Rockwell Automation 20D PowerFlex 700S with Phase I Control Reference Manual - Manual (Page 148)

148 Rockwell Automation Publication PFLEX-RM002D-EN-E - August 2013
Chapter 1 Detail Drive Configuration and Operation
Motor Speed Feedback and Scaled Speed Feedback
The motor speed feedback is selected according to the feedback device selection.
The value for motor speed feedback appears in parameter
300 [Motor Spd Fdbk]. [Motor Spd Fdbk] is in RPM. From there, the speed
feedback enters the speed regulation loop. The filter for the speed feedback is
shown in the speed regulation loop section.
Branching off of the motor speed feedback, there is a low pass filter. This low pass
filter filters out high frequency before displaying the speed feedback on the HIM.
Parameter 72 [Scaled Spd Fdbk] provides a user scalable speed feedback. It is
multiplied by the value in parameter 73 [Spd Fdbk Scale].
Speed Feedback Loss Ride Through
The speed feedback loss ride through function provides an automatic switch over
from the primary motor speed feedback device to the alternate motor speed
feedback device when a primary motor speed feedback device fault is sensed. If
the alternate speed feedback device has failed the switching will not be allowed
and the drive will fault. The active device can be monitored and manual
switching between the primary and alternate devices is available. This function
has also been referred to as tach loss switch over and encoder loss ride through.
The drive determines that the encoder has faulted based on a combination of
hardware detection and monitoring the rate of change of the motor speed. The
hardware fault detection is based on illegal encoder states and improper encoder
switching patterns. The rate of change of motor speed detection is determined by
a rate of change greater than a user-defined speed change.
Hardware detection of feedback loss for the feedback option cards is based on the
type of device used and specific fault detection implemented on the feedback
option card. The rate of change of motor speed detection is the same
implementation as for encoder feedback.
LPass
Filter
X
300
73
72
Motor Spd Fdbk
Spd Fdbk Scale
Scaled Spd Fdbk
to Speed
Control [3A4]
To HIM Display