Rockwell Automation Liqui-Flo DBT Reach Drive - Manual (Page 221)

Application Notes Appendix D-7
Process PI for Standard Control
The internal PI function of the Reach Drive provides closed loop process control with
proportional and integral control action. The function is designed for use in
applications that require simple control of a process without external control devices.
The PI function allows the microprocessor of the drive to follow a single process
control loop.
The PI function reads a process variable input to the drive and compares it to a
desired setpoint stored in the drive. The algorithm will then adjust the output of the PI
regulator, changing drive output frequency to try and make the process variable equal
the setpoint.
It can operate as trim mode by summing the PI loop output with a master speed
reference.
Or, it can operate as control mode by supplying the entire speed reference. This
method is identified as “exclusive mode.”
Figure D.8 – Trim Mode
Figure D.9 – Control Mode
+
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
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