by Jason Kelly, CUI
Incremental rotary encoders produce two square wave outputs as they rotate, from which the angular displacement and rotational speed can be calculated. These quadrature outputs let the host system determine the direction of rotation.
To calculate speed and angular displacement, the encoder’s resolution – equivalent to the angular displacement represented by a single pulse – must be known. Although the resolution is stated in the datasheet, different manufacturers use various terms and acronyms.
Pulses Per Revolution (PPR), Counts Per Revolution (CPR), and Lines Per Revolution (LPR) are common, but Periods Per Revolution or Cycles Per Revolution are sometimes used. This introduces opportunities for error: a 2-bit quadrature output produces four counts in each cycle, so while one revolution usually contains the same number of pulses, periods or cycles, confusing cycles and counts can put calculations out by a factor of four.
In the CUI Insights blog post, “What’s the Difference Between and Incremental Encoder’s PPR, CPR, and LPR?”, they explain the principles behind incremental encoders and define the various ways resolution is measured to help avoid such errors.