25-21 Override Bandwidth
Range:
Function:
completed, set the OBW to the required value.
Initial value of 10% is suggested.
25-22 Fixed Speed Bandwidth
Range:
Function:
Size
related
*
[ par.
25-20 -
par.
25-21 %
]
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 On].
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.
25-23 SBW Staging Delay
Range:
Function:
15
s
*
[0 -
3000
s]
Immediate staging of a fixed speed pump is not
desirable when a momentary pressure drop in the
system exceeds the staging bandwidth (SBW).
Staging is delayed by the length of time
programmed. If the pressure increases within the
SBW before the timer has elapsed, the timer is
reset.
Illustration 3.84 SBW Staging Delay
25-24 SBW Destaging Delay
Range:
Function:
15
s
*
[0 -
3000
s]
Immediate destaging of a fixed speed pump is not
recommended when a momentary pressure
increases in the system that exceeds the staging
bandwidth (SBW). Destaging is delayed by the
length of time programmed. If the pressure
decreases within the SBW before the timer has
elapsed, the timer is reset.
175ZA671.11
(27-24) SBW destage delay
SBW
SBW
Setpoint
(27-20)
(27-20)
Illustration 3.85 SBW Destaging Delay
25-25 OBW Time
Range:
Function:
10
s
*
[0 -
300 s]
Staging a fixed speed pump creates a momentary
pressure peak in the system, which might exceed
the override bandwidth (OBW). It is not
recommended to destage a pump in response to a
staging pressure peak. The OBW time can be
programmed to prevent staging until the system
pressure has stabilized and normal control
established. Set the timer to a value that allows the
system to stabilize after staging. The 10 s factory
setting is appropriate in most applications. In highly
dynamic systems, a shorter time may be wanted.
Setpoint
SBW (27-70)
OBW (27-71)
SBW (27-70)
OBW (27-71)
Actual head
OBW timer (27-25)
130BA370.11
Illustration 3.86 OBW Time
Parameter Description
VLT
®
AQUA Drive FC 202
210
Danfoss A/S © 05/2018 All rights reserved.
MG20OB02
3
3
Summary of Contents for VLT AQUA Drive FC 202
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