AUMA SAV Series Manual

7. Safety-related figures
7.1. Determination of the safety-related figures
●
The calculation of the safety figures is based on the indicated safety functions.
Hardware assessments are based on Failure Modes, Effects and Diagnostic
Analysis (FMEDA). FMEDA is a step to assess functional device safety in
compliance with IEC 61508. On the basis of FMEDA, the failure rates and the
fraction of safe failures of a device are determined.
●
Experience data and data taken from the exida database for mechanical com-
ponents is used to calculate mechanical failure rates.The electronic failure
rates as base failure rates are taken from the SIEMENS Standard SN 29500.
●
In compliance with table 2 of IEC 61508-1, the average target PFD value for
systems with low demand mode are:
-
SIL 1 safety functions: ≥ 10
-2
to < 10
-1
-
SIL 2 safety functions: ≥ 10
-3
to < 10
-2
-
SIL 3 safety functions: ≥ 10
-4
to < 10
-3
Since actuators only represent a part of the overall safety function, the actuator
PFD value should not account for more than 25 % of the permissible total value
(PFD
avg
) of a safety function. This results in the following values:
-
Actuator PFD for SIL 1 applications: ≲ 2.50E-02
●
Safe end position feedback via end position switches directly wired via the
customer input can be classified as type A components with hardware fault
tolerance of 0.The SFF for the type A subsystem should be <60 % according
to table 2 of IEC 61508-2 for SIL 1 (subsystems with a hardware fault tolerance
of 0).The SFF for the type A subsystem should be between 60 % and <90 %
according to table 2 of IEC 61508-2 for SIL 2 (subsystems with a hardware fault
tolerance of 0).
●
The calculation of the PFD values is based on the following assumptions:
- MRT = 72 hours
- T
d
= 730 hours = time interval PVST
- MTTR = MRT + T
d
= 802 hours.
The PFD values specified in the declarations of incorporation and in this safety
manual are only examples and subject to certain assumptions e.g. on T
proof
, MTTR,
… The PFD calculation should always be performed individually for each system
using the parameters and conditions applicable for the respective system. The λ
DU
and λ
DD
values should be used as input.When observing the proof test procedures
indicated in this safety manual, we recommend calculation using proof test coverage
(PTC) of 90 %.
5)
.
As previously mentioned in the architecture section, safeguarding power supply and
resulting calculations are the responsibility of the plant operator.
The plant operator is responsible for eliminating faults within the MTTR, otherwise
the data of the quantitative results is no longer valid.
The safety figures mentioned in this safety manual and in the declarations of
incorporation are only valid if all the conditions stipulated in this safety
manual and in the declarations of incorporation and the mentioned activities
are respected. At the same time, the restrictions regarding the validity and
standard conformity stipulated in the declarations of incorporation must be
heeded.
5) For the example calculations within this manual and the declarations of incorporation, different PTC
values were sometimes used as calculation basis.
15
Multi-turn actuators
SA .2 with AC(V) 01.2/AC(V)ExC 01.2 Safety-related figures

AUMA SAV Series Specifications

General

Brand	AUMA
Model	SAV Series
Category	Controller
Language	English