel comprising two confronting glass plates sealed at their periphery, the plates carrying electrically conductive tracks such that a luminous electric discharge can be formed between said plates the discharge taking place through a low pressure gaseous atmosphere confined therebetween; in which the panel is supported in a sealed enclosure which contains a gaseous atmosphere at a pressure higher than that between the said plates. Conveniently, the sealed enclosure may comprise one or more glass plates which are arranged parallel to the plates of the display panel.

Preferably, each glass plate of the display panel also constitutes a wall of a sealed enclosure in which a gas pressure higher than that between the said plates is provided. The display panel may thus have a separate sealed enclosure located on both the front and the rear walls of the panel. At least one of the walls on the rear side of the panel may be non-transparent. The non-transparent wall of the panel or the enclosure may be made of a metal.

On a front wall of the panel or the enclosure, a screen against electromagnetic interference (EMI) may be located. Such a screen serves to prevent EMI from entering the display panel as well as preventing EMI from the display panel affecting other equipment.

The screen may comprise a wire mesh sheet which is laminated within a glass plate of the front wall.

By way of example, a particular embodiment of the invention will now be described with reference to the accompanying drawing in which: Figure 1 is a perspective view of a standard plasma visual display panel, Figure 2 is a cross-sectional view of the panel of Figure 1, Figure 3 is a cross-sectional view of a panel according to the present invention.

Figure 4 is a graph showing the number of pixel faults which can occur in a display panel with increasing altitude, and, Figure 5 shows the failure pattern which can occur in a display panel at high altitude.

As depicted in Figure 1, a standard plasma display panel comprises a front glass plate 1 and a rear glass plate 2. Electrically conductive tracks 3 ate provided on the confronting surfaces of each glass plate.

Figure 2 shows that the plates 1 and 2 are sealed together by a bond 4 at the plate periphery in a manner which leaves a narrow gap 6 formed between the confronting plate surfaces.

In operation of the display panel, the gap 6 which has a gap length of about 0.1 millimetre is filled with a neon gas at a pressure of about 0.5 atmosphere (7.5 psia). The bond 4 ensures that this gaseous atmosphere is permanently sealed between the plates.

When a suitable electrical potential is applied to one of the tracks 3 on the front glass plate 1 and a potential of opposite polari to a track on the rear glass plate 2, a capacitive discharge will take place at the point on the panel where the two tracks intersect. This discharge will occur through the neon gas atmosphere between the plates and it will be visible as a luminous spot to an observer looking towards the front glass plate of the display panel.

Whilst this arrangement works satisfactorily at ground level, if the display panel is required for use in an aircraft there is a possibility that the surrounding atmosphere will be at a much reduced pressure level, the plates 1 and 2 would bow outwards and consequently the gap 6 could lengthen. The result of this would be that the required discharge would fail to strike at the available voltage.

Figure 3 shows the construction of the invention where the front glass plate 1 is provided with an external enclosure constituted by a glass sheet 7 sealed to the plate 1 by a bond 4.

Similarly, the rear glass plate 2 is provided with an external enclosure constituted by a glass sheet 8 sealed to the plate 2 by a bond 4.

The two sealed enclosures are filled with a gaseous atmosphere at a pressure above that in the gap 6. A preferred level of gas pressure for these enclosures is one atmosphere. Since the enclosure pressures always exceed the plasma gas pressure, the gap for discharge of the plasma will remain unchanged under low pressure conditions and there will be no additional mechanical stress likely to be placed on the glass plates 1 and 2.

As depicted in Figure 3, the glass -sheet 7 forming the front wall of the enclosure is provided of a laminated toughened glass construction and this incorporates a wire mesh screen 9. The mesh screen 9 is bonded to an outer casing of the display device and earthed. It acts to provide protection to the display panel against the effects of electromagnetic interference as well as preventing interference from the display. The screen also acts to limit any damage that may occur in the event of a fracture of the glass sheet.

Since there is only a tiny gas volume sealed between the glass surfaces this minimises the likelihood of doing damage if the pressurized container which this construction represents should become accidentally broken at a high altitude.

Figure 4 is a graph which illustrates the display panel behaviour at different altitudes. The graph shows on the vertical axis altitude above sea level in units of thousands of feet and on the horizontal axis the number of pixel display faults that were observed in operation of the panel over a fixed time period.

The curves show the effects with typical known constructions of plasma display panels having a six millimetre thick glass front plate (Curve A) and with a thirteen millimetre front plate (Curve B).

It will be seen that with the lower thickness of glass plate the operation is satisfactory at altitudes up to about 20,000 feet but above this level the displayed pattern deteriorated rather sharply due to the outward bowing of the glass panels.

The use of the greater thickness of glass (Curve B) delays the onset of pixel failure to about 35,000 feet but deterioration occurs again as the altitude approaches 40,000 feet.

The Curve C which approximates to a vertical straight line illustrates the behaviour of the display panel of the present invention. The embodiment tested was constructed using a six millimetre thick sheet for the front plate 1 and this was then covered with a glass sheet 7 comprising two five millimetre thick glass panels enclosing a wire mesh screen 9. The construction of the invention therefore was found not to exhibit any indication of pixel failure up to an altitude of 60,000 feet.

Figure 6 illustrates the effect on the operation of the aforementioned known construction of display panel as different altitudes are attained. In this example, the construction embodies a six millimetre thick glass plate and this has a display area 11 measuring nine inches square.

At an altitude of 23,000 feet, the outward bowing of the glass panel causes a relatively small portion (P) of the area being displayed to disappear. A-gradual degradation of the area of pixels at the centre of the screen has thus taken place. At 30,000 feet, a substantial portion (Q) of the central display area has gone and at 50,000 feet the whole of the central portion (R) is missing.

These effects do not occur in the display panel of the invention because the presence of the external enclosure in front of the front glass plate 1 acts to prevent the boaring of the plate 1 under low pressure conditions. When the ambient air pressure changes from 15 psia to, say, I psia at 60,000 feet this is likely to have only a minor effect on the front wall 7 of the enclosure within which a pressure of one atmosphere has been provided. There will be no measurable effect on the front glass plate 1 which could effect the operation of the visual display. A similar enclosure acts to stabilise the rear glass plate 2 of the display device.

The visual display panel of the invention has been found particularly suitable for use in an aircraft environment at high altitudes since the accidental depressurisation of the aircraft cabin atmosphere is unlikely to cause a simultaneous operational failure of the display device. The display panel is able to be constructed of a reduced thickness of glass as compared with some of the conventional display device constructions and yet is able to maintain an effective display operation at altitudes very much greater than those at which the conventional displays cease their operation. The display panel of the invention is thus able to be made lighter in weight - than some of the conventional display devices.

The foregoing description of an embodiment of the invention has been given by way of example only and a number of modifications may be made without departing from the scope of the invention as defined in the appended claims.

For instance, the material for the rear plate 2 or the rear sheet 8 of the panel construction instead of glass may be of some other suitable material such as a metal.

Claims (6)

1. A visual display panel comprising two confronting glass plates sealed at their periphery, the plates carrying electrically conductive tracks such that a luminous electric discharge can be formed between said plates the discharge taking place through a low pressure gaseous atmosphere confined therebetween, in which the panel is supported in a sealed enclosure which contains a gaseous atmosphere at a pressure higher than that between the said plates.

2. A visual display panel as claimed in Claim 1, in which the sealed enclosure comprises one or more glass plates which are arranged parallel to the plates of the display panel.

3. A visual display panel as claimed in Claim 1 or 2, in which one of the glass plates of the panel also acts as a wall of said sealed enclosure.

4. A visual display panel as claimed in any one of Claims 1 to 3, in which said panel carries a sealed enclosure located on both of the front and rear walls of the panel.

5. A visual display panel as claimed in any one of Claims 1 to 4, in which one of said glass plates includes a wire mesh sheet arranged to provide electromagnetic screening.

6. A visual display panel substantially as hereinbefore described with reference to Figure 3 of the accompanying drawing.