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MCT-CM
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9.2.1 Concurrent Redundancy Switching
When redundancy is active (OEM configured enable output(s) on), any digital outputs configured for
“Redundant System 1’ or ‘Redundant System 2’ that correspond with the selected primary system will be turned
on. The opposing system then becomes the ‘backup’ system by default.
When the redundancy process alarm exists, the MCT will run the backup system concurrently with the primary
system until the minimum concurrent run timer expires, or until the process alarm condition no longer exists. If
the redundancy alarm is set for latching, the user must press the alarm reset button on the main alarm screen
to acknowledge the alarm in order for it to clear. The backup system will then shut down automatically after the
minimum time period (user defined) expires if the process alarm no longer exists. The user can switch from
‘Auto’ to ‘Manual’ at any time and select the primary system or run a single system in manual mode.
9.2.2 Alternating Redundancy Switching
When redundancy is active (OEM configured enable output(s) on), any digital outputs configured for
“Redundant System 1’ or ‘Redundant System 2’ that correspond with the selected primary system will be turned
on. The opposing system th
en becomes the ‘backup’ system by default.
When the redundancy process alarm exists, the MCT will switch to the backup system (turn off the primary
system output and turn on the backup system output) and operate in fail mode on the backup system until the
alarm condition is cleared and the “Reset” button is pressed. If the redundancy alarm is set for latching, the
user must press the alarm reset button on the main alarm screen to acknowledge the alarm in order for it to
clear. Once the alarm condition is clear
ed and the redundancy “Reset” button is pressed, the backup system
becomes the primary system and normal redundancy operation resumes. The user can switch from
‘Auto’ to
‘Manual’ at any time to select primary systems or run a single system in manual mode.
9.2.3 Equal Run Time Switching
Equal run time switching (when no redundancy alarms exist) is provided for both alternate and concurrent
systems. Equal run time switching is OEM configured for
‘Before Defrost’ or ‘After Defrost’ operation.
NOTE: If defrost is not configured, equal run
time switching (if configured) will correspond to the ‘After Defrost’
mode of operation; however, no defrost action would take place prior to the system switch.
9.2.3.1 Before Defrost Switching
Before defrost operation provides equal run time switching at each
“timed” defrost cycle. No defrost cycle is
performed during system switching in this mode. Since system switching is done at each defrost cycle, the
system not running will naturally defrost due to normal ambient conditions between defrost intervals. If a
redundancy alarm occurs (process alarm, system 1/2 fail), defrost cycles will be performed under fail mode
operation based on timed or timed process defrost settings.
Pressing the demand defrost button while redundancy alarm conditions exist, will perform a single defrost cycle
based on timed or timed process defrost settings. Pressing the demand defrost button while no redundancy
alarm conditions exists, will switch between system 1 and 2 with no defrost cycle being performed. Primary
systems and actual system digital outputs (1/2) will only switch when no redundancy alarm conditions exist and
concurrent operation is not active.
When a defrost cycle is performed and the system is running in concurrent mode due to a redundancy alarm,
the backup system will be turned off and the primary system will go through the defrost cycle. The redundancy
alarm will be reset when defrost activates, so that upon completion of the defrost cycle, the redundancy alarm
delay (if any) will have to expire again prior to turning on the backup system again. This provides for a ‘smart
recovery’ action in the event that the redundancy alarm was due to a frozen evaporator.