Emerson Rosemount 5300 Series - Terms and Definitions; Safety Instrumented System (SIS) Certification

8.2 Terms and definitions
Table 8-1: Terms and Definitions
Term Definition
DU Dangerous Undetected
FIT Failure In Time per billion hours
FMEDA Failure Modes, Effects and Diagnostic Analysis
HART
®
Highway Addressable Remote Transducer
HFT Hardware Fault Tolerance
PFD
AVG
Average Probability of Failure on Demand
SFF Safe Failure Fraction
SIF Safety Instrumented Function
SIL Safety Integrity Level – a discrete level (one out of four) for
specifying the safety integrity requirements of the safety
instrumented functions to be allocated to the safety
instrumented systems. SIL 4 has the highest level of safety
integrity, and SIL 1 has the lowest level.
SIS Safety Instrumented System – an instrumented system
used to implement one or more safety instrumented
functions. An SIS is composed of any combination of
sensors, logic solvers, and final elements.
Safety Response Time The delay between a change in the measured process and
the indication of that change at the safety-rated output.
Type B device Complex device using controllers or programmable logic,
as defined by the standard IEC 61508.
8.3 Safety Instrumented System (SIS) certification
For safety instrumented systems usage, the 4-20 mA analog output is used as the primary
safety variable. It is configured to activate the alarm function if an error occurs. If a
measured value goes beyond the measurement range, the transmitter enters saturation
mode (limit alarm is disabled) or alarm mode, depending on the current configuration.
The minimum time for the alarm condition is 200 ms.
The measurement signal used by the logic solver must be the analog 4-20 mA signal
proportional to the level generated. The HART protocol can only be used for setup,
calibration, and diagnostic purposes, not for safety critical operation.
The Rosemount 5300 Level Transmitter is IEC 61508 certified accordingly:
• Low and high demand: Type B element
• SIL 2 for random integrity @ HFT=0
• SIL 3 for random integrity @ HFT=1
• SIL 3 for systematic capability
Safety Instrumented Systems (4-20 mA only) Reference Manual
April 2019 00809-0100-4530
246 Rosemount 5300 Level Transmitter