3.24.3 PC-2# Bandwidth Settings
Parameters for setting the bandwidth within which the
pressure is allowed to operate before staging/destaging
fixed speed pumps. Also includes various timers to stabilise
the control.
PC-20 Staging Bandwidth
Range:
Function:
10
%
*
[1 -
par.
PC-21
%]
Set the staging bandwidth (SBW) percentage to
accommodate normal system pressure fluctuation.
In cascade control systems, to avoid frequent
switching of fixed speed pumps, the desired
system pressure is typically kept within a
bandwidth rather than at a constant level.
The SBW is programmed as a percentage of
parameter CL-13 Minimum Reference/Feedb.
parameter CL-14 Maximum Reference/Feedb.
For
example, if the setpoint is 5 bar and the SBW is
set to 10%, a system pressure between 4.5 and 5.5
bar is tolerated. No staging or de-staging occur
within this bandwidth.
Illustration 3.61 Staging Bandwidth
PC-21 Override Bandwidth
Range:
Function:
100
%
*
[par.
PC-20 -
100 %]
When a large and quick change in the system
demand occurs (such as a sudden water
demand), the system pressure rapidly changes
and an immediate staging or destaging of a
fixed speed pump becomes necessary to match
the requirement. The override bandwidth (OBW)
is programmed to override the staging/
destaging timer (
and
parameter PC-24 SBW Destaging Delay
)
for immediate response.
The OBW must always be programmed to a
higher value than the value set in
parameter PC-20 Staging Bandwidth
. The OBW is
a percentage of
and
parameter F-53 Maximum
Reference
.
PC-21 Override Bandwidth
Range:
Function:
Illustration 3.63
Setting the OBW too close to the SBW could
defeat the purpose with frequent staging at
momentary pressure changes. Setting the OBW
too high might lead to unacceptably high or
low pressure in the system while the SBW
timers are running. The value can be optimised
with increased familiarity with the system. See
To avoid unintended staging during the
commissioning phase and fine-tuning of the
controller, initially leave the OBW at the factory
setting of 100% (Off). When the fine-tuning is
completed, set the OBW to the required value.
Initial value of 10% is suggested.
PC-22 Fixed Speed Bandwidth
Range:
Function:
par.
PC-20
%
*
[par.
PC-20 -
par.
PC-21 %]
When the cascade control system runs
normally and the frequency converter issues
a trip alarm, it is important to maintain the
system head. The cascade controller does this
by continuing to stage/destage the fixed
speed pump on and off. As keeping the head
at the setpoint would require frequent
staging and destaging when only a fixed
speed pump is running, a wider fixed speed
bandwidth (FSBW) is used instead of SBW. In
alarm situations, or if the start signal on the
digital input goes low, it is possible to stop
the fixed speed pumps by pressing [Off] or
[Hand].
If the issued alarm is a trip lock alarm, the
cascade controller stops the system
immediately by cutting out all the fixed
speed pumps. This is basically the same as
emergency stop (coast/coast inverse
command) for the cascade controller.
Parameter Description
AF-600 FP
™
Programming Guide
DET-620D
03/2016 All rights reserved.
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