Rockwell Automation 4100 AEC Absolute Encoder Converter Installation - Manual (Page 43)

35 Publication 4100-UM052B-EN-P - October 2001
Chapter
4
Operation
Chapter Objectives This chapter provides an overview of how the AEC determines
position. This chapter covers the following topics:
•
Absolute Position Update
•
Incremental Position Output
•
Position at Start-up
Absolute Position Update Absolute position information can be requested from the transducer
via the AEC at any time. When the AEC interprets the strobe pulse
train to be an absolute update request from the controlling hardware,
it interrogates the transducer’s absolute position and incrementally
streams the position to the awaiting controller.
Incremental Position
Output The AEC checks for the transducer position periodically. In the
Locked mode of operation, this process is triggered and synchronized
by the strobe input. In the Free-running mode of operation, the
position is sampled, calculated, and transmitted every 1/1000
th
of a
second, based on the internal time of the AEC. The AEC compares the
newly sampled absolute position against the last. It calculates the
difference between the new and the old positions and transmits the
difference through the encoder port in an incremental fashion.
The position and direction information is encoded and sent using the
industry standard (A and B) channels in quadrature (90 degree
phasing). Each channel is driven differentially for improved noise
immunity. When moving in the positive direction, the phase of the
quadrature pulse train is A leading B. When moving in the negative
direction, the phase of the quadrature pulse train is B leading A. The
output frequency of both channels is fixed at 800kHz. One transducer
position count is represented by one edge transition (either positive or
negative) of the quadrature pulse train. This encoding scheme is
defined as 4X. Your position controller must support the 4X decode of
the AEC encoder output.
IMPORTANT
During an absolute position update, the quadrature
encoder output stream is always positive: A leads B. See
the Incremental Position Output section of this manual
for more details.