How to Specify Accuracy and Resolution for Your Encoder

Resolution and accuracy are often over-specified, frequently due to a lack of understanding of the differences between them. Here’s some help in knowing the difference.

Resolution and Accuracy Explained
Encoders provide a number of evenly spaced clicks or positions per revolution. Resolution is the number of positions in a revolution (examples: 500, 1,000 or 5,000). Accuracy (or error) defines how close each of those reported transitions is compared to its ideal position. This error is specified in mechanical arc minutes or arc seconds. The following illustrations demonstrate the differences:

Many take the route of “better safe than sorry” and, as a result, over-specify resolution and accuracy. There are downsides to doing this. For example, too much resolution can overload the electrical system. And over-specifying either resolution or accuracy can increase your costs.

Which Technology?

While optical encoders provide high resolution and accuracy, they typically are more vulnerable to harsh environments. 
  • New advancements in magnetic encoding technology have resulted in the development of compact, low-cost encoders that are more tolerant of harsh, dirty operating environments. However, on-axis magnetic encoders have poor accuracy. It’s not unusual for them to have much lower accuracy than their resolution. For example, a 14-bit on-axis sensor may provide transitions every 0.02 degrees, but the error could be 50 times larger than this.
  • Conversely, off-axis magnetic encoders provide much higher accuracy than on-axis magnetic encoders. Timken engineers have patented magnetic encoder designs that use Hall effect technology to obtain high resolution from a durable magnetic target disc.
Timken off-axis magnet encoders are capable of providing more than enough resolution and accuracy for the vast majority of encoder needs.

The Rise of High-Resolution Magnetic Encoders: A Short History

Rotary encoders provide position feedback in all sorts of systems. The demand for encoders continues to grow as customers demand higher efficiency and smarter motion control.

In the beginning
In the old days, encoders were baseball-sized metal cans containing a glass disk with opaque metal lines. Other parts included a set of bearings and a shaft used to mount the glass disk. One side of the disk had an incandescent or LED light source and lens assembly; the other reverse had a metal grating mounted in front of two or three light sensors.  More...