many kinds of encoder

There are many kinds of encoders and feedback devices. There are resolvers, encoders, glass scales, interferometer scales, inductive scales, capacitive scales, pulse coders, rotary-linear encoders, and even mechanical-hydraulic encoders.  There are temperature specific scales and zero temperature scales. Each type of scale has its specific application and price. Also any type of scale can only perform at its best if installed, adjusted and maintained correctly.

How to Choose an Encoder for Harsh Environments

In industrial automation and motion control applications, selecting the proper encoder technology is key to maximizing performance. Optical or magnetic, which to choose?

Optical encoders perform well in clean environments, but what about those that are dirty, hot, humid or subject to high levels of vibration? Are magnetic encoders a better option in those cases? Let’s take a closer look at each.

Optical Encoder Technology

• Optical encoders pass a beam of light through a series of windows in a rotating disk. Any contamination that impedes the light source will cause encoder failure. This includes condensation from fluctuating humidity and temperature.
• Optical encoders require a precise, small air gap, often less than 0.25 mm (0.010 in.). As a result, they not only require very small shaft end play but they are vulnerable to shock and vibration.
• Because of their need for a clean, protected environment, they often are protected by an expensive, bulky package to help isolate them from the elements.

Magnetic Encoder Technology

• Magnetic sensing does not need a clean, transparent gap. Dirt, dust, oil, condensation and other non-ferrous contaminants do not affect their reliability.
• Magnetic encoders also are inherently shock- and vibration-resistant. The sensor-to-target gap is large compared to that of an optical encoder, and can be as large as 4 mm (0.157 in.). They can handle shaft end play as high as 2.5 mm (0.98 in.) total.
• Modular magnet encoders do not require an expensive, ruggedized package because the magnetic technology can handle dirty and harsh environments up to 135° C (275° F). Digital quadrature output signals are the same as in an optical encoder and their accuracy is sufficient for most applications where optical encoders are typically used.

The Most Attractive Choice

Magnetic encoders offer a number of clear advantages over optical encoders including:

• Greater durability
• Higher reliability
• Compact packaging
• Much larger gap tolerances
• Higher temperature range
• Harsh environment operation
• Higher vibration and shock tolerance

When selecting the proper encoder technology for an application, engineers should consider environmental, packaging, resolution and cost requirements. In cases where performance requirements can’t be compromised and the operating environment could be challenging, magnetic encoder technology can meet a customer’s needs at a relatively low cost.