Encoder

An encoder is a technical element. Here, the term appear both in communications technology as well as in drive technology and have different meanings.

Encoder in communication engineering

One understands in communications technology under an encoder (English Encoder) is usually the first converter, converter or transformer for analogue or digital signals. It forms with possible further converters and a decoding unit, and decoder (English Decoder) called a logical unit or a functional sequence.

Encoder in digital communications technology

An encoder is a system comprising a data source ( for example a digital audio signal, a file format, a computer image, a data signal which is sensitive to errors ) is converted into a suitable format for a particular channel.

An encoder operates on a fixed predetermined coding scheme to allow the decoder at the receiver side, the signal can convert back to the original format again.

For an encoder always contains an " opposite " working decoder. One unit of encoder and decoder is called a codec.

There are many reasons for the coding of a data source:

• Compress audio or video data for a quick transferability on "slow" data channels ( number of data in a short time )
• Compressing audio or video data in order to achieve higher image quality or sound quality at a given bit rate or a given space.
• Data is encoded with error protection to prevent disturbances occurring on the transmission channel and interfere with the data would be corrected by the recipient ( Forward Error Correction). For this purpose, the original data is accompanied by an encoder additional information that allows the decoder to separate data and error of each other.

Encoder in the analog communications technology

Before broadcasting stereo audio signals are encoded in the transmitter and decoded to two-channel stereo signal at the reception in radio receiver through the Stereodekodierer again.

Other examples are the analog color encoding system within a black and white video frequency band ( NTSC, SECAM and PAL), and the multi-frequency (DTMF ) to the number transmission over telephone lines.

Mixed forms are the pulse rate modulation, which generates an analog signal proportional to the frequency, and the pulse position and pulse width modulation.

Encoder for mechanical movements

Encoder for signal formation of movements operate optically, magnetically or mechanically with contacts. There are sensors or input devices, which detect the current position of a shaft or a drive unit and outputting an electrical signal. There are two types of encoders: Rotary and linear encoders. Rotary encoders are mounted on rotating components, for example on a motor shaft. Linear encoders are typically mounted to components in a straight line.

Incremental encoder have to be counted or absolute measuring standards as a dash pattern (light barrier), magnetization or contacts. In the case of a permanent magnetization, the magnetic field modulation can be evaluated by means of AMR, GMR, Hall sensors, or inductive sensors. For incremental inductive sensors often enough also a non-magnetic teeth.

Absolute position encoders operate on the basis of material measures that assign a unique signal pattern of each position (see absolute encoder).

Not absolute measurement encoder is referred to as incremental. They are used on motor shafts, but also as an input device to digitally operated devices to (eg the volume ) to be set or control of hand motor movements (for example, to CNC controls ).

With the help of the output signal of an encoder, a so -equipped drive unit to perform reproducible movements and - in the case of an absolute encoder - even after switching off the machine again just go to the home position (reference position). Incremental need to prospect the reference position an additional donor, such as a limit switch. An example of a linear encoder is optically operating scanning a applied to a strip line pattern in a printer which allows the carriage to carry out a defined movement along the line.