Emerson XM678D, Operation And Installation Manual

Page: 36 / 76

28 • XM678D I&O Manual 026-1219 Rev 3
16.3.1. ON/OFF Temperature
Regulation [CrE = n]
1. Temperature regulation is ON/OFF and it depends
on the Setpoint and HY parameter (differential).
Valve is closed when the temperature reaches the
setpoint and open when the temperature is higher
than se differential.
2. With more pauses normally also the humidity is
larger.
3. Regulation pauses can be realized using the Sti and
Std parameters (during these pauses the valve is
closed).
16.3.2. Continuous Temperature
Regulation [CrE = Y] (With
Superheat Regulation)
1. The HY parameter becomes the temperature band
for PI control. A good default value is 5°C .
2. The regulation of injection is continuous and the
cooling output is always ON. The icon is always
ON except for the defrost phase.
3. The superheat is regulated following the SSH
parameter.
4. Regulation pauses can be realized using Sti and Std
parameters (during these pauses the valve is
closed).
5. Increasing the Int integral time can decrease the
speed of reaction of the regulator on the HY band.
16.3.3. Continuous Temperature
Regulation [CrE = Y] (Without
Superheat Regulation)
1. The HY parameter becomes the temperature band
for PI control. A good default value is 5°C .
2. The regulation of injection is continuous and the
cooling output is always ON. The icon is always
ON except for the defrost phase.
3. The superheat is not regulated because the valve is
at the end of the evaporator. There is another valve
at the beginning of the evaporator.
4. Regulation pauses can be realized using Sti and Std
parameters (during these pauses the valve is
closed).
5. Increasing the Int integral time can decrease the
speed of reaction of the regulator on the HY band.
16.4. Self Adaptive
Operating Mode -

AMS = YES
Auto-adaptive means to find and maintain the
condition of the lowest super heating according to the
load and environmental conditions present in a given
time on the evaporator.
The parameter
AMS enables the self adaptive mode
in the superheat regulation.
In this functioning the values of
Pb and inC
parameter are automatically set by the controller
according to the kind of applications and the response
of the system.
With the
AMS = YES, CrE must be set to NO .
The self adaptive algorithm does not affect the
functions related to the forced opening of the valve in
special situations, such as:
• Forced opening of the valve at start of regulation ,
parameter SFd (percentage) and SFd (time).
• Forced opening of the valve after defrost ,
parameter oPd (percentage) and Pdd (time).
16.5.Minimum Stable
Superheat Search -
AMS = YES, ATU = YES
With the parameter ATU , the minimum stable
superheat search function is enabled.
With
ATU = yES , controllers start searching the
minimum stable value for the SH. The minimum
admitted value in any case is LSH + 2°C (4°F). Take
it in consideration, before setting LSH value.
16.6.Valve Capacity
Reducing - MNF
Parameter
The parameter MnF reduce the capacity of the valve,
to fine tune the valve to the evaporator.
The regulation band is not affected from the
modification of the MnF parameter.