Fixed Speed Bandwidth; Sbw Staging Delay - Danfoss VLT Programming Manual

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VLT HVAC Drive Programming Guide

25-22 Fixed Speed Bandwidth

Range:
Application [Application dependant]
dependent*

25-23 SBW Staging Delay

Range:
15 s* [0 - 3000 s]
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 par. 25-25 OBW Time
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, the
OBW should be set to the desired value. An initial value of 10% is suggested.
Function:
When the cascade control system is running 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. Due to the fact that 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. It is possible to stop the fixed speed
pumps, in case of an alarm situation, by pressing the LCP OFF or HAND ON keys or if the signal
programmed for Start on digital input goes low.
In case the issued alarm is a trip-lock alarm then the Cascade Controller must stop 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.
Function:
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 program-
med. If the pressure increases to within the SBW before the timer has elapsed, the timer is reset.
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