The service of such as system is quite easy. It consists of cleaning the system so that it is free from dust, and making readjustments to the system itself. It is normally sufficient to service the equipment one to two times per year. In case of a lamp failure, the systems supplied by most vendors have automatic double-lamp systems. In the event of a lamp failure, the system switches automatically to a second (backup) lamp. It should be possible to change the broken lamp during working operations. This task is quite easy and trained operators should be able to do this by themselves.
GLOSSARY
Aspect Ratio: The ratio of the display width to the display height. The aspect ratio of a traditional television is 4:3, but there is an increasing trend towards the 16:9 ratio typically used by consumer large screen, high-definition televisions.
Brightness: The amount of light emitted from a display. It is sometimes synonymous with the term ‘luminance’, which is defined as the amount of light emitted in a given area and is measured in candela per square metre.
Burn-In: Phosphor, the illuminant in CRT and plasma screens, subject to a natural ageing process. If images are unchanging for a long time, this can lead to the image ‘burning in’.
CCTV: Closed-circuit television, a television system often used for surveillance.
Contrast Ratio: Defined as the ratio of the luminance of the brightest colour to the luminance of the darkest colour on the display. High-contrast ratios are demanded but the method of measurement varies greatly. They can be measured with the display isolated from its environment or with the lighting of the room being accounted for. Static contrast ratio is measured on a static image at some instant in time. Dynamic contrast ratio is measured on the image over a period of time. Manufacturers can market either static or dynamic contrast ratio depending on which one is higher.
DCS: Distributed control system. In DCS, the controller itself controls the process. It has the control loops in the controller. It communicates through the high-speed Ethernet/LAN network. DCS is confined to a single unit or group of local units. Examples of uses: control system of all process plants, including refinery (petroleum), chemical plants, power plants, etc.
DLP: Digital light processing technology; with digital micromirror device (DMD), from Texas Instruments.
Graphics Controller, Display Processor, Display or Split Controller: A type of controller that splits up a video or computer signal into multiple part images so that they can be displayed on multiple screens (4, 9, 16, 25, …) to create the full image again. In general, inside these controllers you have the possibility to add several different input cards to show these sources on the large screen; these inputs can be: analogue video, IP or streaming video, RGB, DVI, or SDI signals. For example, it is possible to have an integrated split controller in displays for a 2 x2 or 3 x 3 video walls.
Memory Effect, Image Retention, Ghost-Images: Images that remain on the screen. One of the advantages of LCD displays compared to plasma is that LCD does not have the problem of permanent burn-in when displaying a static picture for a long time (for example, a company logo that is always present at a particular corner on the screen). But LCD displays also suffer from a similar type of image retention. The image retention that may appear on LCD displays is called memory effect or ghost-images; it is not permanent and can be reversed. Also LCD displays are not so sensitive to this effect; like on plasma, this can occur just after a few hours of use. It occurs on LCD displays when ionic contaminants in the panel migrate to the surface (usually caused by electromagnetic interference) and accumulate to areas in the panel where a static image is displayed. This will cause a drop in the drive voltage in that area and the static image remains visible even after the particular image is changed. Once the image is changed, the impurities will, with time, migrate out of the area and the memory effect should disappear. The time it takes for the image retention to disappear depends on how severe it was in the first place, and in some cases it takes so much time and effort that for all practical purposes it could be called permanent. Switching off the LCD for 4 to 6 hours during 24-hour operations could also be a solution. Also very important to prevent this image retention is the cooling of the display.
Mimic or Mosaic Display: Panels, consisting of several small LED lights, used for illuminated mimic diagram; indication and control panels; distribution of gas, oil, steam and other liquids; different industrial process with status indication; control and signalling systems of railways.
Pixel: Picture element, using the abbreviation ‘pix’ for ‘picture’; a single point in a graphic image. Each such information element is not really a dot or a square, but an abstract sample. With care, pixels in an image can be reproduced at any size without the appearance of visible dots or squares; but in many contexts, they are reproduced as dots or squares and can be visibly distinct when not fine enough. The intensity of each pixel is variable; in colour systems, each pixel has typically three or four dimensions of variability such as red, green, and blue, or cyan, magenta, yellow, and black. Standard display resolutions include:
• VGA 0.3 Megapixels = 640 x 480
• SVGA 0.5 Megapixels = 800 x 600
• XGA 0.8 Megapixels = 1024 x 768
• SXGA 1.3 Megapixels = 1280 x 1024
• SXGA+ 1.4 Megapixels = 1400 x 1050
• UXGA 1.9 Megapixels = 1600 x 1200
• HDTV 2.1 Megapixels = 1920 x 1080
• QXGA = 2048 x 1512
• QSXGA = 2560 x 2048
• Quad HDTV 8.3 Megapixels = 3840 x 2160
Plasma Display: Plasma display panel (PDP), a type of flat-panel display nowadays commonly used for large TV displays (typically above 37” or 940 mm). Many tiny cells located between two panels of glass hold an inert mixture of noble gases (neon and xenon). The gas in the cells is electrically turned into a plasma which then excites phosphors to emit light. Plasma is, in general, used in the home environment.
Resolution: The number of pixels in each dimension on a display. In general, a higher resolution will yield a clearer, sharper image. It is normally expressed in pixels.
Response Time: The time it takes for the display to respond to a given input. For an LCD display, it is defined as the total time it takes for a pixel to transition from black to white, and then back to black. A display with slow response times displaying moving pictures may result in blurring and distortion. Displays with fast response times can make better transitions in displaying moving objects without unwanted image artefacts.
SCADA (Supervisory Control and Data Acquisition): Systems that are typically used to perform data collection and control at the supervisory level. Some SCADA systems only monitor without doing control; these systems are still referred to as SCADA systems. The supervisory control system is a system that is placed on top of a real-time control system to control a process that is external to the SCADA system. In SCADA systems, the operator/super – visor collects alarm/event data from the remote terminal unit (RTU) or programmable logic controllers (PLCs) along the service line. The operator analyses the data (alarms and SOEs [sequence of events]) and takes action if required. The RTU/PLC is the local control system that works as per the command received from the supervisory system, except for some specific control decisions (fire fighting, emergency shutdown) taken locally by the RTU/PLC. The communication path is wireless, GSM tech. (Global System for Mobile Communications), etc. Examples of uses for control are: water supply pipelines, gas/petroleum pipelines, and so forth.
TFT-LCD (Thin Film Transistor-Liquid Crystal Display): A variant of liquid crystal display (LCD) which uses thin film transistor (TFT) technology to get better image quality. TFT-LCD is one type of active matrix LCD, though it is usually synonymous with LCD. It is used in televisions, flat- panel displays, and projectors.
Viewing Angle: The maximum angle at which the display can be viewed with acceptable quality. The angle is measured from one direction to the opposite direction of the display, such that the maximum viewing angle is 180°. Outside this angle the viewer will see a distorted version of the image being displayed. Definitions of what is acceptable quality for the image can be different among manufacturers and display types. Many manufacturers define this as the point at which the luminance is half of the maximum luminance. Some manufacturers define it based on contrast ratio and look at the angle at which a certain contrast ratio is realised.
REFERENCES AND FURTHER READING
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IBM. (1979). Human Factors of Workstations with Display Terminals, G 320-6102. New York: International Business Machines.
Schaller, Robert R. (1997). Moore’s Law: Past, Present and Future. IEEE Spectrum 34, 6, 52-59.
Songer, A. D., and North, C. (2004). Multidimensional Visualization of Project Control Data. Construction Innovation 4, 173-90.
Stark, L., and Ellis, S. (1981). Cognitive Models Direct Active Looking. In Dennis F. Fisher, Richard A. Monty, and John W. Senders (eds.), Eye Movements: Cognition and Visual Perception. Hillsdale, NJ: Erlbaum Press.
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Stone, P. T., and Groves, S. (1968). Discomfort Glare and Visual Performance. Transactions of the Illumination Engineering Society 1, 10-19.
Van Laar, Darren, and Deshe, Ofer. (2007). Color Coding of Control Room Displays: The Psychocartography of Visual Layering Effects. Human Factors 49, 3, 477-90.
