Coders in communications engineering
In communications engineering , an encoder is generally understood to be the first converter , converter or converter for digital or analog signals . Together with possible further converters or a decoding unit, also called a decoder , it forms a logical unit or a function chain.
Encoders in digital communications
An encoder works according to a fixed coding rule so that the decoder on the receiver side can convert the signal back into the original format.
A coder therefore always has an "oppositely" working decoder. A unit consisting of an encoder and a decoder is called a codec .
There are many reasons for coding a data source:
- Compression of audio or video data for fast transferability via "slow" data channels (a lot of data in a short time)
- Compression of audio or video data in order to achieve a higher picture or sound quality with a given transmission speed or given storage space.
- Data is encoded with error protection so that interference that occurs on the transmission channel and that would interfere with the data can be corrected at the receiver ( Forward Error Correction ). For this purpose, additional information is added to the original data by an encoder, which allows the decoder to separate data and errors from one another.
Coders in analog communications engineering
Further examples are the analog processes for color transmission within a black and white video frequency band ( NTSC , SECAM - and PAL ), as well as the multi-frequency dialing process (MFV) for the transmission of numbers over telephone lines.
Encoder for mechanical movements
Encoders for generating signals from movements work optically, magnetically or mechanically with contacts. They are transducers or input devices that recognize the current position of a shaft or a drive unit and output it as an electrical signal. There are two types of encoders: rotary and linear encoders. Rotary encoders or rotary encoders are mounted on rotating components, for example on a motor shaft. Linear encoders are typically mounted on components with straight movements.
Encoders have incremental, to be counted or absolute measuring standards as line patterns ( light barrier ), magnetization or contacts. In the case of permanent magnetization , the magnetic field modulation can be evaluated using AMR , GMR , Hall sensors or inductive sensors. Non-magnetic teeth are often sufficient for incremental inductive sensors.
Absolute encoders work on the basis of material measures that assign a unique signal pattern to each position (see absolute encoder ).
Encoders that do not measure absolutely are called incremental encoders . They are used on motor shafts, but also as input devices on digitally operating devices to set parameters (e.g. volume) or to control motor movements by hand ( e.g. on CNC controls).
With the help of the output signal of an encoder, a drive unit equipped with it can carry out reproducible movements and - in the case of an absolute encoder - move back exactly to the starting position (reference position) even after the machine has been switched off. Incremental encoders require an additional encoder, for example a limit switch, to find the reference position. An example of a linear incremental encoder is the optical scanning of a line pattern applied to a strip in a printer, which allows the print carriage to perform a defined movement along the line.
- Manfred Rost, Sandro Wefel: Electronics for computer scientists. From the basics to microcontroller application, De Gruyter Verlag, Oldenbourg 2013, ISBN 978-3-4867-0692-5 .
- Wulf Alex, Gerhard Bernör: UNIX, C and Internet. Modern data processing in science and technology, Springer Verlag, Berlin / Heidelberg 1994, ISBN 978-3-540-57881-9 .
- Ralf Steinmetz: Multimedia technology. Basics - Components and Systems, 3rd edition, Springer Verlag, Berlin / Heidelberg 2000, ISBN 978-3-642-63539-7 .