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Confi guration 4: a pRack pR300T board for managing the two suction
lines and a board for control of the high pressure part:
pLAN 1
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Fig. 6.e
6.2 Unit On-Off
The unit can be switched on and off from:
•
User terminal
•
Supervisor
•
Digital input
On-off from the user terminal and the confi guration parameters are
available under the main menu, branch A.c, and are diff erentiated based
on the access level; the User password allows display only.
On-off from the supervisor and from the digital input and start-up after
a blackout (with specifi c delay, to avoid continuous starts and stops in
the event of instability in the power supply) must be enabled using the
parameters visible only with the Manufacturer password.
On-off from the digital input is equivalent to an enabling Signal, that is, if
the digital input is Off the unit cannot be switched on in any other way,
while if is On, the unit can be switched on or off in any other way, with
the same priority (the most recent control has precedence, whatever the
origin), as shown in the fi gure:
Digital Input
User interface
Supervisor
Unit On/Off
When there are two suction and condenser lines, on-off is independent for
each line, while when there are two suction lines and one condenser line,
it is independent for the suction lines, while the condenser line stops when
both suction lines are off , and starts when at least one suction line is ON.
Copyright HPL March 2021
pLAN 3
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Fig. 6.f
Note: certain special conditions or functions in the pRack software
cause the unit to shutdown:
•
Confi guration of some parameters: e.g. inputs/outputs, confi guration
of compressors, inverter parameters.
•
Installation of default parameters
•
Manual management
6.3 Control
pRack PR300T can manage two types of control:
•
Proportional band (P, P+I);
•
Neutral zone (fi xed times, variable times).
Both types of control can be applied to both compressors and
condensers, according to the settings defi ned during start-up or in main
menu branches C.a.b/C.b.b and D.a.b/D.b.b.
The type of control chosen is independent for each line present, either
suction or condenser. In addition, pRack PR300T can use as the reference
for control either the pressure or the converted temperature, or the
temperature read by probe if there is no pressure probe, even if reference
is only made to pressure below.
The control set point can be compensated by an off set linked to digital
inputs, probes, supervisor or time bands, for details see paragraph 6.5
relating to compressor and fan energy saving. Both types of control are
described below, and are valid for both control of suction pressure and
condensing pressure, and operation with backup probes and/or probes
not working.
6.3.1
Proportional band
The operating principle is normal proportional or proportional + integral
control (P, P+I).
The control set point is central, consequently - for proportional control
only - operation is schematised in the following fi gure:
100%
Differential
Setpoint
For example, for 4 devices with the same capacity and proportional only
control, start-up occurs as shown in the fi gure:
C1
C2
Differential
Setpoint
33
Page 82 of 169
Regulation request
Regulation
Differential
probe value
Fig. 6.g
Devices activation
C3
C4
Suction
Differential
pressure
Fig. 6.h
P4367 Rev 01
pRack PR300T +0300018EN rel. 1.5 - 02.05.2017
ENG
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