Cathode Ray Tube (CRT) Monitors

CRT stands for cathode ray tube, describing the technology inside an analog computer monitor or television set. A CRT monitor or TV is readily recognizable by its bulky form. LCD monitors and plasma television sets, or flat panel displays, use newer digital technologies. (http://www.wisegeek.com/what-is-a-crt-monitor.htm)

The most important component in the monitor is the picture tube, also called a cathode ray tube or CRT. The CRT is what makes the image that you see on the screen, and its characteristics primarily determine the quality of the image you see. A good monitor will always have a good CRT; no amount of fancy controls and other features can make up for a bad tube. In fact, the CRT defines the whole monitor so much that often the monitor is just called "the CRT". (http://www.pcguide.com/ref/crt/crt.htm)

CRT, it's generally agreed that German scientist Karl Ferdinand Braun developed the first controllable CRT in 1897, when he added alternating voltages to the device to enable it to send controlled streams of electrons from one end of the tube to the other. (http://www.pctechguide.com/42CRTMonitors.htm)

The CRT monitor comes in 15-inch to 21-inch sizes (38 — 53 cm) and larger, though the actual viewing screen is about 1 inch (2.5 cm) smaller than the rated size. Screens are measured diagonally from corner to corner, including the case. (http://www.wisegeek.com/what-is-a-crt-monitor.htm)

Tried, true, dependable and economical, CRT technology ruled for decades before its dethroning in the late 1990s - early 2000s. Negatives of the CRT include radiation emission, high power consumption, weight and bulk. (http://www.wisegeek.com/what-is-a-crt-monitor.htm)

How does it work?

A CRT works by moving an electron beam back and forth across the back of the screen. Each time the beam makes a pass across the screen, it lights up phosphor dots on the inside of the glass tube, thereby illuminating the active portions of the screen. By drawing many such lines from the top to the bottom of the screen, it creates an entire screenful of images. (http://www.webopedia.com/TE

RM/C/CRT.html)

Most CRT monitors have case depths about as deep as the screen is wide, begging the question "what is it that's inside a monitor that requires as much space as a PC's system case itself?" (http://www.pctechguide.com/42CRTMonitors_Anatomy.htm)

A CRT is essentially an oddly-shaped, sealed glass bottle with no air inside. It begins with a slim neck and tapers outward until it forms a large base. The base is the monitor's "screen" and is coated on the inside with a matrix of thousands of tiny phosphor dots. Phosphors are chemicals which emit light when excited by a stream of electrons: different phosphors emit different coloured light. Each dot consists of three blobs of coloured phosphor: one

red, one green, one blue. These groups of three phosphors make up what is known as a single pixel. (http://www.pctechguide.com42CRTMonitors_Anatomy.htm)

In the "bottle neck" of the CRT is the electron gun, which is composed of a cathode, heat source and focusing elements. Colour monitors have three separate electron guns, one for each phosphor colour. Images are created when electrons, fired from the electron guns, converge to strik

e their respective phosphor blobs. (http://www.pctechguide.com/42CRTMonitors_Anatomy.htm)

Convergence is the ability of the three electron beams to come together at a single spot on the surface of the CRT. Precise convergence is necessary as CRT displays work on the principal of additive coloration, whereby combinations of different intensities of red green and blue phosphors create the illusion of millions of colours. When each of the primary colours are added in equal amoun

ts they will form a white spot, while the absence of any colour creates a black spot. Misconvergence shows up as shadows which appear around text and graphic images. (http://www.pc

techguide.com/42CRTMonitors_Anatomy.htm)

The electron gun radiates electrons when the heater is hot enough to liberate electrons (negatively charged) from the cathode. In order for the electrons to reach the phosphor, they have first to pass through the monitor's focusing elements. While the radiated electron beam will be circular in the middle of the

screen, it has a tendency to become elliptical as it spreads its outer areas, creating a distorted image in a process referred to as astigmatism. The focusing elements are set up in such a way as to initially

focus the electron flow into a very thin beam and then - having corrected for astigmatism - in a specific direction. This is how the electron beam lights up a specific phosphor dot, the electrons being drawn toward the phosphor dots by a powerful, positively charged anode, located near the screen. (http://www.pctechguide.com/42CRTMonitors_Anatomy.htm)

The deflection yoke around the neck of the CRT creates a magnetic field which controls the direction of the electron beams, guiding them to strike the proper position on the screen. This starts in the top left corner (as viewed from the front) and flashes on and off as it moves across the row, or "raste

r", from left to right. When it reaches the edge of the screen, it stops and moves down to the next line. Its motion from right to left is called horizontal retrace and is timed to coincide with the horizontal blanking interval so that the retrace lines will be invisible. The beam repeats this process until all lines on the screen are traced, at which point it moves from the bottom to the top of the screen - during the vertical retrace interval - ready to display the next screen image. (http://www.pctechguide

.com/42CRTMonitors_Anatomy.htm)

Since the surface of a CRT is not truly spherical, the beams which have to travel to the center of the display are foreshortened, while those that travel to the corners of the display are comparatively longer. This means that the period of time beams are subjected to magnetic deflection varies, according to their direction. To compensate, CRT's have a deflection circuit which dynamically varies the deflection current depending on the position that the electron beam should strike the CRT surface. (http://www.pctechguide.com/42CRTMonitors_Anatomy.htm)

Before the electron beam strikes the phosphor dots, it travels thorough a perforated sheet located directly in front of the phosphor. Originally known as a "shadow mask", these sheets are now available in a number of forms, designed to suit the various CRT tube technologies that have emerged over the years. They perform a number of important functions:

• they "mask" the electron beam, forming a smaller, more rounded point that can strike individual phosphor dots cleanly
• they filter out stray electrons, thereby minimising "overspill" and ensuring that only the intended phosphors are hit
• by guiding the electrons to the correct phosphor colours, they permit independent control of brightness of the monitor's three primary colours.

When the beam impinges on the front of the screen, the energetic electrons collide with the phosphors that correlate to the pixels of the image that's to be created on the screen. When this happens each is illuminated, to a greater or lesser extent, and light is emitted in the colour of the individual phosphor blobs. Their proximity causes the human eye to perceive the combination as a single coloured pixel. (http://www.pctechguide.com/42CRTMonitors_Anatomy.htm)

Who are the leading providers for the said device?

By 2001, thewriting was clearly on the wall and the CRT's long period of dominance appeared finally to be coming to an end. In the summer of that year Philips Electronics - the world's largest CRT manufacturer - had agreed to merge its business with that of rival LG Electronics, Apple had begunshipping all its systems with LCD monitors and Hitachi had closed its $500m-a-year CRT operation, proclaiming that "there are no prospects for growth of the monitor CRT market". Having peaked at a high of approaching $20 billion in1999, revenues from CRT monitor sales were forecast to plunge to about half that figure by 2007. (http://www.pctechguide.com/42CRTMonitors.htm)

How does it differ from other similar devices?

Whilst competing technologies - such as LCDs and PDPs had established themselves in specialist areas, there are several good reasons to explain why the CRT was able to maintain its dominance in the PC monitor market into the new millennium:

• phosphors have been developed over a long period of time, to the point where they offer excellent colour saturation at the very small particle size required by high-resolution displays
• the fact that phosphors emit light in all directions means that viewing angles of close to 180 degrees are possible
• since an electron current can be focused to a small spot, CRTs can deliver peak luminances as high as 1000 cd/m² (or 1000 nits)
• CRTs use a simple and mature technology and can therefore be manufactured inexpensively in many industrialised countries
• whilst the gap is getting smaller all the time, they remain significantly cheaper than alternative display technologies.

(http://www.pctechguide.com/42CRTMonitors.htm)

What is the device used for?

While many scientists were busy trying to unlock the secrets of cathode rays, others were searching for ways to apply them toward practical ends. The first such application came in 1897 in the form of Karl Ferdinand Braun's oscilloscope. This device used a cathode ray tube to produce luminescence on a chemically treated screen. The cathode rays were allowed to pass through a narrow aperture, effectively focusing them into a beam which appeared on the screen as a dot. The dot was then made to "scan" across the screen according to the frequency of an incoming signal. An observer viewing the oscilloscope's screen would then see a visual representation of an electrical pulse. (http://www.discoveriesinmedicine.com/Bar-Cod/Cathode-Ray-Tube-CRT.html)

During the first three decades of the twentieth century, inventors continued to devise uses for cathode ray technology. Inspired by Braun's oscilloscope, A. A. Campbell-Swinton suggested that a cathode ray tube could be used to project a video image upon a screen. Unfortunately, the technology of the time was unable to match Campbell-Swinton's vision. It was not until 1922 that Philo T. Farnsworth used a magnet to focus a stream of electrons onto a screen, producing a crude image. Though the first of its kind, Farnsworth's invention was quickly superseded by Vladimir Zworykin's kinescope, the ancestor of the modern television.( http://www.discoveriesinmedicine.com/Bar-Cod/Cathode-Ray-Tube-CRT.html)

Most forms of image-viewing devices are based upon cathode-ray technology. In addition, electron guns are used widely in scientific and medical applications. One important use for cathode-ray research has been the electron microscope, invented in 1928 by Ernst Ruska. The electron microscope uses a stream of electrons to magnify an image. Because electrons have a very small wavelength, they can be used to magnify objects that are too small to be resolved by visible light. Just as Plucker and Crookes did, Ruska used a strong magnetic field to focus the electron stream into an image. (http://www.discoveriesinmedicine.com/Bar-Cod/Cathode-Ray-Tube-CRT.html)

Today, CRT is known as the technology used in most televisions and computer display screens. (http://www.webopedia.com/TERM/C/CRT.html)

Are there other possible uses for the device aside from what it is designed for?

Since CRT monitors are already being phased out because of the launch of various flat screen alternatives, the following strategies have been developed to recycle and compromise lead, barium and strontium glass:

1. Recycle as much as possible back to the crt production. However this might be rather limited (possibly <100kt)>
2. Feed as much as possible to the smelting industry (e.g. flux in lead smelters)
3. The rest should, adhering to the non-dillution principle, be stored for possible future use. Probably a segregation and cleaning could be applied but maybe thats not even necessary. In the case of Switzerland this would imply a store room of ca. 30mx100mx10m (assuming there is no further crt glass coming in (which is the case since 2007), no recycling (currently 90%, a current stock of 100kt and a density of 3t/m3 (my estimates))
4. There might be more options such as www.nulifeglass.com who separate lead from the glass in thermal/electrolytic process. Considering current lead prices this might be an interesting option too

(http://ewasteguide.info/forum/future_crt_strategy)