How to Choose a Rotary Encoder for an Automation Project


If you need to purchase an encoder but are unsure which type is best, get assistance from a reputable source. That way, you’ll receive accurate and reliable information on the count, direction, speed, and position capabilities based on your specific application. For automation projects, many people prefer optical rotary encoders.

Before you buy a rotary encoder, take time to learn how the two best types differ and the benefits they provide.

Optical Vs. Magnetic Rotary Encoder

Before going over the buying tips provided, look at the brief rundown between these two rotary types.


With a spinning magnetized disc composed of alternating poles and either a magneto-resistive or half-effect sensor, the magnetic rotary encoder detects changes within magnetic flux fields. Since it’s rugged and handles both vibration and shock with ease, it’s a good option for your automation project.


Compared to the magnetic type, optical rotary encoders boast higher resolution and accuracy. Along with a glass or plastic disc, this device consists of an LED light and several slots that alternate between opaque and transparent. If you want an encoder that can detect motion and provide accurate information, this is likely the one you want.

Helpful Tips When You’re Ready to Buy a Rotary Encoder

Both an optical and magnetic rotary encoder affect motor performance. So, have one of your company’s engineers look at the various properties of each, in particular, those listed below.

  • Audible noise (the quieter, the better)
  • Bandwidth (this determines the response of the drive command signal)
  • Positioning accuracy
  • Power loss
  • Speed stability

To better understand the importance of this, whether you choose an optical or magnetic rotary encoder, consider a few examples of why these properties matter.

Position Accuracy

Unfortunately, a magnetic rotary encoder has significant limitations. Typically, the position accuracy of this device falls within a range of ~ ±500”, which equates to 16,384 positions per revolution. In comparison, the optical device has a much greater accuracy of ~ ±280”, resulting in 131,072 positions per revolution.

If accurate positioning is critical to your automation project, the optical encoder wins hands down.

Speed Stability

This is another important factor to look at before you buy a rotary encoder. Along with the number of measuring steps per revolution, the engineer should focus on signal quality. There’s a reason for this. The way an encoder achieves the resolution needed is by having interpolated scanning signals. So, high quality is essential.


Finally, there’s bandwidth as it relates to the control reliability and command response. To ensure optimal performance, whether an optical or magnetic rotary encoder, the engineer should look at two specific things. First is the rigidity of the coupling that goes between the encoder shaft and motor shaft. The second has to do with mounting. If not done properly, that can cause long-term resonant vibration.

We Can Help You Find the Ideal Product

When you’re ready to buy a rotary encoder, contact us at Maintenance Diagnostic Systems, Inc. Not only do we supply the different types of encoders, but we can also assist with various services.

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