Carel MPXPRO User Manual page 38

ENG
Example. The following fi gure shows an installation with an MPXPRO
Master controller and an MPXPRO Slave controller, highlighting the hot
gas, intake and equalizing valves that are activated in the cycle.
SV
M
EEV
M
SV
E
M
HGSV2
HGSV1
SV
M
EEV
M
SV
E
M
HGSV4
HGSV3
Key
SSu Suction valve
EEV Electronic expansion valve
CMP Compressor
E Fan-forced evaporator
SV Solenoid valve
Note:
For hot gas defrosts, in every Master/Slave network:
• depending on parameter dHG the equalizing valve may be closed or
open;
• local defrosts are not possible;
• the hot gas valve is always and only local (one for each controller);
• the liquid solenoid valve may be local or network;
• the suction and equalizing valve may be local or network;
• the end of a hot gas defrost must be synchronized;
• the change from one phase to the next is always synchronized
between all controllers;
• the durations of the various phases are controlled by the parameters
set on the Master, the corresponding parameters on the Slaves are not
considered.
The defrost starts:
• by setting the event and the start mode, with a maximum of 8 defrosts
each day (parameters td1 to td8). The real time clock (RTC) must
be available, meaning this is always possible on the Master, which
then sends the synchronized requests to the Slaves. If independent
programming is required on the Slaves these must also be installed
with RTC cards;
• from the supervisor, which sends the defrost call to the Master
controller, and this sends it in turn to the Slaves;
• via digital input: for Master Slave networks, a network defrost is
activated.
The defrost ends:
• when the defrost probe measures a temperature greater than the end
defrost temperature dt1;
• when no defrost probe is used, the defrost ends after a maximum time,
set by parameter dP1.
Warnings
If the multiplexed hot gas defrost is set, check any possible
consequences of local defrosts performed by individual units that
are not synchronized with the remaining units in the multiplexed group.
MPXPRO - + 0300055EN rel. 1.0 30/08/10
MASTER
CAREL MPX PRO
!
MPXPRO
SSu
M
ESu
P T
M
SLAVE
CAREL MPX PRO
!
MPXPRO
SSu
M
P
T
ESu
M
Fig. 5.n
ESu Equalizing valve
P Evaporation pressure (PEu)
HSGV1 to 4 Hot gas valves
Superheated gas temperature
T
(tGS)
SV Solenoid valve
The installer is responsible for evaluating the eff ects on the multiplexed
system if one of the following events occurs:
• a unit in a multiplexed group performs a local hot gas defrost while the
other multiplexed units continue normal control;
• a multiplexed group starts a hot gas defrost while one of the units is
offl ine, and then continues control, or is OFF, if the safety procedure is
activated (parameter A13).
In particular, it is recommended to check the settings of the parameters
that may cause or allow unsynchronized defrosts between a Master and
its Slaves:
• d2: end defrost synchronized by the Master; in general, this parameter
should be set to 1 on the Master and the Slaves in the multiplexed
group (synchronized end defrost);
• dI: maximum interval between consecutive defrosts; this parameter
must be set to 0 on all units connected in Master Slave confi guration,
to prevent unsynchronized defrosts from being performed if the tLAN
is offl ine;
• d5: defrost delay on start-up; this delay must be set in the same way
on all the units;
• H6: terminal keypad lock confi guration; this should be set to 2 on the
Master and the Slaves to avoid starting local defrosts from the keypad.
In addition to setting parameter A13 to 1 (Enable hot gas safety procedure
for Slave offl ine), the safety procedure is also activated, switching a Slave
offl ine if it no longer communicates with its Master.
Maximum interval between consecutive defrosts
(parameter dI)
Par. Description
dI Maximum interval between consecutive
defrosts
Parameter dI is a safety parameter used to perform cyclical defrosts
every "dI" hours, even without the Real Time Clock (RTC). It is also useful
if the LAN or RS485 serial network is disconnected. At the start of each
defrost, irrespective of the duration, an interval starts being counted. If
this interval exceeds dI without a defrost being performed, one is started
automatically. The count is always active even if the controller is OFF. If
set on Master controller, the parameter has eff ect on all the sub-LANs
connected, if set on a Slave controller, it only has an eff ect locally.
Example: if there is an RTC fault, the defrost programmed by td3 is not
performed, and after the safety time dI a new defrost starts.
ON
DEF
OFF
td1
td2
Key
Maximum interval between consecutive
dI
defrosts
td1 to td3 Programmed defrosts
38
Def Min Max
8 0 240
Tab. 5.t
dl
t
td3
Fig. 5.o
t time
DEF Defrost
UoM
hour