Siemens sipart PS2 Betriebsanleitung Seite 229

The assessment
used as a single-acting
the allowed range for SIL 2 according to table 2 of IEC 61508-1 and table 3.1 of ANSI/ISA–
84.01–1996 and a Safe Failure Fraction (SFF) of more than 84%. Based on the verification
of "proven-in-use"
IEC 61511-1
IEC 61511-1 First Edition 2003-01.
The failure rates listed above do not include failures resulting from incorrect use of the Electro-
pneumatic Positioner SIPART PS2, in particular humidity entering through incompletely closed
housings or inadequate cable feeding through the inlets.
The listed failure rates are valid for operating stress conditions typical of an industrial field
environment similar to IEC 60654-1 class Dx (outdoor location) with an average temperature
over a long period of time of 40ºC. For a higher average temperature of 60°C, the failure rates
should be multiplied with an experience based factor of 2,5. A similar multiplier should be used
if frequent temperature fluctuation must be assumed.
A user of the Electro-pneumatic Positioner SIPART PS2 can utilize these failure rates in a
probabilistic model of a safety instrumented function (SIF) to determine suitability in part for
safety instrumented system (SIS) usage in a particular safety integrity level (SIL). A full table of
failure rates for different operating conditions is presented in section 5.2 to 5.5 along with all
assumptions.
It is important to realize that the "no effect" failures and the "annunciation" failures are included
in the "safe undetected" failure category according to IEC 61508. Note that these failures on its
own will not affect system reliability or safety, and should not be included in spurious trip
calculations.
© exida.com GmbH
Stephan Aschenbrenner
SIPART PS2 mit und ohne HART-Kommunikation
Betriebsanleitung, 09/2008, A5E00074630-08
has shown that the Electro-pneumatic
shut-down module ("tight closing bottom") has a PF D
according to IEC 61508
it can be used as a single device for SIL2 Safety Functions
Positioner
and its direct relationship
siemens 04-12-06 r004 v1 r1.0.doc, April 11, 2005
A.3 Prüfbericht (Auszug)
SIPART PS2 when
within
AV G
to "prior-use" of
in terms of
Page 4 of 4
Anhang
231