Linear Encoders

Linear encoders sense and digitize linear position change for positional measurement and feedback to control systems. Travel, encoder resolution, encoder accuracy, and lines or counts per distance are the most important performance specifications to consider. Travel or measurement range is the full range of travel that can be encoded. Some linear encoders have selectable or configurable measurement ranges. Encoder resolution is the smallest degree of distance measurement that linear encoders can make. Typically, this specification is set to different values within the same linear encoder. Encoder accuracy is a performance specification that accounts for variables such as linearity, hysteresis and temperature. Lines or counts per distance determines the minimum linear position increment that can be distinguished. Either counts or lines may be specified, but they are not the same; for example, in quadrature systems, a line is associated with four counts or pulses. 

There are two types of linear encoders and five types of encoder technologies. Absolute linear encoders provide a unique output signal for each mechanical position. They retain their position after power-down without requiring a home cycle. Incremental encoders provide output signals that repeat over the revolution. They do not retain their position after power-down since the outputs signals are not unique to any particular position. Choices for encoder technology are optical, magnetostrictive, magnetoresistive, and inductive. Optical encoders use a light emitter and receiver. Magnetostrictive encoders determine displacement or strain from the change in state of the magnetic field generated by a ferromagnetic material. Magnetoresistive linear encoders are made of nickel-iron thin-film on a silicon wafer and formed as a resistive strip. They are more sensitive than Hall effect sensors. Inductive encoders sense changes in a magnetic field and encode data into a position signal. Inductive technology is often suitable for harsh conditions or where contamination by dust is possible. Modular kit encoders, linear-to-rotary conversion, sealed encoders, and probe-style devices are also available. 

Absolute encoder code, incremental encoder signal, and electrical digital output are the main output specifications for linear encoders. There are three choices for absolute encoder code: gray, binary, and binary coded decimal (BCD). There are five choices for incremental encoder signal: digital (square wave), analog (sine / cosine), single channel, pulse and direction, and reference and index. Signal quadrature, a configuration in which two channels carry signals that are 90° out of phase, is also available. There are choices for electrical outputs, including analog current and analog voltage. Linear encoders can also use fiber optics, standard serial or parallel communication protocols, serial synchronous interface (SSI), FOUNDATION Fieldbus, controller area network bus (CANbus), INTERBUS^®, DeviceNet, PROFIBUS^®, Ethernet, serial real-time communications system (SERCOS), and SUCOnet. INTERBUS is a registered trademarks of Phoenix Contact GmbH & Co. PROFIBUS is a registered trademark of PROFIBUS International.

• Linear Encoders
  A typical linear encoder consists of a scanning unit and a scale. The scale is generally glass and is cemented to a support, usually an aluminum extrusion. The scanning unit contains a light source,...
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• Optical Linear Encoders
  Optical linear encoders use a light emitter and receiver to achieve incremental linear counting. The outputs are sine-cosine waves or digitized square waves. Configurations for optical linear encoders...
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• Linear Encoders - Out With Glass, In With Steel
  Rotary and linear encoders are standard equipment in today's automated motion systems. Both types, generally, are optically based, relying on light passing through or reflecting off a scale and then...
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Part Numbers for Linear Encoders