Code Description Def Min Max UOM User
User
terminal
Pdd Initial valve position maintenance time after defrost 10 0 30 min S NO
Support saturated temperature for pressure probe error (parameter P15)
In the event of a pressure/saturated evaporation temperature probe error, this represents the constant
value used by the device to simulate the probe reading. In centralised systems, the evaporation pressure
is determined by the compressor rack set point. Once this set point has been set for P15, control can
continue, even if not in perfect conditions, in emergency situations.
Code Description Def Min Max UOM User
User
terminal
P15 Support saturated temp. for press. probe error -15 -50 50 °C/°F M NO
PID control (parameters P4, P5, P6)
The opening of the electronic valve is controlled based on the difference between the superheat set
point and the actual superheat calculated by the probes. The speed of variation, reactivity and the ability
to reach the set point depend on three parameters:
l Kp = proportional gain, parameter P4;
l Ti = integral time, parameter P5;
l Td = derivative time, parameter P6;
The ideal values to be set vary depending on the applications and the utilities managed, nonetheless
default values are proposed that allow good control in the majority of cases.
For further details, refer to classic PID control theory.
Code Description Def Min Max UOM User
User
terminal
P4 Proportional gain 15 0 100 - S NO
P5
Integral time
0 = function disabled
150 0 900 s S NO
P6
Derivative time
0 = function disabled
5 0 100 s S NO
l P4: this represents the amplification factor. It determines an action that is directly proportional to the
difference between the set point and the actual superheat value. It acts on the speed of the valve, in
terms of steps/°C. The valve moves P4 steps for every degree centigrade variation in superheat,
opening or closing whenever the superheat value increases or decreases respectively. It also acts on
the other control factors, and is valid in both normal control and with all emergency control functions.
High values ==> fast and reactive valve (e.g. 20 for CO2 - carbon dioxide applications).
Low values ==> slow and less reactive valve.
l P5: this represents the time required by the controller to balance the difference between the set
point and the actual superheat. In practical terms it 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 (e.g. 400 for CO2-carbon dioxide
applications)
Low values ==> fast and reactive valve P5 = 0 ==> integral action disabled
l P6: this represents the reaction of the valve to variations in superheat. It amplifies or reduces variations
in superheat.
High values ==> fast variations
Low values ==> limited variations
P6 = 0 ==> differential action disabled
Example: for CO2 - carbon dioxide applications: P6 = 5
Smooth Lines function
The smooth lines function optimises evaporator capacity based on actual cooling demand, allowing more
effective and stable control of the showcase. The function completely eliminates traditional on/off control
cycles, modulating the temperature exclusively using the electronic valve; superheat set point is
controlled through a precise PI control algorithm based on the actual control temperature. The main
features are:
76|5. Functions
MPXone +0300086EN rel. 1.0– 04.09.2018
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