Danfoss VLT Refrigeration Drive FC 103 Programming Manual page 175

Parameter Description
25-22 - Zone [unit]
Range:
25-23 Fixed Speed neutral Zone [unit]
Range:
4 ReferenceFeed- [0 - 9999.99
backUnit ReferenceFeed-
*
backUnit]
MG16H202
Programming Guide
Function:
Do not set the -zone value
too close to 0 to avoid
frequent stagings at
momentary pressure
changes. See
parameter 25-27 -- Zone
Delay.
To avoid unintended
staging during the
commissioning and fine-
tuning of the controller,
start with the -zone value
beyond any expected
pressure drop. This
implicitly disables the
override function for
pressure drops. When the
fine-tuning is complete,
set the -zone value to the
required value. For
example, use 3 ˚C as the
initial value.
Function:
When the pack control
system is running normally
and the frequency
converter issues a trip
alarm, it is important to
maintain the system head.
The pack controller does
this by continuing to stage/
destage fixed speed
compressors on and off.
When only a fixed speed
compressor runs, keeping
the head at the setpoint
requires frequent staging
and destaging. To avoid
frequent staging and
destaging, the frequency
converter uses a wider
fixed speed bandwidth
(FSBW) instead of SBW. If
an alarm occurs, stop the
fixed speed compressors by
pressing [Off], or [Hand
On], or set the signal
programmed for start on a
digital input to low.
If the issued alarm is a trip
lock alarm then the pack
controller stops the system
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25-23 Fixed Speed neutral Zone [unit]
Range:
25-24 + Zone Delay
Range: Function:
120 s [0 - When the pressure in the system exceeds the
*
3000 s] neutral zone value for a moment, immediate
staging of a fixed speed compressor may cause
damage to equipment. The +zone delay delays
the staging of a fixed speed compressor. If the
pressure gets within the neutral zone before
the timer has elapsed, the timer is reset and
no staging occurs.
25-25 - Zone Delay
Range: Function:
60 s [0 - When the pressure in the system drops below
*
3000 s] the neutral zone value for a moment,
immediate destaging of a fixed speed
compressor may cause damage to equipment.
The -zone delay delays the destaging of a fixed
speed compressor. If the pressure gets within
the neutral zone before the timer has elapsed,
the timer is reset and no destaging occurs.
25-26 ++ Zone Delay
Range: Function:
60 [0 - Staging a fixed speed compressor creates a
s 300 s] momentary pressure peak in the system, and the
*
pressure may exceed the sum of the neutral zone
value and the +zone value. If the pressure peak is
short, the frequency converter should not
destage a compressor. The ++zone delay prevents
staging until the system pressure is stabilized and
normal control is established. Set the delay to a
value that allows the system to stabilize after
staging.
Since +zone delay may be too long to react to a
high-pressure peak, the ++zone delay should be
shorter than the +zone delay. The 60 s factory
setting is appropriate in most applications. In
highly dynamic systems, use a shorter time.
Function:
immediately by cutting out
all the fixed speed
compressors. This is the
same as emergency stop
(coast/coast inverse
command) for the pack
controller.
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