What is CRT?
A cathode ray tube (CRT) is a type of analog display device. Cathode ray tubes are special, electronic vacuum tubes that use focused electron beams to display images.
What is the common use for CRT?
Most famous for their use in such things as televisions, oscilloscopes, computer and radar displays, and automated teller machines. Cathode ray tubes are also used in video game equipment.
How does a CRT monitor work?
Inside a CRT monitor is a picture tube that narrows at the rear into a bottleneck. In the bottleneck is a negative charged filament or cathode enclosed in a vacuum. When electricity is supplied, the filament heats up and a stream or "ray" of electrons pours off the element into the vacuum. The negatively charged electrons are attracted to positively charged anodes which focus the particles into three narrow beams, accelerating them to strike the phosphor-coated screen. Phosphor will glow when exposed to any kind of radiation, absorbing ultraviolet light and emitting visible light of fluorescent color. Phosphors that emit red, green and blue light are used in a color monitor, arranged as "stripes" made up of dots of color. The three beams are used to excite the three colors in combinations needed to create the various hues that form the picture.
To precisely direct the beams, copper steering coils are used to create magnetic fields inside the tube. The fields move the electron beams vertically or horizontally. By applying varying voltages to the steering coils, a beam can be positioned at any point on the screen. Each image is painted on the screen -— and repainted -- several times each second by scanning the electron beams across the screen at incredible rates. This must be done even when the picture being displayed is unchanging, because the phosphor only glows for a very short time.
Who are the leading providers for the said device?
• Samsung
• LG
• Acer
• Asus
How does it differ from other similar devices?
Direct-view CRT HDTV Displays
Pros CRT:
• Flat screen – which provides wide viewing angles (most new CRT’s built today have flat screens, but you will still find a few that have are manufactured with curved screens)
• Outstanding picture quality
• Relatively inexpensive in all sizes
• No danger of burn-in
• Capable of producing true blacks
Cons – CRT vs. other display technology
• Bulky size and very heavy weight
• Maximum screen size is limited to approximately 36"
To give you an idea of what is meant by “bulky" and “very heavy", a typical 27" flat screen CRT will weigh around 100-120 lbs, a typical 30" flat screen CRT will weigh about 150 lbs and a typical 36" flat screen CRT will tip the scales at about 200-225 lbs. At over 200 lbs., that kind of weight is going to require at least 2 strong people to lift it up onto the TV stand.
Why should I choose a flat screen CRT over a curved screen CRT?
1) Having a flat-screen will allow for wider viewing angles, so that you can those people sitting on the left and right sides of the TV also have a good view of the images being displayed.
2) Having a flat screen will allow you to view the picture as it was meant to be seen, without any of the stretching in images that is associated with a curved tube. A curved tube has inherent flaws that cause the image to be “stretched" as it reaches the edges of the screen. While this may not be an important feature for you, I would encourage you to look at a flat screen and a curved screen side-by-side. The difference in image quality will be much more apparent.
Flat panel LCD HDTV Displays
The main advantages of LCD’s include:
• Thin, lightweight and stylish looking
• High resolution and excellent picture quality
• No danger of burn-in
• Flat screen – but see below for note on the viewing angles
Flat panel LCD’s main disadvantages:
• Relatively narrow viewing angles
• Expensive in sizes over 30"
• Incapable of producing true blacks
To give you an idea of what “thin" and “lightweight" means, a typical 27" to 30" LCD will weigh about 40-50 lbs, a 32" LCD will weigh about 50-55 lbs, a 37" LCD will weigh about 60-65 lbs. These types of TV’s are thin and light enough to be hung on a wall.
Plasma HDTV Displays
Plasma TV
Advantages of plasma TV’s:
• Flat screen with very wide viewing angles
• Very thin and lightweight
• High resolution with deep, saturated colors
• Excellent picture quality (especially for home theater)
Plasma’s main disadvantages:
• Fairly expensive compared to other HDTV display types
• Slight potential for burn-in
• Limited lifespan
To clarify “thin" and “lightweight", a typical 42" plasma will weigh between 50-90 lbs, 50" plasma will weigh about 80-110 lbs. These types of TV’s are thin and light enough to be hung on a wall.
Are there other possible uses for the device aside from what it is designed for?
Storage CRTs
Other graphical displays used 'storage tubes', including Direct View Bistable Storage Tubes (DVBSTs). These CRTs inherently stored the image, and did not require periodic refreshing. Some were quite large, on the order of 20 inch diagonals. Oscilloscopes also used storage tubes, in particular for observing (and, if needed, photographing) single events or very-slowly-changing signals. Some storage tubes have a special plate behind the phosphor display screen. The imaging electron gun writes its trace onto the plate, and where written, the plate permits electrons from another electron gun to pass through it onto the display screen. The latter gun, called a flood gun, covers the whole area of the plate evenly with electrons; it is not at all a focused beam.
Some storage tubes could display continuous-tone images.
Another type of storage tube, used in oscilloscopes and large-screen direct-view X-Y displays, has a special phosphor screen structure that normally blocks electrons from exciting the phosphor, but when written onto, lets the flood-gun's electrons maintain the written trace.
A typical storage CRT's image starts to deteriorate after tens of seconds to minutes; it is by no means permanent.
Charactrons
Some displays for early computers (those that need to display more text than practical using vectors, or that require high speed for photographic output) use Charactron CRTs. These incorporate a perforated metal character mask, which shapes a wide electron beam to form a character on the screen. The system selects a character on the mask using one set of deflection circuits, but that causes the extruded beam to be aimed off-axis, so a second set of deflection plates has to re-aim the beam so it is headed toward the center of the screen. A third set of plates places the character wherever required. The beam is turned on briefly to draw the character at that position. Graphics could be drawn by selecting the position on the mask corresponding to the code for a space (in practice, they were simply not drawn), which had a small round hole in the center; this effectively disabled the character mask, and the system reverted to regular vector behavior. Charactrons had exceptionally-long necks, because of the need for three deflection system
Monoscopes
A monoscope is a special form of cathode ray tube that is used to generate, rather than display, a video signal. Each tube is only capable of generating a single video signal, hence the name.
Dark-trace tubes
These tubes, instead of a light-emitting phosphor, had a faceplate coated with a scotophor, composed of potassium chloride (KCl), and designated P10. Electron impact made the KCl absorb green light, giving a magenta-colored trace. Trace persistence was quite long, but could be shortened by infrared heating of the faceplate. They were used in World War II large-screen radar displays.
Camera tubes
Camera tubes were the image sensors in TV cameras until the 1980's. One of the earliest was the iconoscope, invented and developed by Vladimir Zworykin at RCA. Another early one was the image dissector, invented by Philo T. Farnsworth, and used even recently for monitoring flames in commercial boilers. Philo Farnsworth created the first all-electronic television system.
A tube called the orthicon was refined into the image orthicon, which was the professional camera tube of choice for several decades. Image orthicons were sophisticated, not easy to make, but their image quality was very good.
A much-simpler, much smaller and much less-costly camera tube called the vidicon was popular for small closed-circuit TV cameras, such as security cameras. It spawned many variations, distinguished principally by the material used for its photosensitive surface.
Scan converters
These are uncommon, and used to convert, for example, from radar PPI display video to a raster scan. They are effectively two CRTs facing a common screen. One is a display-type tube that write data onto the screen, which stores it for a while (long persistence), and the other is like a camera tube.
The PPI (Plan Position Indicator) is familiar in some TV weathercasts as a decorative animated graphic element—a rotating radial bar of light on a circular screen.
Date Visisted: August 4, 2009
Sources:
www.hackaday.com/2008/02/25/hackit-new-uses-for-old-crt-monitors/#comments
www.webopedia.com/DidYouKnow/Hardware_Software/2005/all_about_monitors.asp
www.wisegeek.com/what-is-a-crt-monitor.htm
www.wikipedia.org/wiki/Cathode_ray_tube#Charactrons
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