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Reference Manual
00809-0100-4530, Rev DD
Safety Instrumented Systems (4-20 mA only)
May 2016
Safety Instrumented Systems (4-20 mA only)
8.2
Terms and definitions
DU:
Dangerous Undetected
FMEDA:
Failure Modes, Effects and Diagnostic Analysis
HART
®
:
Highway Addressable Remote Transducer
HFT:
Hardware Fault Tolerance
PFD
AVG
:
Average Probability of Failure on Demand
Safety Response Time:
The delay between a change in the measured process and the
indication of that change at the safety-rated output.
SIF:
Safety Instrumented Function
SIL:
Safety Integrity Level, discrete level (one out of a possible four) for specifying the safety
integrity requirements of the safety functions to be allocated to the E/E/PE safety-related
systems, where Safety Integrity Level 4 has the highest level of safety integrity, and Safety
Integrity Level 1 has the lowest.
SIS:
Safety Instrumented System – Implementation of one or more Safety Instrumented
Functions. A SIS is composed of any combination of sensor(s), logic solver(s), and final
element(s).
SFF:
Safe Failure Fraction
Type B device:
Complex device (using microcontrollers or programmable logic)
Any substitution of non-authorized parts or repair, other than exchanging the
complete transmitter head or probe assembly, may jeopardize safety and is
prohibited.
Unauthorized changes to the product are strictly prohibited as they may
unintentionally and unpredictably alter performance and jeopardize safety.
Unauthorized changes that interfere with the integrity of the welds or flanges,
such as making additional perforations, compromise product integrity and safety.
Equipment ratings and certifications are no longer valid on any products that have
been damaged or modified without the prior written permission of Emerson
™
Process Management. Any continued use of product that has been damaged or
modified without prior written authorization is at the customer's sole risk and
expense.