ABB ACS850-04 series, Firmware Manual

Page: 70 / 296

70 Program features
Process PID control
There is a built-in PID controller in the drive. The controller can be used to control
process variables such as pressure, flow or fluid level.
In process PID control, a process reference (setpoint) is connected to the drive
instead of a speed reference. An actual value (process feedback) is also brought
back to the drive. The process PID control adjusts the drive speed in order to keep
the measured process quantity (actual value) at the desired level (setpoint).
The simplified block diagram below illustrates the process PID control.
For a more detailed block diagram, see page 292 .
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Sleep function for process PID control
The following example visualizes the operation of the sleep function.
The drive controls a pressure boost pump. The water consumption falls at night. As a
consequence, the process PID controller decreases the motor speed. However, due
to natural losses in the pipes and the low efficiency of the centrifugal pump at low
speeds, the motor would never stop rotating. The sleep function detects the slow
rotation and stops the unnecessary pumping after the sleep delay has passed. The
drive shifts into sleep mode, still monitoring the pressure. The pumping resumes
when the pressure falls under the predefined minimum level and the wake-up delay
has passed.
Process
PID
AI1
Process
actual
values
AI2
• • •
D2D
FBA
Setpoint