#CATHODE RAY TUBE TV#

#CATHODE RAY TUBE TV#

In TV and computer monitors, prior to the advent of flat-screen (mostly LCD) technology, the phosphor-coated inside of the CRT screen was scanned in a fixed pattern known as the raster. Without the gas ions, this beam was more controllable, and in conjunction with a phosphor coating, all that remained to make a CRT for use in an oscilloscope were internal deflection plates and for TV, external deflection coils.

Around 1904, the Crookes tube evolved into a purely electronic vacuum tube in which a hot cathode, heated by an adjacent low-voltage filament, produced a stream of electrons by means of thermionic emission. In 1895, Wilhelm RГ¶ntgen detected X-rays emanating from the Crookes tube, immediately suggesting medical and diagnostic applications. After striking the wall, the electrons returned to the anode, flew back through the attached conductor and power supply returning to the cathode. Next, researchers applied a phosphor coating to the inside of the glass wall, enhancing visibility and creating persistence. Falling back, these electrons emitted photons, a glow, visible outside the glass envelope.

They collided with atoms in the glass, knocking orbiting electrons into higher-energy shells. The beam, traveling at approximately 20% of the speed of light, and many of the electrons flew past the anode, striking the tubeвЂ™s end wall. Upon impact, additional electrons were released, combining with and intensifying the beam. These energized particles collided with other gas molecules, freeing more electrons and converting the molecules to positive ions, which were attracted back toward the cathode. The resulting field accelerated electrically charged ions and electrons present in the residual gas. A dc voltage up to 100 kV was applied between the cathode and an anode at the far end of the tube. In the Crookes tube, electrons were generated by the ionization of low-pressure air surrounding the cathode. Thompson identified them as streams of negative particles, later named вЂњelectrons.вЂќ (The original Crookes tube was a cold-cathode device.) Numerous researchers investigated, wrote and lectured on the properties of these cathode rays. Later when the hot cathode was introduced, the vacuum was additionally needed so the incandescent filament heating the cathode would not burn out. The vacuum was necessary so electrons could travel unimpeded. The Crookes tube, developed in England in the 1870s, consisted of a glass envelope from which air was partially evacuated. In 1890 it was found that cathode rays could be deflected by an electrostatic field and William Crookes demonstrated cathode ray deflection by magnetic fields. Generated within a vacuum tube, cathode rays cast shadows on the glass wall, indicating they traveled in straight lines. Cathode rays were discovered in the late 19th century, right around the time James Clerk Maxwell found that light was a form of electromagnetic radiation. (CRT material and process technologies are still common in the vacuum tube industry as a whole where they find use in products such as incandescent, fluorescent, and high-power arc lamps microwave, traveling wave, and high-power amplifier tubes, x-ray tubes, and magnetrons for heating.)Д«ut itвЂ™s worth taking a close look at the CRT, particularly in the oscilloscope. Today, except for a few educational models and replacements for radar installations, CRTs arenвЂ™t used as displays. A few decades ago, virtually all computer monitors, radar installations, TVs and oscilloscopes employed cathode ray tubes for the userвЂ™s visual interface.

Cathode ray tube