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Technical Information
Figure 28: Defrost Phases
8.3
Defrost process
The defrost process can be requested using the following functions:
▪
Using the interval timer: A timing element is activated and requests a defrost cycle after expiration of
the configured period. The time interval is controlled using the
26
“Defrost interval"
configuration
parameter. If this parameter is set to "0", there is no time-based defrost request.
▪
Using a network command: By setting the writing variable
521
“Defrost command“
to a value other
than zero, a defrost request can be issued. This variable is automatically re-set to "0" once a defrost
request is detected.
▪
Via Modbus: Sending a defrost request causes a defrost cycle to start. This is the case when the
defrost request output is activated for one of the controllers in the defrost synchronization chain and
the corresponding DIP switch is active.
▪
Using the display module.
▪
Using the real-time clock.
In general: when a defrost request is detected, the defrost request output activated using the DIP switch is set
and triggers a defrost request for all other controllers of the same defrost synchronization chain.
8.4
Termination of the defrost process
The cancellation mode for the defrost process is set using the
27
“Defrost termination (dt)“
configuration
parameter.
If the mode is set to "... temperature or time", the defrost cycle is stopped as soon as the configured
temperature rises above the corresponding value of the predefined
28
“Defrost limit temperature (daytime
operation)
“
or
29
“Defrost limit temperature (nighttime operation)“
configuration parameter
In any case, the defrost cycle is stopped after a delay that is entered in the
30
“Defrost time limit (daytime
operation)
“
or
31
“Defrost time limit (nighttime operation)”
configuration parameters.
8.5
Defrost monitoring
The defrost status can be determined using 3 different methods:
▪
The general application state "defrost running" is initiated when the defrost cycle is started and
canceled at the end of the synchronization phase.
▪
The read-only "defrost running" variable is set to "1" in the event of a defrost request and re-set to "0"
after the end of the synchronization phase.
End of defrost cylce
End of defrost
Waiting for other
equipment
Set interval timer to defrost interval
Duration of defrost phase variable
Max. time defined by parameter: Defrost time limit
(daytime or nighttime operation)
Duration of drain
phase defined by
parameter: Draining
delay
Normal operation
"Normal defrost"
"Synchronized defrost"
Start of defrost cylce
Set interval timer to defrost interval
Duration of defrost phase variable
Max. time defined by parameter: Defrost time limit
(daytime or nighttime operation)
Duration of drain
phase defined by
parameter: Draining
delay
Normal operation
Start of defrost cylce
End of defrost cylce
Max. idle time for
other cabinets to
finish defined in
cfg 82
