274 Rockwell Automation Publication MOTION-UM003K-EN-P - January 2019
Chapter 12 Homing
Behavior of APR for Incremental Encoders
APR for incremental encoders means Absolute Machine Reference Position
Retention. When an incremental encoder is homed, the homed bit is set. An
APR fault is generated and the home axis bit clears when any of the events or
conditions that generate an APR fault for an absolute encoder occur.
For example, the behavior of APR faults for an incremental encoder is identical
to that of an absolute encoder. The exception to this behavior is when an
incremental encoder is power cycled and its position comes up as 0. Its
Absolute Machine Reference Position is lost. An APR fault is not generated.
Saving an ACD File Versus Upload of a Project
The following is an example of a sequence of events that can generate an APR
fault.
1. Make an online change to an axis attribute that generates an APR fault.
2. Rehome the axis.
This action is normally done so APR restores axes positions after a
download.
3. Save your project.
4. Download your project.
You still get an APR fault because saving the project only uploads the
tags, not the changed attributes.
IMPORTANT You must upload the project for the changed attributes to be saved
and to help prevent an APR fault on a subsequent download.
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