Control macros 125
Pump and Fan Control (PFC) macro
The PFC macro is suitable for pump or fan systems consisting of one drive and
multiple pumps/fans.
The PFC macro can be used to:
• Control the speed of one of the pumps/fans
• Connect or disconnect the auxiliary pumps in Direct On Line (DOL) connection as
and when required.
For example, in a pump application with multiple pumps, the PFC logic controls the
pumps as follows:
1. The drive varies the motor speed (VSD motor) to control the output of the first
pump. This pump is the speed regulated pump.
2. When the demand (represented by the process PID reference) exceeds the
capacity of the first pump (a user defined speed/frequency limit), the PFC logic
automatically starts the auxiliary pump using the drive relay output.
3. The PFC logic reduces the speed of the first pump to balance the system output
and to get the optimum energy efficiency.
4. The PID controller adjusts the speed/frequency of the first pump in such a way
that the system output meets the process need.
5. If the demand further increases, the PFC logic adds further auxiliary pumps in
similar manner.
6. When the demand drops, the drive reduces the speed of the first pump and when
it reaches below the minimum limit (user defined speed/frequency limit), the PFC
logic automatically stops the auxiliary pump. At the same time, the PFC logic
increases the speed of the first pump to account for the missing output of the
stopped auxiliary pump.
Note: The PFC is supported in external control location EXT2 only. However, you can
use EXT1 for manual control of pump 1.
The below timing diagram explains how and when an auxiliary pump is connected
with the PFC logic.
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