Advantech PC-LabCard PCI-1784 - Manual (Page 51)

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Appendix D. Operation
D.1 Quadrature encoder introduction
In typical closed-loop control systems, also know as servo system, 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 which 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
BUS
HOST
CPU
PCI-1784
ENCODER
CARD
QUADRATURE
ENCODER
(MOTOR)
QUADRATURE
SIGNAL
PHASE A
PHASE B
INDEX
QUADRATURE
SIGNAL