Carel EVD Evolution Twin, Руководство пользователя

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ENG
“EVD Evolution TWIN” +0300006EN - rel. 2.6 - 31.01.2019 34
7. PROTECTORS
Note
: the HiTcond and reverse HiTcond protectors can be activated
if EVD Evolution twin works as a single driver (see Appendix 2) or if
programmable control is activated (see chap. on Control).
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.
7.1 Protectors
There are 3 protectors:
•
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;
•
integral 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 delay (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 affected by the proportional gain parameter (K) for the PID
superheat control. The higher the value of K, the more intense the reaction of
the protector will be.
C haracteristics of the protectors
Protection Reaction Reset
LowSH Intense closing Immediate
LOP Intense opening Immediate
MOP Moderate closing Controlled
Tab. 7.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.
Low S H (low superheat)
The protector is activated so as to prevent the return of liquid to the
compressor due to excessively low superheat values.
Parameter/description Def. Min. Max. UOM
CONTROL
LowSH protection: threshold
5 -40 (-72) SH set point K (°F)
LowSH protection: integral time 15 0 800 s
ALARM CONFIGURATION
Low superheat alarm delay
(LowSH) (0= alarm disabled)
300 0 18000 s
Tab. 7.b
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 integral time is set automatically based on the type of main control.
t
t
t
OFF
ON
A
OFF
ON
Lo w_ SH
Lo w_ SH _T H
SH
D
B
Fig. 7.a
Key:
SH Superheat A Alarm
Low_SH_TH Low_SH protection threshold D Alarm delay
Low_SH Low_SH protection t Time
B Automatic alarm reset
L OP (low evaporation pressure)
LOP= Low Operating Pressure
The LOP protection threshold is applied as a saturated evaporation
temperature value so that it can be easily compared against the technical
specifications supplied by the manufacturers of the compressors. The
protector is activated so as to prevent too low evaporation temperatures from
stopping the compressor due to the activation of the low pressure switch.
The protector is very useful in units with compressors on board (especially
multi-stage), where when starting or increasing capacity the evaporation
temperature tends to drop suddenly.
When the evaporation temperature falls below the low evaporation
temperature threshold, the system enters LOP status and is the intensity
with which the valve is opened is increased. The further the temperature falls
below the threshold, the more intensely the valve will open. The integral time
indicates the intensity of the action: the lower the value, the more intense
the action.
Parameter/description Def. Min. Max. UOM
CONTROL
LOP protection: threshold
-50 -60
(-76) MOP protection:
threshold °C (°F)
LOP protection: integral time 0 0 800 s
ALARM CONFIGURATION
Low evaporation temperature
alarm delay (LOP)
(0= alarm disabled)
300 0 18000 s
Tab. 7.c
The integral time is set automatically based on the type of main control.