Carel Clima User Manual download pdf (Page 46)

46 “MPXPRO” +030220186 - rel. 1.0 - 22.05.2007

{

Interval in which

the function is ON

Controlled

temperature (°C)

(Ton= st e rd) cabinet

differential (°C)

(Tf= st+rd/2) Function

intervention threshold (°C)

(Toff=st) Cabinet

set point (°C)

Time

Tf= set point (”st”) + differential (”rd”) /2

Fig. 6.g

E N G L I S H

MPXPRO, with PID control, tends to maintain the actual superheat, calculated based on the probe rea-

dings, around the value set for this parameter. This is done by gradually varying the opening of the valve

based on the difference between the actual superheat and the set point.

Important: The set point value calculated depends on the quality of the installation, the position of the

probes and other factors. Consequently, depending on the installation the set point read may deviate

from the actual value. Set point values that are too low (2 to 4 K) may cause problems involving the

return of liquid refrigerant to the compressor rack.

cP1 EEV – ADV Initial valve position when control starts

Code UOM Min Max Def.

cP1 % 0

100 30

This is used to set the position of the valve as a percentage when control starts. High values ensure

intense and immediate cooling of the evaporator when each call is sent, however may cause problems

if the valve is oversized with reference to the cooling capacity of the unit. Low values, on the other hand,

allow a more gradual and slower action.

Pdd EEV–ADV Initial valve position maintenance time after defrost

Code UOM Min Max Def.

Pdd min 0

30 10

At the end of a defrost, during the dripping phase, the expansion valve can be forced open to the initial

value set for “cP1” for a time equal to “Pdd”. This means greater immunity of the instrument to return of

liquid to the compressor rack due to an excessively high evaporator temperature.

PSb EEV – ADV Valve standby position

Code UOM Min Max Def.

PSb steps 0

400 7

This indicates the position, as the absolute number of steps, that the valve must move to after having com-

pletely closes, to restore the elastic operating conditions of the valve spring, by releasing the compression

(for stepper valve only).

Note: the value of this parameter represents the absolute position of the valve during the closing phase

(value read using the advanced parameter ‘PF’).

Phr EEV–ADV Enable fast update of the valve parameters to supervisor

Code UOM Min Max Def.

Phr ﬂag 0

1 0

This is used to enable the fast update to the supervisor of the variables relating to the electronic expan-

sion valve, such as:

PF - absolute position in number of steps (for stepper valves only),

Po1 - superheat

Po2 - position as a percentage,

Po3 - superheated gas temperature,

Po4 - saturated evaporation temperature,

Useful in commissioning phase or start-up:

Phr = 0: fast update disabled (update every 30 s)

Phr = 1: fast update enabled (update every 1 s)

OSH EEV – ADV Superheat Offset for modulating thermostat

Code UOM Min Max Def.

OSH K 0.0

60.0 0.0

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 unit

control temperature and affects the cooling capacity of the electronic valve. In particular, the function is

activated when the control temperature falls below half of the differential rd. In this band, the superheat

set point P3 is increased by the parameter OSH. The effect of this action is the gradual advanced closing

of the electronic valve, which makes the decrease in temperature inside of the refrigeration unit 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 ﬂow of

refrigerant.

Note:

The action of OSH is weighted, based on the difference between the temperature set point and the

control temperature. The lower the difference, the greater the action of OSH and vice-versa.

OSH is active in a band at maximum equal to half of the differential rd

With double thermostat active, the action of OSH will be determined by the thermostat with the lower

difference between the set point and the actual temperature.

•

B@ rd: Temperature set point differential, p. 27

A@ P3- EEV - PID superheat set point, p. 45

B@ rd: Temperature set point differential, p. 27

A@ P3- EEV - PID superheat set point, p. 45

A@ PF: EEV - ADV passi apertura valvola, p. 51

In a network of instruments, Phr should not be enabled on all

the instruments indiscriminately, but rather one at a time and

only for service and test operations

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