Understanding Resolution in optical and magnetic Encoders

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Grayhill offers a wide range of optical encoders

Where Vishay favours magnetic encoders; Grayhill offers a very wide range of optical encoders. These, like the Bourns’ optical encoders, are 2-bit, incremental, quadrature code output devices. In the MMI area, Avnet Abacus carries for example the 61K and 63K models, which represent the low- and high-end performance options in terms of speed and life cycles.

Both feature 4-pin connections and resolution up to 256 positions / revolution but the 61K is a 300 rpm part, specified for 10 million cycles, while the 63K uses ball bearings to achieve 5,000 rpm and 300 million cycles.

While this article mainly covers MMI products, we should mention that Grayhill offers one of the broadest spectrums of optical HMI solutions, including highly integrated components like the NavCoder and the Multiturn Ring Encoder.

Last but not least will be the cost consideration

Rotary encoders are used to measure angular position or speed for control and feedback purposes across a wide range of applications, spanning industrial, automotive, medical and consumer. Modern designs favour non-contact sensing methods, either magnetic or optical, for improved reliability, performance and life expectancy.

In practice we find the optical types cover the requirement for incremental, quadrature output signals to simply measure position change or rotational speed, while it is the magnetic types that typically provide absolute position information. Although not a fundamental limitation in the design of optical encoders, none of the models considered offer more than 256-position (8-bit) resolution whereas the magnetic types feature 10- and 12-bit resolution models.

Beyond this, the differentiation lies in the maximum speed and life expectancy of the encoder (primarily determined by bearing type), other environment factors (e.g. temperature range) and physical attributes such as their dimensions, electrical terminals and ruggedness (shock, vibration, etc.). Last but not least will be the cost consideration – clearly high performance, long life and ruggedness all come at a price.

* Giovanna Monari is Senior Product Manager E-Mech, Avnet Abacus

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