How Does a Television Set Function?

by Contributing Writer


Television sets function using a device called the cathode ray tube (CRT). CRTs are instruments that actually display the images that appear on television screens. The cathode is a filament inside a glass tube. When it is heated, it attracts electrons from the ray within a vacuum created inside the tube. Other aspects of the television set that help it function include steering coils, phosphors and transmitted TV signals that actually dictate how beams are fired at the TV screen. Each of these factors work in concert to transmit images.

How the CRT Works

The cathode in a television set is an anode, which means that it is a positive energy source. Since electrons are negative, they are naturally attracted to the anode, which bounces the electrons off the cathode. This creates a process in which the electrons are tightened into an accelerated beam by the anode. The acceleration allows the electrons to shoot through the vacuum in the tube and hit the flat screen of the television set, located at the opposite end of the tube. Wrapped around the cathode ray tube are copper wires that generate magnetic fields within the tube. Once the beam of electrons pass through this field, it becomes highly concentrated, allowing the beam to move in a number of different directions (without the magnetic field, then the beam will only be concentrated in the center of the screen). This is done through different set of coils that move the beam vertically and horizontally.

How TV Phosphors Work

Phosphors are materials that emit light once they are struck by radiation. Ultraviolet light and electron beams are both radiated materials. The inside of all television sets are coated with phosphors. Phosphors come in three types of light: red, green, and blue. These lights are arranged in stripes or dots. The colors create the multitude of shades (there are thousands of combinations created in a phosphor that are determined by the color and how long the emission lasts after it has been discharged) seen on a color television set (black-and-white television sets only have one phosphor). When the electron beams strike the back of the television set, the phosphor emits lights that are converted into the colors being struck. The differences in hues and shades are caused by the primary colors located in the phosphors. Shadow masking is a technique in which tiny holes in a thin metal screen, which is located close to the phosphor coating, are lined up with the colored dots or stripes in the phosphors. Depending on signals the electron beam receives, certain beams will light certain dots (for instance, a blue beam strikes a blue dot) in the phosphor. To create a variation of colors, the red, green, and blue beams are fired in different combinations or fired or not fired at the same time to create white and black colors respectively.

How TV Signals Work

The electron beam is controlled by signals transmitted from TV stations or VCRs. This signal contains three important sources of information: intensity, horizontal-retrace signals and vertical-retrace signals. Each of these signals informs the TV set on when and how to move the electron beam across the face of the screen. Each signal is defined by the number of pulses it discharges to the beam of electrons. For instance, horizontal-retrace signals have 5-microsecond pulses at zero volts, with a variance at 0.5 (black) and 2.0 volts (white). The signal controls the intensity and, in a color TV set, has a 3.0 MHz bandwidth limitation. The vertical-retrace pulse, on the other hand, discharges 400 to 500 microsecond pulses. The pulse, which is serrated, is in sync with the beam as it crosses horizontally across the screen.