31
ENG
Heos +0300078EN - rel. 1.6 - 23.11.2017
Par. Description Def U.M.
Min Max
P4 PID: EEV proportional gain 15.0 0.0 100.0
P5 PID: EEV integral time
0 = function disabled (NO);
150 s 0 999
P6 PID: EEV derivative time
0 = function disabled (NO);
5.0 s 0.0 100.0
P4: this represents the amplifi cation factor. It determines an action that
is directly proportional to the diff erence between the set point and
the actual superheat value. It acts on the speed of the valve, in terms
of steps/°K. The valve moves P4 steps for every degree variation in the
superheat, opening or closing whenever the superheat increases or
decreases respectively. It also acts on the other control factors, and is valid
in both normal control and with all emergency control functionsa.
• High values ==> fast and reactive valve
• Low values ==> slow and less reactive valve.
P5: this represents the time required by the controller to balance the
diff erence between the set point and the actual superheat. It practically
limits the number of steps that the valve completes each second. It is
only valid during normal control, the special functions in fact have their
own integral time.
• High values ==> slow and less reactive valve
• Low values ==> fast and reactive valve
• P5 = 0 ==> integral action disabled
P6: this represents the reaction of the valve to variations in the superheat.
It amplifi es or reduces variations in the superheat value.
• High values ==> rapid variations
• Low values ==> limited variations
• P6 = 0 ==> diff erential action disabled
6.10 Protection functions
LowSH Low superheat
To prevent too low superheat values that may cause the return of
liquid to the compressor or system instability (swings), a low superheat
threshold can be defi ned, below which a special protection function
is activated. When the superheat falls below the threshold, the system
immediately enters low superheat status and activates a control action,
in addition to normal control, with the aim of closing the electronic valve
more quickly. In practice, the intensity of system “reaction” is increased.
If the device remains in low superheat status for a certain period, a low
superheat alarm is activated, with the display showing the message ‘LSh’.
The low superheat signal features automatic reset, when the condition is
no longer present or the controller is switched off (standby).
Par. Description Def U.M.
Min Max
P7 LowSH: low superheat threshold 2.0
(35.6)
°C
(°F)
0.0
(32.0)
30.0
(86.0)
P8 LowSH: EEV low superheat integral time
0 = function disabled (NO);
10 s 0.0 999
P9 LowSH: EEV low superheat alarm delay
0 = function disabled (NO);
120 s 0 300.0
time
TempSH
ON
OFF
ALARM
ON
P7
OFF
LowSH
P9
Fig. 6.z
Key
SH Superheat P7 Low SH protection threshold
LowSH Low superheat protection P9 Alarm delay
ALARM Alarm
MOP Maximum evaporation pressure
When starting or restarting a system, the compressors may not be able
to satisfy cooling demand. This may cause an excessive increase in the
evaporation pressure and consequently the corresponding saturated
temperature. When the evaporation pressure, expressed in degrees
(saturated), rises above the threshold, after a certain settable time the
system enters MOP protection status: PID superheat control is stopped
and the controller starts gradually closing the valve with an integration
action to return the evaporation pressure below the threshold. The
protection function has been designed to allow a gradual return to
normal operating conditions, that is, when the critical conditions have
ended, the controller temporarily operates with a higher superheat set
point until the function is automatically reset.
Par. Description Def U.M.
Min Max
PM1 MOP 15.0
(59.0)
°C
(°F)
LOP 30.0
(86.0)
PM2 MOP: High evaporation temperature integral
time
20.0 s 0.0 999
PM3 MOP: High evaporation temperature alarm delay
0 = function disabled (NO);
240 s 0 300.0
time
ON
OFF
ALARM
ON
OFF
PM1
MOP
T
evap
PM3
Fig. 6.aa
Key
T_EVAP Evaporation temperature PM1 MOP threshold
MOP MOP protection PM3 Alarm delay
ALARM Alarm
PM1 represents the maximum evaporation pressure, expressed in
degrees (saturated), above which the MOP protection and alarm are
activated (each with its own delay times). There is a gradual return to
normal operation, to avoid the critical situations arising again.
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