Future Design MCT-CM User Manual Download

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MCT-CM

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9.2.3.2

After Defrost Switching

After defrost operation provides equal run time switching based on the user defined alternating switch interval.
When OEM configured for

‘After Defrost’ and no redundancy alarm condition exists, a defrost cycle will be

forced at each system switch time when

‘timed defrost’ is configured. If defrost is configured for timed process,

a defrost cycle will be forced at system switch only if required based on  the condition of the loop or monitor
point  configured.    Normal  defrost  cycles  will  take  place  based  on  timed  or  timed  process  settings  since  the
‘equal run time’ switching is typically longer than the system should run without a defrost cycle.

If  a  defrost  cycle  is  running  and  the  equal  run  time  switching  timer  has  elapsed,  the  defrost  cycle  will  be
completed, then the primary systems will switch.  If a redundancy alarm condition exists (process alarm, system
1/2 fail), defrost cycles will be performed under fail mode operation based on timed or timed process settings.

Pressing the demand Defrost button will perform a single defrost cycle based on defrost settings (during normal
switching  or  fail  mode  conditions).    Primary  systems  and  actual  system  digital  outputs  (1/2)  will  only  switch
when no redundancy alarm conditions exist and concurrent operation is not active.

9.2.3.3

Low Rise Backup Defrost Switching

Low rise defrost provides the same operation as “After Defrost” switching with one exception.  When defrost is
activated on the Primary system, the Backup system is automatically started in order to maintain temperature
while the Primary system is in defrost.  Once defrost is complete on the Primary system, it will be restarted and
the Backup system will continue to operate for a minimum time (the defrost Fan delay time as entered on the
Defrost screen).  Once the delay time has expired, the Backup system will automatically turn off.  This cycle will
continue until the equal run time switching timer has elapsed.

If  a  defrost  cycle  is  running  and  the  equal  run  time  switching  timer  has  elapsed,  the  Primary  system  will  be
turned off and the Backup system that was already running during defrost of the Primary system, will continue
operating and become the Primary system.  If a System Failure condition exists, defrost cycles will be performed
under fail mode operation based on Timed or Timed process settings; however, the failed system will be unable
to operate during defrost of the operating system, so a rise in temperature can occur during the defrost period.

9.2.4

System 1/2 Failure

If a system 1/2 failure occurs on alternating or concurrent systems, the MCT will always operate in fail mode on
the system that does not have a system failure. If both 1 and 2 system failures occur, the digital outputs
configured for

‘Redundant System 1 or 2’ will be de-energized. During any system failure (1/2 or 1 and 2), the

alarm must be reset from the main alarm screen and the condition cleared that caused the system failure.

Once the

alarm condition is acknowledged and cleared, the “Reset” button on the Redundancy screen must be

pressed in order for normal system operation to resume, at which point the backup system will become the
primary system. The user can switch from

‘Auto’ to ‘Manual’ mode at any time to run system 1 or 2 in manual

operation while performing maintenance on the systems.

NOTE:

System 1/2 failures are defined by the OEM configured digital input selections. When the assigned
alarm input(s) for the system is active, the system failure occurs. Consult your OEM configuration for
information on which inputs are configured for system 1/2 failure (if any).