Rockwell Automation MD65 User Manual Version 2.0 - Manual (Page 169)

PID Set Up I-1
A
PPENDIX
I
PID Set Up
PID Loop
The MD65 has a built-in PID (proportional, integral, differential)
control loop. The PID loop is used to maintain a process feedback
(such as pressure, flow or tension) at a desired set point. The PID
loop works by subtracting the PID feedback from a reference and
generating an error value. The PID loop reacts to the error, based
on the PID Gains, and outputs a frequency to try to reduce the error
value to 0. To enable the PID loop, PID Ref Sel (A132) must be set
to an option other than 0 “PID Disabled”.
Exclusive Control
In Exclusive Control, the Speed Reference becomes 0, and the PID
Output becomes the entire Freq Command. Exclusive Control is
used when PID Ref Sel (A132) is set to option 1, 2, 3 or 4. This
configuration does not require a master reference, only a desired
set point, such as a flow rate for a pump.
Example
• In a pumping application, the PID Reference equals the
Desired System Pressure set point.
• The Pressure Transducer signal provides PID Feedback to the
drive. Fluctuations in actual system pressure, due to changes
in flow, result in a PID Error value.
• The drive output frequency increases or decreases to vary
motor shaft speed to correct for the PID Error value.
• The Desired System Pressure set point is maintained as values
in the system are opened and closed causing changes in flow.
–
+
PID Prop Gain
PID Loop
PID Integ Time
PID Diff Rate
PID Enabled
PID Fdbk
PID Ref
PID
Error
+
+
+
PID
Output
Accel/Decel
Ramp
Freq
Command