Rockwell Automation 20D PowerFlex 700S with Phase I Control Reference Manual - Manual (Page 149)

Rockwell Automation Publication PFLEX-RM002D-EN-E - August 2013 149
Detail Drive Configuration and Operation Chapter 1
Speed feedback loss ride through is not allowed in position mode. If the encoder
loss ride through function was allowed in a positioning system it is likely that the
alternate feedback device will supply an arbitrary position feedback value when
an encoder loss is detected. This, in turn, could result in unintended motion in
the drive system.
Speed Feedback Loss Ride Through Configuration
Parameter 151 [Logic Command] bit 2, “TackLoss Rst” provides a manual
switch between primary and alternate speed feedback devices with a “0” to “1” bit
transition. A transition from “1” to “0” does not cause a change in operation.
Parameter 152 [Applied LogicCmd] bit 2, “TachLoss Rst” shows the status of
parameter 151 [Logic Command] bit 2 “TachLoss Rst” switch.
Setting parameter 153 [Control Options], bit 16 “Auto Tach Sw” to a value of “1”
enables the automatic switching of speed feedback devices when a failure is
detected. A value of “0” disables the automatic switching of speed feedback
devices. Only automatic switching from the primary device specified in
parameter 222 [Mtr Fdbk Sel Pri] to the alternate device specific in parameter
223 [Mtr Fdbk Sel Alt] is available. Switching from the alternate to the primary
device must be done manually by setting parameter 151 [Logic Command], bit 2
“TackLoss Rst” from “0” to “1”.
Parameter 155 [Logic Status] bit 12, “Tach Loss Sw,” shows which speed
feedback device is currently active. A value of “0” in bit 12 indicates that the
primary speed feedback device selected in [Mtr Fdbk Sel Pri] is active. A value of
“1” in bit 12 indicates that the alternate speed feedback device selected in [Mtr
Fdbk Sel Alt] is active.
Parameter 222 [Mtr Fdbk Sel Pri] selects the primary speed feedback device. It is
not intended to use the sensorless selection as the primary (or active) speed
feedback device as there is no feedback loss detection used with sensorless
operation.
Parameter 223 [Mtr Fdbk Sel Alt] selects the alternate speed feedback device.
Any selection of feedback devices, including sensorless operation is available
providing a corresponding motor type and associated feedback device is present.
IMPORTANT Even though the encoder loss ride through function attempts to automatically
switch feedback devices with minimum disturbance, a system disturbance will
occur. In some cases feedback device degradation may occur before complete
failure takes place. The user must determine if the encoder loss ride through
function is appropriate for each application.