Encoder Resolution, Encoder Accuracy and System Repeatability

Encoder feedback is essential to the performance of many automation applications. Properly specified, an encoder will deliver the results needed to support effective positioning at a price that suits the budget. Improperly specified, it can degrade system performance. To understand how and why, we need to discuss the concepts of accuracy, resolution, and repeatability as they apply to encoders.

Encoder resolution is the number of measuring segments or units in one revolution of an encoder shaft or 1 in/mm of a linear scale. Encoder resolution is commonly measured in pulses per revolution (PPR) for incremental encoders and bits for absolute encoders.

Encoder accuracy is a measure of the error between the value read out by the encoder and the actual physical value being measured.

The third key characteristic of encoders is repeatability. Repeatability is a measure of how consistently the system can return to the same commanded position. For encoders, repeatability typically would be 2-10 times better than accuracy. Like accuracy, repeatability has error contributions from multiple sources, which include the encoder and the equipment being positioned.