Emerson XM678D, Operation And Installation Manual

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34 • XM678D I&O Manual 026-1219 Rev 3
the defrost in the whole multiplexed cabinet
according to the LMd parameter.
• Differential defrost: Selecting the dPA and dPb
probes and by changing the dtP and ddP
parameters, the defrost can be started when the
difference between dPA and dPb probes is lower
than dtP for all ddP time. This is useful to start
defrost when a low thermal exchange is detected. If
[ ddP = 0 ], this function is disabled.
19.3.2. Defrost Ending
• When defrost is started via rtC , the maximum
defrost duration is obtained from the Md parameter
and the defrost end temperature is obtained from the
dtE parameter (and dtS if two defrost probes are
selected).
• If dPA and dPb are present and [ d2P = Y ], the
device stops the defrost procedure when dPA is
higher than dtE temperature and dPb is higher than
dtS temperature.
At the end of defrost, the drip time is controlled
through the Fdt parameter.
19.4.Fans
19.4.1. Control With Relay
The fan control mode is selected by means of the FnC
parameter:
• C-n = running with the solenoid valve, OFF during
defrost
• C-Y = running with the solenoid valve, ON during
defrost
• O-n = continuous mode, OFF during defrost
• O-Y = continuous mode, ON during defrost
An additional parameter FSt provides the setting of
the temperature, detected by the evaporator probe,
above which the fans are always OFF. This can be
used to verify that air is circulated only if this
temperature is lower than set in the FSt .
19.4.2. Control With Analog Output
(If Present)
The modulating output [ trA = rEG ] works in a
proportional manner (excluding the first AMt
seconds where the fans speed is the maximum; 10
seconds is the minimum value). The regulation
setpoint is relative to the regulation setpoint and is
indicated by ASr , the proportional band is always
located above the [ SET + ASr ] value and its value is
PbA . The fans are at minimum speed AMi when the
temperature read by the fan probe is [ SET + ASr ] and
the fan is at maximum speed ( AMA ) when the
temperature is [ SET + ASr + PbA ].
19.5.Anti-Sweat Heaters
Anti-sweat heater regulation can be performed with
the on board relay (if OA6 = AC ) or with the analog
output (if present by setting trA = AC ). However, the
regulation can be performed in two ways:
• Without real dewpoint information: in this case the
default value for dewpoint is used ( SdP parameter).
• Receiving dewpoint from XWEB5000 system: the
SdP parameter is overwritten when a valid value for
dewpoint is received from XWEB. In case the
XWEB link is lost,
SdP is the value that will be used
for safety.
The best performance can be obtained using probe 4.
In this case, the regulation follows the chart illustrated
in Figure 19-2 :
Figure 19-1 - Control With Analog Output
Figure 19-2 - Anti-Sweat Heaters