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XM Circuit Control Software Overview
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ing to the associated XM case controllers.
Defrost Start Mode
Defrosts may be initiated with one of the following
methods - Numbered or Scheduled.
•
Numbered
- the starting time of the first defrost
(called Reference Time) is defined by the user and
all the subsequent defrosts are equally spaced out
throughout a 24-hour period. For example, if four
defrosts are specified with a reference time of
00:00, the remaining three defrosts will begin at
06:00, 12:00, and 18:00. Up to 24 numbered
defrosts may be specified.
•
Scheduled
- the absolute start time for each defrost
is specified by the user. Up to 12 scheduled defrosts
may be specified.
Days Between Defrost
The
DaysBetweenDfr
parameter specifies the number
of days to skip scheduled defrosts. This feature is useful
for cases that do not require a defrost cycle every day. If
set to zero, defrosts will occur every day. If set to one,
defrosts will occur every other day. If set to two, defrosts
will occur every after two days. The user may specify up
to six days to skip defrosts.
5.31.3.5 Case States
The XM Circuit application provides a circuit status
output (CASE STATE OUT) to indicate the mode of oper-
ation of the circuit.
The XM Circuit application supports the following
case states:
The XM Circuit application determines the state of
each associated case controller by evaluating CASE REFR
STA and CASE DEFR STA. Based on the value of these
two input properties, one of the three case states listed in
Table 5-17
is selected and written to the corresponding
CASE STATE OU output property.
5.31.3.6 Case Type
The
Case Type
parameter permits the user to select the
type of refrigerated case that will be used for the XM Cir-
cuit application. Based on this setting, the case tempera-
ture setpoint and certain defrost parameters will be set to
suitable values.
5.31.4 Application Advisory
The following advisories are generated by the XM Cir-
cuit application:
• Combined Case Temperature High/Low
• Product Temperature High/Low
• Defrost did not start
5.31.4.1 Synchronized Alarm Parameters
The XM Circuit application will synchronize the Case
Alarm High and Low setpoints with associated XM
devices. The circuit will not perform the alarming func-
tionality for Case Temperature as it is handled in each XM
device.
Because XM devices support relative and absolute
alarming for Case Temperature, the XM Circuit will sup-
port the
Case Alarm Hi
and
Case Alarm Lo
parameters
as either temperature or

temperature Engineering Units.
5.31.5 Application Commands
The following application commands will be sup-
ported by the XM Circuit application:
5.31.5.1 Start Defrost
When the user selects this command, a defrost cycle is
immediately initiated. The START DEFR OUT output will
turn ON and will stay ON for the duration specified in the
Min Defr Time
parameter. If at anytime during this period
the user issues a Stop Defrost command, the START
DEFR OUT output will immediately turn OFF.
5.31.5.2 Stop Defrost
When the user selects this command, a defrost cycle is
immediately stopped. The STOP DEFR OUT output will
turn ON and will stay ON for a period of one minute, and
then will switch OFF. If at anytime during this period the
State Description
Off
The circuit is shut down. All
associated case controllers are neither
refrigerating nor defrosting.
Refrigeration
The circuit is refrigerating. Most
associated case controllers are in the
refrigeration state (maintaining case
temperature setpoint).
Defrost
The circuit is in defrost. Most
associated case controllers are in a
defrost cycle. (The defrost cycle
includes several sub-states, for
example, pump down, drip, and more.)
Table 5-17 - Case States
NOTE: The behavior of the START DEFR
OUT output is the same whether it is started by
the Start Defrost command or by a regularly
scheduled defrost.