User manual

52
ENG
MPXPRO - + 0300055EN rel. 1.3 07/03/13
High values ==> slow and less reactive valve (e.g. 400 for CO
2
- carbon
dioxide applications)
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 ==> fast variations
Low values ==> limited variations
P6 = 0 ==> diff erential action disabled
Example. For CO
2
- carbon dioxide applications: P6=5
Smooth Lines function
The new Smooth Lines function is used to optimise evaporator
capacity based on actual cooling demand, allowing more eff ective and
stable control of cabinet temperature. Unlike the existing modulating
thermostat (OSH), this function completely eliminates traditional on/
off control, modulating the temperature inside the cabinet exclusively
using the electronic expansion valve, and adjusting the superheat set
point by adopting accurate PI control based on the eff ective control
temperature.
The main features are:
• The superheat set point for managing the electronic expansion valve
can vary between a minimum (traditional set point P3) and maximum
limit (P3+PHS: maximum off set) using PI control (pre-confi gured),
based on the control temperature and how far this is from the
corresponding set point St
• The temperature inside the cabinet can fall slightly below the set point
St, without stopping the main control, however simply closing the
electronic valve
• Temperature control (and consequently the solenoid valve relay)
therefore remains active at all times, while the electronic expansion
valve stops the fl ow of refrigerant into the evaporator
• It is easy to use, as it is the instrument itself that automatically
adapts control based on current operation, without requiring special
parameter settings
The main benefi ts are
• No swings in temperature and superheat when reaching the set point
• Stable temperature and superheat control
Maximum energy savings by stabilising the load
t
Temp. set
SH set
MAX
MIN
Fig. 6.t
Par Descrizione Def Min Max UM
PSM Smooth Lines - Enable function 0 0 1
PLt Smooth Lines - Off set to stop control below
set point
2.0 0.0 10.0 °C/°F
PHS Smooth Lines - Maximum superheat off set 15.0 0.0 50.0 K
Note: Smooth Lines is not compatible with traditional Floating
Suction control, and must be used with the new Rack Smart Set
algorithm
6.10 Protectors
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 the 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). When
low superheat status is activated, the local solenoid valve can be forced
closed (parameter P10).
Par. Description Def Min Max UoM
P7 LowSH: low superheat threshold 7.0 -10.0 P3 K
P8 LowSH: integration time
0 = function disabled
15.0 0.0 240.0 s
P9 LowSH: alarm delay
0 = alarm disabled
600 0 999 s
Tab. 6.ax
t
B
P9
t
t
ON
P7
LowSH
SH
OFF
ON
ALARM
OFF
Fig. 6.u
Key
SH Superheat P7 LowSH threshold
LowSH Low superheat protection P9 Alarm delay
ALARM Alarm t time
MOP Maximum evaporation pressure
When starting or restarting an installation, the compressors may
not be able to satisfy the simultaneous refrigeration requirements
of all the refrigeration utilities in the installation. 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.
Important: if this action causes the complete closing of the
electronic valve, the solenoid valve is also closed, even if this is a
network solenoid valve, when enabled. The alarm signal with the
message ‘MOP’ on the display is delayed from the activation of the
protection function and is automatically reset as soon as the saturated
temperature falls below the threshold.
Par. Description Def Min Max UoM
PM1 MOP: saturated evaporation temperature
threshold
50.0 -50.0 50.0 °C/°F
PM2 MOP: integration time 10.0 0.0 240.0 s
PM3 MOP: alarm delay
0 = function disabled
0 0 999 s
PM4 MOP function delay when starting
control
2 0 240 s
PM5 MOP: enable close solenoid valve
(optional)
001-
Tab. 6.ay