10
DKRCC.PS.RQ0.B7.02 /520H8832
© Danfoss A/S (AC-MCI / sw), 2014-11
Manual
Superheat Controller EIM 336
Using the MOP
In order to reduce the current to the compressor it is possible
to control the maximum operating pressure of the evaporator.
Evaporator pressure exceeds the “MOP” limit, the valve opening
degree is controlled by the MOP function which will keep the
pressure below the “MOP” limit. This function takes precedence
over the superheat control, so during MOP control the superheat
is not controlled.
The MOP function can be disabled by setting the “MOP” to
the maximum value (600 equalling 60.0 bar absolute). When
the pressure reaches the set MOP point, an increase in OD is
restricted. If the pressure reaches MOP + 0.5 Bar, an increase in
OD is prohibited, and instead the OD will start to decrease. If the
pressure goes below the MOP point, the controller will start to
regulate the superheat normally.
The MOP controller consists of a separate PI control, which
settings can be changed by setting “Kp MOP” and “Tn MOP”.
A large Kp will lead to a large change in opening degree even
at small changes in the evaporator pressure, but may lead to
instability. A large Tn will lead to a slow reacting system, while
a small Tn will lead to a fast reacting system.
Related parameters:
Symbolic name
PNU
Description
n11 MOP
3013
Maximum operation pressure. If Pe goes above this value, the controller will control on Pe, and not on superheat.
--- Kp MOP
3113
Kp proportional gain while in MOP control mode.
--- Tn MOP
3114
Tn integration time while in MOP control mode.
Using T
e
control
For applications with a need to de-humidify the evaporator, it
is possible to control on the saturated evaporator temperature
instead of the normal control signal. If the “T
e
Reference” register
is set to a value above 0, T
e
control is activated. T
e
and the 'T
e
Reference' to calculate a new reference for the superheat control.
The T
e
control consists of a separate PI control, which settings can
be changed by setting the gain, “Kp Te” and time constant, “T
n
T
e
”.
A large Kp will lead to a large change in the output even at small
changes in the evaporator temperature, but may lead to instability.
A large T
n
will lead to a slow reacting system, while a small Tn will
lead to a fast reacting system.
The MOP function is still active during T
e
control and it will assume
control, if the evaporator is above the “MOP” limit.
Related parameters:
Symbolic name
PNU
Description
--- Kp T
e
3115
Kp proportional gain while in Te control mode
---Tn T
e
3116
Tn integration time while in Te control mode
--- T
e
Reference
3117
Te reference while in Te control mode
Pressure Pe
MOP + 0.5
MOP
Normal regulation
Valve
Opening
Digree
At this pressure the OD
increases slower and
slower.
At this pressure the OD
no longer increases.
Beyond it the OD
decreases.
D
an
fo
ss
84B3084.11
Normal OD
Controlled OD
Force closed OD