The controller's integral term (integration over time) ensures steady-state accuracy in
controlled systems with compensation function. Once the controlled variable has
reached its steady-state value, the offset will be zero, provided parameterisation is
correct. Depending on its value, the integral term of the controller PI Integral Tm
(3-9-1-3)
has the following effect on the control characteristics:
▪
Low value selected for PI Integral Tm
(3-9-1-3)
: Faster elimination of offset, if any.
This may, however, cause the value of the controlled variable to oscillate around
the setpoint and result in control process instability.
▪
Large value selected for PI Integral Tm
(3-9-1-3)
: Considerably reduces the
controller's response speed
Actual value
Setpoint
3--9--1--2
Value too large
3--9--1--2
Value optimal
3--9--1--2
Value too small
Time
Point in time at which a sudden
change in setpoint occurs (dashed line)
Fig. 35: Setting the proportional gain
Actual value
Setpoint
3--9--1--3
Value too large
3--9--1--3
Value optimal
3--9--1--3
Value too small
Time
Point in time at which a sudden
change in setpoint occurs (dashed line)
Fig. 36: Setting the integral term
7.1.1.4.1 Closed-loop control mode via control panel
The setpoint can be specified using the control panel. For this purpose, the Setpoint
Source 2 parameter
(3-5-4-2)
must be set to Configurable Setpoint (factory setting).
The setpoint unit is set using the Setpoint Unit parameter
(3-2-2-1)
. Depending on
the unit selected, the setpoint is specified using the Configurable Setpoint parameter
(3-5-2-1)
. The Max Setpoint parameter
(3-5-1-3)
Section 7.1.1.2 Page 49) must be
set identically to parameter
(3-8-2-8)
Analog IN 1 High or
(3-8-3-8)
Analog IN 2 High,
depending on the feedback source selected.
PumpDrive is to control the system to achieve a setpoint of 6.7 bar in a differential
pressure control process. For this purpose, a differential pressure sensor (4 - 20 mA)
with a measuring range of 0 to 10 bar is connected to analog input 2 of PumpDrive.
The setpoint is specified using the control panel.
Example
7 Commissioning/shutdown
PumpDrive
59 of 162
