Glossary · Motion control and drives
Quadrature signals
Also known as: A/B signals, Quadrature encoder signals
German: A/B-Spursignale
In motion control, quadrature signals are the two square-wave signals A and B of an incremental encoder, phase-shifted by 90 electrical degrees, from which the controller derives position by counting edges and the direction of motion from which signal leads.
- Motion control
In one sentence
Quadrature signals are an incremental encoder's A and B tracks, 90° apart; counting edges gives position, the leading track gives direction.
Example
An encoder with 1,000 lines per revolution delivers 4,000 counts per revolution to the drive, because the drive counts all four edges of the A and B signals.
How it applies
- Engineering: Signals are output as TTL/RS-422 differential lines (A, /A, B, /B) or as HTL single-ended signals. Differential lines tolerate longer cables and more interference.
- Commissioning: Swapping A and B inverts the counting direction. Check the direction and the count per revolution before closing the position loop.
- Operation: Noise can add or drop counts; the position then drifts until the next homing.
- Documentation: Distinguish lines (pulses) per revolution from counts per revolution after quadruple evaluation; mixing them up gives a factor-of-four error in scaling. Name the signal standard and the pin assignment.