Version 2.02 15.05.2007 Function of VS 3000
14
3.7 Processing load-level information
Each case/coldroom controller on which load-level transmission is activated transmits up to four load levels to
the respectively assigned pack controller at intervals.
Decrease of low-pressure setpoint takes place on the pack controller when a single load level exceeds the de-
finable maximum load level. Increase of low-pressure setpoint takes place on the pack controller when the load
level of all case/coldroom controllers falls below the definable minimum load level. For this purpose an averaged
load level (arithmetical mean of up to four separate load levels for each case/coldroom controller) is computed
and saved by the VS 3000 for each case/coldroom controller (maximum 99 total).
If one of the four load levels of a refrigeration point is greater than the maximum load level, the mean load level
is ignored for temperature shift. N o suction pressure increase then takes place although the mean low level of
all refrigeration points is below the minimum load level.
When neither of the above conditions applies, the t
0
setpoint remains at the given value. No suction pressure
increase takes place as long as superheat control is active on at least one refrigeration point.
Only when superheat control is not active on any of the associated refrigeration points can low pressure be in-
creased according to the above rules. The reason for this is that, during superheat control, the valve opening at
the refrigeration point is normally small while refrigeration load continues high. In other words, this is a precau-
tion against erroneously increasing low pressure.
Change of low-pressure setpoint takes place within definable limits at definable increments and a definable up-
dating interval.
3.8 Response to fault conditions
Can bus fault on individual stations:
If no telegram is received from a given case/coldroom controller during a time longer than the timeout period for
load level reception, the mean load level for the controller concerned will be ignored until such time as a new
telegram is received.
Global bus fault:
The current t
0
setpoint is retained. At the end of a 10-minute alarm delay, a No Load Level fault is logged and is
not reset until new load level information is received via the CAN bus.
3.9 Demand-dependent setpoint shift parameters
The range within which t
0
can be changed is defined by the parameters t
0
-max and t
0
-min (Menu 3-2-3).
Change to the second setpoint does not take place with demand-dependent setpoint shift.
The Max.LoadLevel parameter (Menu 3-2-2) defines the maximum load level (valve opening) for decrease of
the t
0
setpoint.
The Min.LoadLevel parameter (Menu 3-2-2) defines the minimum load level (valve opening) for increase of the
t
0
setpoint.
The Increment parameter (Menu 3-2-2) defines the increment in Kelvin by which the t
0
setpoint is increased or
decreased after a definable time interval expires.
The Interval parameter (Menu 3-2-2) defines the interval in minutes that must expire before the t
0
setpoint is up-
dated as required.
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