An encoder measures movement or position.

A rotary encoder converts shaft rotation into electrical information. Optical and magnetic designs are common; their operating principles and interfaces differ.

The receiving system interprets the signal. An encoder attached to a motor measures at that shaft, not directly at every part of the lift.

Incremental encoders report changes.

As the shaft rotates, a repeating pattern passes the sensing elements. Their changing signals let the receiving controller count movement and distinguish its direction.

1. A leads B

Quadrature signals: A leads BA leads B. AB states are 00, 10, 11, 01, 00; edges are A rising, B rising, A falling, B falling. At constant speed, corresponding A and B edges are separated by a quarter of one waveform cycle.AB0010110100AB statesTime →¼ cycleA↑B↑A↓B↓↑ rising edge · ↓ falling edge

Count in one direction: +1 at each transition in this example.

2. B leads A

Quadrature signals: B leads AB leads A. AB states are 00, 01, 11, 10, 00; edges are B rising, A rising, B falling, A falling. At constant speed, corresponding A and B edges are separated by a quarter of one waveform cycle.AB0001111000AB statesTime →¼ cycleB↑A↑B↓A↓↑ rising edge · ↓ falling edge

Reverse the motion: −1 at each transition using the same convention.

  1. Two channels identify direction. Each waveform switches between logic 0 and 1. Compare which channel changes first: reversing movement reverses the state sequence.
  2. Quadrature means a quarter-cycle offset. The signals are 90 electrical degrees apart. That is a quarter of one signal cycle, not necessarily a quarter of a shaft revolution.
  3. ×4 decoding counts all four transitions. A rising, B rising, A falling and B falling each count. One full A cycle therefore produces four counts with this mode; ×1 and ×2 use fewer edges.
Ideal digital signals at constant speed. The positive direction is a convention set by channel order and the receiving system; “A leads” does not universally mean clockwise. The Z/index pulse, when present, is a separate reference signal and is omitted here.

Be clear about the counting convention.

1,024 cycles per revolution

If a receiver counts all four edges of quadrature channels A and B, it records 4,096 counts per revolution. Other counting modes give different totals.

Pulse, cycle and count are not always used consistently between specifications. Resolution describes distinguishable increments; it is not the same as accuracy.

Absolute encoders identify a position.

An absolute encoder provides a position value within its measuring range. Single-turn devices identify angle within one revolution; multi-turn arrangements also distinguish revolutions within their range.

Having an absolute motor angle does not automatically identify the lift’s floor. The system still needs the relationship between that measurement and the installation.

Feedback must represent the intended motion.

Mounting, coupling, signal quality and compatible interfaces matter. An encoder can report its own movement correctly while a loose mechanical connection prevents it from representing the intended shaft.

Position changes over time give speed information. The next lessons show how a drive uses that information to influence motion.

A closer look

An incremental system generally needs a reference or retained position information to know an absolute location. An index pulse can mark a point in each revolution but does not by itself identify which revolution the machine is on.

Check your understanding

Does a higher encoder resolution automatically mean equally high positioning accuracy?

Reveal the explanation

No. Resolution is the size of distinguishable increments. Accuracy also depends on the sensor, mounting, mechanics and interpretation.

Further reading.

Optional reading to explore this lesson in more detail.