15
ENG
“EVD ice” +0300038EN - rel. 1.1 - 23.04.2018
Example 1:
The pressure read is 20 barg this will be immediately
converted to the corresponding value of 290 psig.
Example 2:
The “superheat set point” parameter set to 10 K will be
immediately converted to the corresponding value of 18 °F.
Access to the Mode (operating mode) parameter (par. IA)
To avoid accidental modification of the controller’s operating mode, it is
possible to disable the access to the corresponding parameter.
Par. Description
Def. Min. Max. UoM
IA
Enable operating mode modification
0/1 = yes/ no
0
0
1
-
Number of control steps (par. U3)
Total number of steps between the valve fully closed and fully open
position
Par. Description
Def. Min. Max. UoM
U3 Number of valve control steps
1 / 2 = 480/960 steps
1
1
2
-
Digital input
The function of the digital input can be set by parameter:
Par. Description
Def. Min. Max. UoM
di
DI configuration
1=Start/Stop regulation
2=Regulation backup
1
1
2
-
Start/stop regulation:
•
digital input closed: control active;
•
digital input open: control in standby (see the paragraph “Control
states”).
Important:
this setting excludes activation/deactivation of control
via the network. See the following function.
Regulation backup:
if there is a network connection and communication
fails, the driver checks the status of the digital input to determine whether
control is active or in standby.
6. PROTECTORS
These are additional functions that are activated in specific situations that
are potentially dangerous for the unit being controlled. They feature an
integral action, that is, the action increases gradually when moving away
from the activation threshold. They may add to or overlap (disabling)
normal PID superheat control. By separating the management of these
functions from PID control, the parameters can be set separately, allowing,
for example, normal control that is less reactive yet much faster in
responding when exceeding the activation limits of one of the protectors.
6.1 Protectors
The protectors are 3:
•
LowSH, low superheat;
•
LOP, low evaporation temperature;
•
MOP, high evaporation temperature;
The protectors have the following main features:
•
activation threshold: depending on the operating conditions of the
controlled unit, this is set in Service programming mode;
•
integration time, which determines the intensity (if set to 0, the
protector is disabled): set automatically based on the type of main
control;
•
alarm, with activation threshold (the same as the protector) and
timeout (if set to 0 disables the alarm signal).
Note:
The alarm signal is independent from the effectiveness of
the protector, and only signals that the corresponding threshold has
been exceeded. If a protector is disabled (null integration time), the
relative alarm signal is also disabled.
Each protector is influenced by the proportional gain parameter (CP) of
PID superheat control. The higher is the value of CP, the more intensely
the protection will react.
Characteristics of the protectors
Protection
Reaction
Reset
LowSH
Intense closing
Immediate
LOP
Intense opening
Immediate
MOP
Moderate closing
Controlled
Tab. 6.a
Reaction:
summary description of the type of action in controlling the
valve.
Reset:
summary description of the type of reset following the activation
of the protector. Reset is controlled to avoid swings around the activation
threshold or immediate reactivation of the protector.
Note:
all alarms are generated after a fixed delay, as shown in the table:
Protectors
Delay (s)
LowSH
300
LOP
300
MOP
600
LowSH (low superheat)
The protector is activated so as to prevent the low superheat from
causing the return of liquid to the compressor.
Par. Description
Def. Min. Max.
U.M.
C1 LowSH protection: threshold
5(9) -5(-9) Set point
superheat
K(°F)
C2 LowSH protection: integration time
15
0
800
s
When the superheat value falls below the threshold, the system enters low
superheat status, and the intensity with which the valve is closed is increased:
the more the superheat falls below the threshold, the more intensely the
valve will close. The LowSH threshold must be less than or equal to the
superheat set point. The low superheat integration time indicates the
intensity of the action: the lower the value, the more intense the action.
The integration time is set automatically based on the type of main
control.
t
t
t
OFF
ON
A
OFF
ON
Low_SH
Low_SH_TH
SH
D
B
Fig. 6.a
key:
SH
Superheat
A
Alarm
Low_SH_TH Low_SH protection threshold
D
Alarm delay
Low_SH
Low_SH protection
t
Time
B
Alarm automatic reset