TV

Television is a widely used telecomunication medium for sending (broadcasting) and receiving moving images, either black and white”) or color , usually accompanied by sound. “Television” may also refer specifically to a television set, television programming or television transmission. The word is derived from mixed latin and greek roots, meaning “far sight”. Since late 1930, the television set has become a common communications receiver in homes, businesses and institutions, particularly as a source of entertainment and news. Since the 1970s, recordings on video cassette, and later, digital media such as DVD, have resulted in the television frequently being used for viewing recorded as well as broadcast material.

A standard television set comprises multiple internal electronic circuits, including those for tuning and decoding broadcast signals. A display device which lacks these internal circuits is therefore properly called a monitor, rather than a television. A television set may be designed to handle other than traditional broadcast or recorded signals and formats, such as closed circuit television (CCTV), digital television (DTV) and high definition television (HDTV).

Around the globe, broadcast television is financed by either government, advertising, licensing (a form of tax), subscription or any combination of these. To protect revenues, subscription TV channels are usually encrypted to ensure that only subscription payers receive the decryption codes to see the signal. Non-encrypted channels are known as free to air.

DVD

Digital Versatile Disk/DVD is a popular optical disc storage media format. Its main uses are video and data storage. Most DVDs are of the same dimensions as compact discs but store more than six times as much data.

The basic types of DVD are referred to by a rough approximation of their capacity in gigabytes.

The 12 cm type is a standard DVD, and the 8 cm variety is known as a mini DVD. These are the same sizes as a standard CD and a mini CD, respectively. The capacity by surface (MiB/cm²)differs from 6.92MiB/cm² in the DVD-1 to 18.0 MiB/cm² in the DVD-18

DVD uses 650nm wavelength laser diode light as opposed to 780 nm for CD or 405 nm for HD-DVD or Blu-ray Disc. This permits a smaller pit to be etched on the media surface (1.32 µm for DVD versus 1.6 µm for CD) compared to CDs.

Writing speeds for DVD were 1×, that is 1350 kB/s (1318 KIB/s), in the first drives and media models. More recent models at 18× or 20× have 18 or 20 times that speed. Note that for CD drives, 1× means 150 KIB/s (153.6 kB/s), approximately 9 times slower.

DVD recordable discs supporting this technology are backward compatible with some existing DVD players and DVD-ROM drives^. Many current DVD recorders support dual-layer technology, and the price is now comparable to that of single-layer drives, though the blank media remains more expensive. The recording speeds reached by dual-layer media are still well below those of single-layer media.

There are two modes for dual layer orientation. With parallel track path (PTP), used on DVD-ROM, both layers start at the inside diameter (ID) and end at the outside diameter (OD) with the lead-out. With opposite track path (OTP), used on DVD-Video, the lower layer starts at the ID and the upper layer starts at the OD, where the other layer ends, they share one lead-in and one lead-out

MP3

MPEG-1 Audio Layer 3 more commonly referred to as MP3,is a digital audio encoding format using a form of lossy data compression. It is a common audio format for consumer audio storage, as well as a de facto standard encoding for the transfer and playback of music on digital audio players. MP3 is an audio-specific format that was designed by the Motion Pictures Expert Group. A group formed by several teams of engineers at Fraunhofer in Erlangen,Germany, AT&T Bell Lab in Murray Hill, NJ, USA, Thomson-Brandt, and CCETT as well as others. It was approved as an ISO standard in 1991.

The use in MP3 of a lossy compression algorithm is designed to greatly reduce the amount of data required to represent the audio recording and still sound like a faithful reproduction of the original uncompressed audio for most listeners, but is not considered high fidelity audio by audiophiles. An MP3 file that is created using the mid-range bit rate setting of 128 kbit/s will result in a file that is typically about 1/10th the size of the CD file created from the original audio source. An MP3 file can also be constructed at higher or lower bit rates, with higher or lower resulting quality. The compression works by reducing accuracy of certain parts of sound that are deemed beyond the auditory resolution ability of most people. This method is commonly referred to as perceptual coding. It internally provides a representation of sound within a short term time/frequency analysis window, by using pscyoacoustic models to discard or reduce precision of components less audible to human hearing, and recording the remaining information in an efficient manner. This is relatively similar to the principles used by JPEG, an image compression format.

DC and AC Motor

A DC motor is designed to run on DC electric power. Two examples of pure DC designs are Michael Faraday's homopolar motor(which is uncommon), and the ball bearing motor , which is (so far) a novelty. By far the most common DC motor types are the brushed and brushless types, which use internal and external commutation respectively to create an oscillating AC current from the DC source -- so they are not purely DC machines in a strict sense.

In 1882, Nikola Tesla invented the rotating magnetic field, and pioneered the use of a rotary field of force to operate machines. He exploited the principle to design a unique two-phase induction motor in 1883. In 1885, Galileo Ferraris independently researched the concept. In 1888, Ferraris published his research in a paper to the Royal Academy of Sciences in Turin.

Introduction of Tesla's motor from 1888 onwards initiated what is sometimes referred to as the Second Industrial Revolution, making possible the efficient generation and long distance distribution of electrical energy using the alternating current transmission system, also of Tesla's invention (1888). Before the invention of the rotating magnetic field, motors operated by continually passing a conductor through a stationary magnetic field (as in homopolar motors).

Tesla had suggested that the commutators from a machine could be removed and the device could operate on a rotary field of force. Professor Poeschel, his teacher, stated that would be akin to building a perpetual motion machine.

Universal Motor

A variant of the wound field DC motor is the universal motor. The name derives from the fact that it may use AC or DC supply current, although in practice they are nearly always used with AC supplies. The principle is that in a wound field DC motor the current in both the field and the armature(and hence the resultant magnetic fields) will alternate (reverse polarity) at the same time, and hence the mechanical force generated is always in the same direction. In practice, the motor must be specially designed to cope with the AC (impedance must be taken into account, as must the pulsating force), and the resultant motor is generally less efficient than an equivalent pure DC motor.

Operating at normal power line frequencies, the maximum output of universal motors is limited and motors exceeding one kilowatt (about 1.3Horse power) are rare. But universal motors also form the basis of the traditional railway traction motor in electric railways . In this application, to keep their electrical efficiency high, they were operated from very low frequency AC supplies, with 25 and 16.7 hertz (Hz) operation being common. Because they are universal motors, locomotives using this design were also commonly capable of operating from a third rail powered by DC.

The advantage of the universal motor is that AC supplies may be used on motors which have the typical characteristics of DC motors, specifically high starting torque and very compact design if high running speeds are used. The negative aspect is the maintenance and short life problems caused by the commutator. As a result such motors are usually used in AC devices such as food mixers and power tools which are used only intermittently. Continuous speed control of a universal motor running on AC is easily obtained by use of a thyristor circuit, while stepped speed control can be accomplished using multiple taps on the field coil. Household blenders that advertise many speeds frequently combine a field coil with several taps and a diode that can be inserted in series with the motor (causing the motor to run on half-wave rectified AC).

Universal motors generally run at high speeds, making them useful for appliances such as blenders, vacuum cleaners and hair dryerswhere high RPM operation is desirable. They are also commonly used in portable power tools, such as drills, circular and jig saws, where the motor's characteristics work well. Many vacuum cleaner and weed trimmer motors exceed 10,000 RPM, while Dremel and other similar miniature grinders will often exceed 30,000 RPM.

Motor damage may occur due to overspeeding (running at an RPM in excess of design limits) if the unit is operated with no significant load. On larger motors, sudden loss of load is to be avoided, and the possibility of such an occurrence is incorporated into the motor's protection and control schemes. In smaller applications, a fan blade attached to the shaft often acts as an artificial load to limit the motor speed to a safe value, as well as a means to circulate cooling airflow over the armature and field windings.

With the very low cost of semicobductor rectifiers, some applications that would have previously used a universal motor now use a pure DC motor, sometimes with a permanent magnet