KROHNE TT 51 SERIES EN - Manual (Page 13)

SAFETY-RELATED CHARACTERISTICS
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TT 51 SERIES
www.krohne.com 09/2010 - 4000869801 - AD TT 51 SIL R01 en
Safety-related characteristics
7.1 Assumptions
The following assumptions have been made during the Failure Modes, Effects and Diagnostic
Analysis of the HART
® temperature transmitter TT 51 C&R SIL.
• Failure rates are constant, wear out mechanisms are not included.
• Propagation of failures is not relevant.
• External power failure rates are not included.
• The mean time to restoration (MTTR) after safe failure is 24 hours.
• For safety applications only the 4..20 mA output was considered. The HART ® protocol at
TT 51 C&R is only used for setup and diagnostic purpose, not during safety operation mode.
• The failure rates of the electronic components used in this analysis are obtained from a
collection of industrial databases.
• The temperature transmitters with 4..20 mA output are considered to be type B subsystems
with a hardware fault tolerance of 0.
• The failure rates do not include failures resulting from incorrect use of the equipment.
• The HART ® protocol is only used for setup, calibration and diagnostics purpose, not during
safety operation mode.
.book Page 13 Thursday, September 9, 2010 4:19 PM