Rotary encoders, also known as shaft encoders, are high-speed devices used to monitor or control the angular position of a rotating mechanism (axle, shaft, etc.). This capability is extremely valuable for a broad range of markets, with many proven consumer, industrial, and research applications.

TT Electronics is an industry-leading supplier of ultra-precise rotary encoders. We provide both contact and non-contacting solutions for continuous revolution monitoring and control. In this article, we aim to cover all the basics of rotary encoders, from their working principles to the different types available today.

How Does a Rotary Encoder Work?

Electronically tracking the rotation of an axle or shaft can be extremely challenging. This difficulty increases commensurately in-line with higher precision demands, for instance, tracking mere fractions of a single rotation. The solution is to ‘encode’ those revolutions into a sensing element which generates a relative electrical signal output.

Mechanical rotary encoders typically comprise a disk mounted radially on a rotatable shaft or bushing (hollow shaft). The disk is evenly patterned so that a sensing element within the housing can continuously generate a binary signal for each possible angle of rotation on the shaft. A single contact pin, photodiode, or magnet (depending on the type of encoder used) would generate a pure binary code, which leaves room for measurement inaccuracies.

The reflected binary code (RBC), widely referred to as the Gray code, was developed to improve error correction in electromechanical transducers such as rotary encoders. This involves multiple tracks and contact elements or detectors to provide an output of 2-bits or greater, thus eliminating false readings. 

Types of Rotary Encoders

Rotary encoders are most often divided into two overarching subgroups: Absolute and incremental encoders. However, before exploring the difference between those two encoder types, it is worth taking a broad view of the different sensing technologies used.

  • Mechanical rotary encoders: Use conductive metal segments on an insulating disk with individual contact pins per track.
  • Optical rotary encoders: Use a photodiode and slit disk, an opaque disk with transparent sections, or a disk with reflective segments to measure rotation via on/off optical signals.
  • Magnetic rotary encoders: Use Hall Effect sensors and a series of magnetic poles to transmit shaft rotation as a function of the magnetic pole position.

Difference Between Absolute and Incremental Encoders

The difference between absolute and incremental rotary encoders is the output signal. Absolute rotary encoders measure angular positions and can provide continuous position monitoring even following periods of no power. Incremental encoders can calculate angular position – provided power is not interrupted – as well as speed and distance. The resolution of each rotary encoder type is based on the number of pulses per revolution, but an incremental encoder refers to the signal output of a single revolution while an absolute encoder uses an address count.

Rotary Encoders from TT Electronics

TT Electronics supplies a broad range of compact encoders based on mechanical-type contacts and 2-bit Gray code. With extended operating life cycles and a choice of switch features, our rotary encoders are suitable for a broad range of application areas from appliances to audio control to navigation systems.

Explore our datasheets for our full EN series of rotary encoders. Or, contact a member of the TT Electronics sales team with any direct queries.


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