Terms And Definitions - Emerson Rosemount 5408 Reference Manual

Safety Instrumented Systems (SIS) requirements
February 2020
8.2

Terms and definitions

Table 8-1: Terms and Definitions
Term
BPCS
λ
DU
λ
DD
λ
SU
λ
SD
Diagnostic coverage
Diagnostic test interval
FIT
FMEDA
®
HART
HFT
High demand mode
Low demand mode
Mission time
PFD
AVG
Proof-test coverage factor
148
Definition
Basic Process Control System
Dangerous Undetected
Dangerous Detected
Safe Undetected
Safe Detected
Fraction of dangerous failures detected by automatic on-
line diagnostic tests.
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).
Failure In Time per billion hours
Failure Modes, Effects and Diagnostic Analysis
Highway Addressable Remote Transducer
Hardware Fault Tolerance
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).
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).
The time from an instrumented system's start-up until its
replacement or refurbishment to as-new condition.
Average Probability of Failure on Demand
The effectiveness of a proof-test is described using the
coverage factor which specifies the share of detected
dangerous undetected failures (λ
is an indication of a proof-test's effectiveness to detect
dangerous undetected faults.
Reference Manual
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). The coverage factor
DU
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