Appendix D Operation; Quadrature Encoder Introduction - Advantech PCI-1784U User Manual

Appendix D Operation

D.1 Quadrature Encoder Introduction
In typical closed-loop control systems, also know as servo systems, the
encoder interface senses motor position and sends a position signal to the
controller. The diagram below shows a typical servo system.
The encoder generates pulses that indicate the shaft position. The encoder
output includes two signals, commonly called channel A and channel B,
which generate N pulses revolution. The two signals are shifted by a
quarter of a cycle, as shown below. The shift between the two signals
enables the controller to determine the direction of rotation, depending on
whether channel A leads channel B or vice versa.
MICROCOMPUTER
Single-ended vs. differential input
Most encoders produce square wave signals with TTL levels. Industrial
systems often use encoders with differential signals, i.e. channel A and B
and their complements. Differential signals can reduce sensitivity to noise
and allow longer transmission distances. Encoders may also produce a
third signal once per revolution know as the index or marker. The encoder
interface can use the index signal to reset the counter, allowing you to
monitor the position within the current revolution.
PCI-1784U User Manual
BUS
HOST
CPU
PCI-1784
ENCODER
CARD
QUADRATURE
PHASE A
PHASE B
INDEX
QUADRATURE
SIGNAL
52
SIGNAL
QUADRATURE
ENCODER
(MOTOR)