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INNOVATIVE TECHNOLOGY

from sensor to the executive device, requirements of orders of Rostekhnadzor, etc.
When choosing a single supplier of EAP system tools, conceptual SRS should be a technical
requirement for the system as a whole. If it is not possible to choose a single supplier, then the
questionnaires for instrumentation and actuators, the technical requirements for the controller
are filled in taking into account SRS data.
The technical requirements for stage 2 should include the following requirements:
● Selection of circuit components, which is justified by the calculation of compliance with the
assigned SIL level. Circuit components with an assigned level of SIL1 and higher must be

certified and meet the requirements of GOST R
IEC 61508/61511.
● Verification of safety circuits taking into account
certain requirements for the designated SIL,
selected equipment and construction schemes
is carried out at the stage of creating working
Technical assignment documentation.
● Development of a detailed specification of SRS
safety requirements, taking into account the
selected equipment and the design decisions
made. The PAZ system provider, starting work on the second stage, based on the conceptual
specification of the SRS safety requirements, selects the elements of the protection circuits
from the sensor to the actuator and performs a verification calculation for compliance with the
assigned (target) SIL level.
When determining the conformity of the safety circuit to the assigned (target) SIL level,
the GOST R IEC 61508/61511 standard requires compliance with the requirements of three
standards:
1) safety integrity regarding systematic failures;
2) random failures;
3) architectural restrictions.
Mismatch to one of them entails a change in the intervals and testing methods, architecture,
or hardware implementation.
An example is the situation with shut-off valves. The SFF Safe Failure Rate will be less
than 60 %. According to the table. 2 GOST R IEC 61508-2, with an SFF of less than 60 %, two
cutoffs (HFT = 1) will need to be installed in the SIL2 circuit to ensure that three cutoffs will be
required in the SIL3 circuit (HFT = 2). When using testing, the partial stroke SFF will be more
than 90 %, and SIL3 will be enough for two shut-off valves (HFT = 1).

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