Rockwell Automation 1395 Digital DC Drive FRN 5-10.10/9.30 - Manual (Page 114)

Chapter 5
Functional Description
5-28
Torque Select (Circle 8)
Selects the reference input to the Current Control, based on the value of
Torque Mode (Parameter 625). Torque Mode is a number coded parameter
which allows operation under several different torque modes.
There are two possible reference inputs to choose from. The output of the
Velocity PI Control, which has been converted to a torque reference, is
used as an internal torque reference. If the drive is a stand alone drive, or
considered the Master drive of a system, this reference could be used. The
external Torque Reference, (Parameter 157), is used to supply an external
torque reference for the drive. This could be used if the drive was a slave
drive in a system. This parameter can also be modified by summing the
Process Trim Output when the Process Trim Select (Parameter 628) selects
the torque reference to trim. The external torque reference is also used
when either the “Min” or “Max” torque modes are selected. These
functions automatically make a selection between the external torque
reference value and the output of the Velocity PI Control.
Torque Command, (Parameter 110), indicates the latest torque reference
value. This value is converted to an armature current reference by dividing
by the motor Field Flux Command, to be used in the Current PI Control.
The value is also used as an input to the Droop Control.
Feedback Control (Circle 14)
Two current transformers (CT’s) sense armature current flow. The current
feedback is scaled using Motor Armature Full Load Amps (Parameter 611)
and Rated Armature Bridge Current (Parameter 615). Parameter 112 is the
average armature current feedback value. The field current transducer
(FCT) provides field current feedback to the control which is scaled by
Rated Field Motor Current (Parameter 612) and Rated Field Bridge Current
(Parameter 616). The average field current can be read by Parameter 118.
Tach Loss Recovery
When Tach Loss Recovery is selected, it allows the Drive to continue
operation under armature voltage control in the event that the primary
feedback device fails (the primary device can be an encoder or DC tach).
The switchover occurs automatically and does not shut the Drive down.
This feature also provides an option for configuring a tach loss as a
Warning Fault. This is done with Parameter 691 “Tach Switch Sel”. If
Parameter 691 is set to one, the Tach Loss Recovery feature is activated
and Tach Loss becomes a Warning fault. If Parameter 691 is set to zero, a
tach loss causes a soft fault. The default value for Parameter 691 is zero
(tach loss recovery disabled).