48
ENG
MPXPRO - + 0300055EN rel. 1.0 30/08/10
Defrost Running time (parameters d10, d11)
Running time is a special function that determines when the refrigeration
unit needs defrosting. In particular, it is assumed that if the evaporator
temperature measured by probe Sd remains continuously below a
certain set threshold (d11) for a certain time (d10), the evaporator may
be frozen and a defrost is activated. The time is reset if the temperature
returns above the threshold.
Par. Description Def Min Max UoM
d10 Defrost time in “Running time” mode
0 = function disabled
0 0 240 min
d11 Defrost temperature threshold in “Running
time” mode
-30 -50 50 °C/°F
dt1 End defrost temperature (read by Sd) 8 -50.0 50.0 °C/°F
dt2 End defrost temperature (read by Sd2) 8 -50.0 50.0 °C/°F
Tab. 6.g.i
d10
t
t
ON
Sd
DEF
OFF
d1
d11
Fig. 6.k
Key
Sd Defrost probe t Time
DEF Defrost
Important: for multiplexed hot gas defrosts, the setting is only
valid on the Master and the defrost is synchronized across the
Master/Slave network.
Pressure probe alarm management during defrost
(parameter d12)
During defrost and dripping, so as to avoid false pressure probe error
signals, errors are ignored. The supervisor update can also be disabled.
Par. Description Def Min Max UoM
d12 Pressure probe alarm management during
defrost
probe error supervisor update
0 disabled enabled
1 enabled enabled
2 disabled disabled
3 enabled disabled
003-
Tab. 6.g.j
Sequential stops (parameters dS1, dS2)
Par. Description Def Min Max UoM
dS1 Compressor o time in “Sequential stop”
defrost mode
0 0 45 min
dS2 Compressor operating time in “Sequential
stop” defrost mode
120 0 240 min
Tab. 6.g.k
Sequential stop mode is especially useful for high-normal temperature
refrigeration controllers, and is based on the intelligent stopping of
control to allow the evaporator to defrost naturally by the ow of
ambient air only, without activating the defrost output and consequently
the defrost heaters. If the function is enabled (parameter dS1>0), two
counters are activated:
• OFFTIME: counts down during the stop time and on hold during
control;
• ONTIME: counts down during control and on hold during the stop
time.
Two events may occur, with reference to the following gure:
1. OFFTIME is reset (instant C): OFFTIME and ONTIME are reset with
dS1 and dS2 value and the defrost is considered completed. Control
resumes;
2. ONTIME is reset (instant A): OFFTIME is reset with the default value
and the natural defrost starts, lasting the time dS1. At the end of the
defrost (instant B), OFFTIME and ONTIME are reloaded with dS1 and
dS2 value and control resumes;
C
OFFTIME=0
t
t
ON
1
CMP
regulation regulation
OFF
ONTIME=0
dS1
AB
t
regulationregulation defrost
ON
2
CMP
OFF
Fig. 6.l
Key
CMP Compressor t Time
The purpose is to stop control and allow natural defrosts only when
necessary.
Note: the setting of parameter F3 has no e ect. Evaporator fan
management depends on parameter F0.
Skip defrost (parameters d7, dn)
The function applies to defrosts that end by temperature, otherwise it
has no e ect. The Skip defrost function evaluates whether the defrost
duration is less than a certain threshold dn1 (dn2) and based on this
establishes whether or not the following defrosts will be skipped.
Par. Description Def Min Max UoM
d7 Skip defrost
0 = disabled; 1 = enabled;
001-
dn Nominal defrost duration for “Skip defrost” 75 0 100 %
dP1 Maximum defrost duration 45 1 240 min
dP2 Maximum secondary evaporator defrost
duration
45 1 240 min
Tab. 6.g.l
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