90 Rockwell Automation Publication 843ES-UM001A-EN-P - February 2020
Appendix D Use of Controller-based Safety Functions with the 843ES CIP Safety Encoder
SFX Instruction Example
The SFX instruction scales the applicable safety instructions with feedback
position units from the safety encoder, into position feedback units used in
applicable safety instructions. It also scales feedback velocity units from the safety
encoder into position feedback units per time unit.
Scaling Setup
When configuring the SFX instruction, calculate the value for Position Scaling so
that the Actual Position and Actual Speed output from the instruction matches
the Actual Position and Actual Velocity in the motion controller.
Values from Encoder Safety Configuration are required to calculate the
instruction input.
The SFX Feedback Resolution is determined based on the feedback device and
the Resolution of the feedback. This information is configured on the Encoder
Safety Configuration page.
Figure 17 - Effective Resolution Parameter
In Figure 17, the encoder is monitoring for a rotary application where the
unwind is set to rollover each motor revolution. Therefore, the unwind of 512
counts/revolution was added in the SFX instruction appropriately.
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