Emerson FM-3 - Manual (Page 49)

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Setting Up Parameters
Motor Position Group
Position Command
Position command is the commanded motor position sent to the drive by the FM-3 module.
This parameter does not take following error into account. See also PosnFeedback and
FollowingError. Units are in user units.
Position Feedback
Feedback position is the actual motor position in user units. PosnCommand minus the
PosnFeedback is the FollowingError
Following Error
The Following Error is the difference between the Position Command and the Position
Feedback. It is positive when the Position Command is greater than the Position Feedback.
Encoder Position
Motor encoder position in encoder counts. This position reflects the feedback position of the
motor and is not scaled into user units. This is a signed 32 bit value.
Motor Velocity Group
Velocity Command
The Velocity Command is the velocity that the FM-3 module is commanding the motor to run
at. This command is generated by the drive velocity control loop and position loop. It is
displayed in user units.
Velocity Feedback
This is the feedback (or actual) velocity. It is calculated using the change in position of the
motor encoder. It will always return the actual motor velocity - even in synchronized
applications in which the master axis is halted during a move.
Control Loop Group
Changing the Trajectory Update Rate can have a major effect on the performance of your
servo system. A longer trajectory update rate means that more time is available to process user
programs. A shorter update rate means that the control loop is updated more often and
provides the most accurate performance. Without proper diagnostics, it can be impossible to
tell how much time is being consumed by the control loop update, and how much time is
available to run user programs.
The Control Loop group of parameters on the Status Online tab shows the user how much
time is available to run programs. There are two parameters available to help with this. They
are as follows: