© exida.com GmbH TURCK 04-07-14 R001 V2R0.doc; February 8, 2013
Stephan Aschenbrenner Page 4 of 4
The two channels on a redundant board shall not be used to increase the hardware fault
tolerance needed for a higher SIL as they contain common components.
A user of the Isolating Transducers IM33-**(Ex)-Hi/24VDC and Analog Signal Transmitters
IM35-**Ex-Hi/24VDC 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 is presented in
sections 5.1 and 5.2 along with all assumptions.
The failure rates are valid for the useful life of the Isolating Transducers
IM33-**(Ex)-Hi/24VDC and Analog Signal Transmitters IM35-**Ex-Hi/24VDC, which is
estimated to be between 8 and 12 years (see Appendix 2).
It is important to realize that the “no effect” 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.
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