ABB DriveIT ACH550-01 User Manual page 272

PID Controller - Advanced
ACH550 has 2 separate PID Controllers:
1. Process PID (PID1) and
2. External PID (PID2)
Process PID (PID1) has 2 separate sets of parameters:
a) Process PID (PID1) SET1, defined in Group 40 and
b) Process PID (PID1) SET2, defined in Group 41
The user can select between the 2 different sets by using
parameter 4027
Typically two different PID-Controller sets are being used when
the load of the motor changes considerably from one situation to
another.
External PID (PID2) - defined in Group 42 - can be used in 2
different ways:
a) Instead of using additional PID-controller Hardware, it can be
set to control a field instrument like a damper or a valve via
outputs of the ACH550. In this case Parameter 4230 to be set to
value 0. (0 is the default value.)
b) External PID (PID2) can be used as an additional PID-
controller to Process PID (PID1) to trim or fine-tune the speed of
ACH550.
An example of the trimming is a return fan that follows the speed
of the supply fan. As the return fan needs to run faster or slower
then the supply fan in order to create under- or overpressure,
correction factors to the supply fan speed are needed. External
PID (PID2) be used in the return fan ACH550 to provide these
corrections.
268
ACH550 User's Manual
Parameter listing and descriptions