Emerson EL-O-Matic F Series - 4.5 Actuator to Valve Installation

16
SIL Safety Manual
DOC.SILM.EF.EN Rev. 1 September 2018
Architectural Constraints
Section 9: Architectural Constraints
For the evaluation of the conformity to the requirement of Hardware safety integrity
architectural constraints of the standard IEC 61508, both Route 1
H
and Route 2
H
are used.
Route 1
H
• The product has a single channel conguration, HFT (hardware fault tolerance)=0
• Safe failure rate λ
S
:
– Single Acting Actuators: According to IEC 65108 denitions (in particular
denitions 3.6.8 and 3.6.13 of IEC 61508-4), no Safe Failures are possible
in a Single Acting actuator. Each failure mode of the actuator itself shall be
classied as “Dangerous” or “No Effect” (failures which can generate the
spurious operation of the safety function are only external to the actuator
itself, or are related to components that “plays no part in implementing
the safety function”, e.g. components of the pneumatic cylinder.
Therefore, according to denition 3.6.13 of IEC 61508- 4, they cannot be
used for the calculation of the SFF.
Hence λ
S
=0 for each type of single acting actuator.
– Double Acting Actuators: According to IEC 65108 denitions (in particular
denitions 3.6.8 and 3.6.13 of IEC 61508-4), no Safe Failures are possible
in a Double Acting actuator. Each failure mode of the actuator itself shall
be classied as “Dangerous” or “No Effect” (failures which can generate
the spurious operation of the safety function are only external to the
actuator itself, and in the case of loss of power supply the actuator “stays
put”). Therefore, according to denition 3.6.13 of IEC 61508- 4, they
cannot be used for the calculation of the SFF.
Hence λ
S
=0 for each type of Double Acting actuator.
For this reason, according to denition 3.6.15 of IEC 61508-4, we have:
• SFF=0 without external diagnostic tests;
• SFF>0 with external diagnostic tests, carried out according to denition 3.8.7 of IEC
61508-4, and according to what written in Section 6 above
(see the same paragraph for the SFF / DC reachable).
Route 2
H
• The application of Route 2
H
(“eld feedback”) is assessed.
• As the product is classied as “Type A”, no requirements for SFF are
given for Route 2
H
.
In conclusion:
The product can be used in single channel conguration up to:
• SIL 2 without external diagnostic tests
• SIL 3 considering external diagnostic tests
Section 9: Architectural Contraints