Interaction With Ploads; Unit Of Measure; Sign Of Life; Liquid Non-Return - Carel PRK300L3FK User Manual

Note: if it is not possible to have the information on the change in
unit cooling capacity, this will be always be considered as operating at
100% and therefore the procedure will never be used. In this case, the PID
control needs to be more reactive (see Control), so as to respond promptly
to variations in load that are not communicated to the driver.
ON
A
OFF
ON
C
OFF
ON
NP
OFF
ON
R
OFF
T3
Fig. 6.au
Legenda:
A Control request
C Change in capacity
NP Re-positioning
R Control
6.6.8

Unit of measure

pRack pR300 can manage two units of measure, the international system
and Imperial.
Note: the temperature and pressure units of measure can be
changed from °C, barg to °F, psig only during start-up; mixed
confi gurations are not allowed, for example °F and barg.
6.6.9

Sign of life

pRack pR300 can manage a digital output acting as a sign of life, activated
when pRack pR300 is powered up.
This output remains active while the controller is working correctly and
highlights any hardware faults.
The Signal can be confi gured in main menu branch B.a.c.

6.6.10 Liquid non-return

pRack pR300 can manage a digital output with the meaning of liquid
non-return. This normally active output is deactivated when all the
compressors are off and no compressor can be started due to alarms or
time settings, despite the control request, or when the unit is OFF. As soon
as at least one compressor is enabled to start, the output is deactivated,
allowing management of a liquid non-return valve. The function can be
confi gured in main menu branch C.a.g/C.b.g.
t
t
t
t
W
T3 Re-positioning time
W Wait
t Time

6.6.11 Interaction with pLoads

pRack pR300 can interact with the pLoads controller, which manages
power using a load cut-off function.
Interaction can be enabled and the related parameters set from main
menu branch C.a.d and C.b.d.
Interaction between pRack pR300 and pLoads uses digital inputs or the
supervisor. The digital inputs have higher priority, therefore if a digital
input is not active, the corresponding action is not produced even if
requested by the supervisor.
Two of the free digital inputs on pRack pR300 can be confi gured for
connection to two pLoads outputs, with each input being assigned one
of the following actions:
•
No action. Activation of the digital input has no infl uence on control.
•
Capacity limited to the current value. Activation of the digital input
limits the maximum control request; capacity can be reduced from
this value by the controller, but cannot exceed the current value at the
moment the digital input was activated for the entire time it remains
active, as shown in the fi gure:
Regulation request
Limit
•
Capacity limited to a % value, settable by parameter. As in the previous
case, the control request is limited at the top end, however to a fi xed
value set by parameter.
•
Decrease capacity by a % value, settable by parameter. Activation of
the digital input reduces the control request by a fi xed value set by
parameter, as shown in the fi gure:
Regulation request
Max
Min
•
By suitably setting this parameter based on system confi guration,
one compressor can be shut down; for example if there are three
compressors, by setting the decrease to 33%, activation of the input
stops one of the three compressors. Compressor shutdown and restart
respect the safety times.
The digital inputs confi gured are common to both lines, while for each
line a diff erent action can be associated with the same digital input.
In any case, the previous actions do not interfere with the pRack pR300
safety features, which always have priority over the actions set from
digital input.
Moreover, a suction pressure safety threshold has been introduced,
therefore the actions associated with the inputs are only enabled if the
pressure does not exceed this threshold (settable by parameter). After
the pLoads action has been disabled, it is necessary that the suction
pressure returns below the safety threshold for a setted time (higher than
30 s), before restoring the interaction between the two devices, so to the
regulation can be stabilize.
49
Digital input
time
Fig. 6.al
offset
digital input
time
Fig. 6.am
pRack +0300025EN rel. 1.3 - 17.12.2015
ENG