User manual

51
ENG
MPXPRO - + 0300055EN rel. 1.3 07/03/13
Phr = 1: fast update enabled (update every 1 s).
Par. Description Def Min Max UoM
Phr Enable fast update of the valve parameters
to supervisor
0 = fast update disabled
001-
Tab. 6.at
Important: in the event of power failures, parameter Phr will be
reset to zero.
Superheat o set for modulating thermostat (parameter
OSH)
This function is used to reduce or completely eliminate the typical
temperature swings caused by sudden activation/deactivation of the
solenoid valve. The function is activated based on the refrigeration
controller control temperature and aff ects the cooling capacity of
the electronic valve. In particular, the function is activated when the
control temperature falls below half of the diff erential rd. In this band,
the superheat set point P3 is increased by a term proportional to the
parameter OSH. The eff ect of this action is the gradual advanced closing
of the electronic valve, which makes the decrease in temperature inside
of the refrigeration controller slower and more stable. In this way, the
actual temperature of the cabinet can be kept very stable and near the
set point, without ever having to close the solenoid valve, but rather by
simply controlling the fl ow of refrigerant.
t
t
St+rd
Sreg
St+rd/2
ON
OFF
F
St
Fig. 6.p
Key
Sreg Control probe t time
F
Modulating thermostat
function
Note:
• The action of OSH is weighted, based on the diff erence between the
temperature set point and the control temperature. The lower the
diff erence, the greater the action of OSH and vice-versa.
• OSH is active in a band at maximum equal to half of the diff erential rd
With double thermostat:
• the action of OSH will be determined by the thermostat with the lower
diff erence between the set point and the actual temperature;
• the highest contribution is used, Tf= st + rd/2 or Tf2= St2 + rd/2, as
there are two bands.
Par. Description Def Min Max UoM
OSH Superheat off set for modulating thermo-
stat (0 = function disabled)
0.0 0.0 60.0 K
Tab. 6.au
Example
OSH too low
t
St+rd
Sreg
St+rd/2
St
Fig. 6.q
OSH too high
t
St+rd
Sreg
St+rd/2
St
Fig. 6.r
OSH ideale
t
St+rd
Sreg
St+rd/2
St
Fig. 6.s
Key:
Sreg=control probe St=set point
rd = diff erential t= time
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.
Par. Description Def Min Max UoM
P15 Support saturated temperature for pressu-
re probe error
-15.0 -50.0 50.0 °C/°F
Tab. 6.av
PID control (parameters P4,P5,P6)
The opening of the electronic valve is controlled based on the diff erence
between the superheat set point and the actual superheat calculated by
the probes. The speed of variation, the reactivity and the ability to reach
the set point depend on three parameters:
Kp = proportional gain, parameter P4;
Ti = integration time, parameter P5;
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.
Par. Description Def Min Max UoM
P4 Proportional gain 15.0 0.0 100.0 -
P5 Integration time
0 = function disabled
150 0 900 s
P6 Derivative time
0 = function disabled
5.0 0.0 100.0 s
Tab. 6.aw
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/°C. The valve moves P4 steps for every degree centigrade 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 functions.
High values ==> fast and reactive valve (e.g. 20 for CO
2
- carbon dioxide
applications).
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 integration time.