2-140 Process PI Loop
regardless of flow changes. With the drive turning the pump at the required
speed, the pressure is maintained in the system.
However, when additional valves in the system are opened and the pressure
in the system drops, the PI error will alter its output frequency to bring the
process back into control.
When the PI is disabled the commanded speed is the ramped speed
reference.
When the PI is enabled, the speed reference is disconnected and PI 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
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