Emerson Rosemount 5408, Reference Manual

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8.2 Terms and definitions
Table 8-1: Terms and Definitions
Term Definition
BPCS Basic Process Control System
λ
DU
Dangerous Undetected
λ
DD
Dangerous Detected
λ
SU
Safe Undetected
λ
SD
Safe Detected
Diagnostic coverage Fraction of dangerous failures detected by automatic on-
line diagnostic tests.
Diagnostic test interval The time from when a dangerous failure/condition occurs
until the device has set the safety related output in a safe
state (total time required for fault detection and fault
reaction).
FIT Failure In Time per billion hours
FMEDA Failure Modes, Effects and Diagnostic Analysis
HART
®
Highway Addressable Remote Transducer
HFT Hardware Fault Tolerance
High demand mode The safety function is only performed on demand, in order
to transfer the EUC (Equipment Under Control) into a
specified safe state, and where the frequency of demands
is greater than one per year (IEC 61508-4).
Low demand mode The safety function is only performed on demand, in order
to transfer the EUC into a specified safe state, and where
the frequency of demands is no greater than one per year
(IEC 61508-4).
Mission time The time from an instrumented system’s start-up until its
replacement or refurbishment to as-new condition.
PFD
AVG
Average Probability of Failure on Demand
Proof-test coverage factor The effectiveness of a proof-test is described using the
coverage factor which specifies the share of detected
dangerous undetected failures (
λ
DU
). The coverage factor
is an indication of a proof-test’s effectiveness to detect
dangerous undetected faults.
Safety Instrumented Systems (SIS) requirements Reference Manual
February 2020 00809-0100-4408
148 Reference Manual