Fig.5.z
Ref. Description
A Relay output
B 0-10 Vdc output
rHu
Manual anti- sweat heater activation
percentage
Ref. Description
rHt Manual anti-sweat heater activation period
t Time
5.6 Electronic
valve
Introduction
MPXone manages an electronic expansion valve using an external driver connected to the Fieldbus port.
Using this driver, the following can be set:
l superheat set point;
l type of refrigerant;
l protectors - low superheat (LowSH), maximum evaporation pressure (MOP), minimum evaporation
pressure (LOP).
Code Description Def Min Max UOM User
User
terminal
P1
Electronic valve type
0 = not used/thermostatic valve
1 = reserved
2 = CAREL E2V valve (suction temp. probe connected)
3, 4, 5 = reserved
6 = CAREL E2V valve (suction temp. probe on external driver)
0 0 6 - S YES
MPXone has been designed to manage one electronic expansion valve on one evaporator.
The superheated gas temperature probe and the saturated evaporation temperature probe can be
connected directly to MPXone or to the external driver, setting parameter P1 to 2 or 6.
Note:
l see "Introduction" for the models of temperature and pressure probes to be installed;
l CAREL suggests using ratiometric probes to read the evaporation pressure, which is automatically
converted to saturated temperature based on specific tables for the type of refrigerant used.
Description of operation
The values read by the probes described above are called:
l tGS = superheated gas temperature;
l tEu = saturated evaporation temperature, converted from the pressure.
Superheat is calculated based on these values:
l SH = tGS - tEu
MPXone Medium manages the proportional opening of the electronic expansion valve, adjusting the flow
of refrigerant in the evaporator, so as to maintain the superheat around the value set for advanced
parameter P3 (superheat set point). The opening of the valve is controlled independently of normal
temperature control. When there is a cooling request (the compressor/solenoid valve relay is activated),
control of the electronic valve is also activated. If the superheat value read by the probes is greater than
the set point, the valve is opened proportionally to the difference between the values. The speed of
variation and the percentage of opening depend on the PID parameters set. Opening is continuously
modulated based on the superheat value, with PID control.
Note: all the references relating to control of the electronic valve are based on the use of a CAREL E2V
electronic expansion valve. The descriptions therefore consider the steps of the stepper motor used
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