Cascade Controller Option
Standard Cascade
Controller Setup
Quick Menu 025 Par. 716 Override bandwidth
(OVERRIDE BANDW%)
Value:
2 - 100 % (100 = OFF)
✭
100 = OFF
Function:
When a large and quick change in the system
demand (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 for immediate response. The
override bandwidth is a percentage of the setpoint and
defines the feedback (pressure) at which the timers
(set in parameters 714, 715) are overridden. For
example, if the setpoint is 5 bar and the override is set
to 20%, the low limit is 4 bar and the high limit 6 bar.
Description of choice:
The OBW must always be programmed to a higher
value than the staging bandwidth (SBW) set in
parameter 713. 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 optimized
with increased familiarity with the system. See
parameter 717,
Override Bandwidth Timer
.
Commissioning the Cascade Controller
To avoid unintended staging during the commissioning
phase and fine tuning of the controller, initially leave
the OBW at the factory setting of 100%. When the
fine tuning is completed, the OBW should be set to
the desired value. A good initial value may be 10%.
Quick Menu 026 Par. 717 Override Bandw. timer
(OVERRIDE TIMER)
Value:
0 - 300 sec.
✭
10 sec.
Function:
Staging a fixed speed pump creates a momentary
pressure peak in the system, which might exceed
the override bandwidth (OBW). It is not desirable
to destage a pump in response to a staging
pressure peak. The override bandwidth timer can
be programmed to prevent staging until the system
pressure has stabilized and normal control established.
Description of choice:
Set the timer to a value that allows the system to
stabilize after staging. The 10 second factory setting
is appropriate in most applications. In highly dynamic
systems, a shorter time might be desirable.
Quick Menu 027 Par. 718 Transition frequency
(TRANSITION FREQ %)
Value:
0 - 120 % of F
max
✭
90%
Function:
The adjustable speed pump typically runs at maximum
speed when staging on an additional fixed speed
pump to match the system demand.
MG.60.I3.02 - VLT is a registered Danfoss trademark
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