June 2021
Installation, Operation and Maintenance Manual
MAN712 Rev. 9
Section 5: Working Principle and Detailed Description
Working Principle and Detailed Description
24
5.1.2.6
Safety Action Delay
The ELBS-20 is fitted with a configurable time delay module that allows delaying the
starting of the Safety Action. The Delay is expressed in number of Samples. The time
between two consecutive samples is determined by the set “S.Rate” (see Section 6).
Example: “Delay” = 2 samples, “S.Rate” = 8 seconds => the Safety action is delayed of
16 seconds (2*8).
If the condition which causes the event (low pressure EVENT 2, high pressure EVENT 4,
pressure drop rate EVENT 6), disappears during the delay time, the Safety Action will
not start.
The “Delay” parameter has no effect on Safety Action caused by the Digital Input
Command and the Simulation Test (Safety Action).
5.1.2.7
Execution of the Safety Action
The Safety Action is performed in the following way: the ELBS-20 controls the selected
SOV Control Outputs for commanding the actuator to stroke the line valve to the
fail-safe position.
The ELBS-20 initiates the Safety Action if the Operating Mode is VC or VC+ACQ
(see Section 5.1.1), no alarms are active and one of the following conditions is satisfied:
•
EVENT 2 happens (see Section 5.1.2.2)
•
EVENT 4 happens (see Section 5.1.2.2)
•
EVENT 6 happens (see Section 5.1.2.1) (*)
•
Digital Input command (see Section 5.1.2.5)
•
“Start Test Safety Action” command (see
Section 6 and Section 5.1.2.4)
•
Pressure Drop Simulation Test (see Section 6 and Section 5.1.2.3) (**)
In case of EVENT 2, 4 and 6 the Safety action starts after the set value of the “Delay”
parameter (see Section 5.1.2.6).
It is possible to select several SOV Control Outputs for initiating the Safety Action
(see Section 5.2.8).
The ELBS-20, for performing the Safety Action, commands the dedicated SOV Control
Outputs SVC1, SVC2, RL1 and RL2 for a time settable through the “Duration” parameter.
If DO1 and DO2 Digital Outputs are used as SOV Control Outputs (see Section 6.2),
the “Duration” parameter has no effect on them. DO1 and DO2 commute for initiating
the Safety Action and it is necessary to set the ELBS-20 in VC or VC+ACQ Operating Mode
to restore their initial status (see Section 11).
