Rockwell Automation 20A PowerFlex 70EC/700VC - Manual (Page 83)

Process PID Loop 79
However, when additional valves in the system are opened and the pressure in the
system drops, the PID error will alter its output frequency to bring the process back
into control. When the PID is disabled the commanded speed is the ramped speed
reference.
When the PID is enabled, the speed reference is disconnected and PID Output has
exclusive control of the commanded speed, passing through the linear ramp and
s-curve.
PI Feedback
Motor
Pump
Desired Pressure
[PI Reference Sel]
Pressure
Transducer
Spd Cmd
Process PI
Controller
Linear Ramp
& S-Curve
+
+
PI Disabled Speed Control
Spd Ref
PI Ref
PI Fbk
Slip Adder
Open
Loop
Slip
Comp
Process
PI
Spd Cmd
Process PI
Controller
Linear Ramp
& S-Curve
+
+
PI Enabled Speed Control
Spd Ref
PI Ref
PI Fbk
Slip Adder
Open
Loop
Slip
Comp
Process
PI