Rockwell Automation Liqui-Flo DBT Reach Drive User Manual
Page 57
Parameter Descriptions
3-31
PI control allows the drive to take a reference signal (setpoint) and an actual signal
(feedback) and automatically adjust the speed of the drive to match the actual signal
to the reference.
Proportional control (P) adjusts the output based on the size of the error (larger error =
proportionally larger correction).
Integral control (I) adjusts the output based on the duration of the error. The integral
control by itself is a ramp output correction. This type of control gives a smoothing
effect to the output and will continue to integrate until zero error is achieved.
By itself, integral control is slower than many applications require, and, therefore, is
combined with proportional control (PI).
The purpose of the PI regulator is to regulate a process variable such as position,
pressure, temperature, or flow rate, by controlling speed.
There are two ways the PI regulator can be configured to operate (see parameter
124):
•
Process trim, which takes the output of the PI regulator and sums it with a master
speed reference to control the process.
•
Process control, which takes the output of the PI regulator as the speed command.
No master speed reference exists, and the PI output directly controls the drive
output.
Note that Feedback Select (80) must be set to Process PI (2).
Bit 0 - PI Enable
•
Enables/disables the operation of the PI loop.
Note: To use the PI loop, Bit 0 must be set to Enable (1), even if a digital input has
been programmed to be used as a PI Enable (See parameters 361-366).
Bit 1 - PI Hold
•
Enabled = The integrator for the outer control loop is held at the current level; that
is, it will not increase.
•
Disabled = The integrator for the outer PI control loop is allowed to increase.
Bit 2 - PI Reset
•
Enabled = The integrator for the outer PI control loop is reset to zero.
•
Disabled = The integrator for the outer PI control loop integrates normally.
Figure 3.6 – PI Control (125)
0
0
x
0
x
x
x
x
x
x
x
x
x
x
x
x
10
0
1
2
3
4
5
6
7
8
9
11
12
13
14
15
1 =Enabled
0 =Disabled
x =Reserved
Bit #
Factory Default Bit Values
PI Enable
PI Hold
PI Reset
Nibble 1
Nibble 2
Nibble 3
Nibble 4