Safety Instrumented System (Sis) Certification - Emerson Rosemount 5408 Reference Manual

Table 8-1: Terms and Definitions
Term Definition
Systematic Ca- Systematic Capability is a measure (expressed on a scale of SC 1 to SC 4) of the confidence that the
pability systematic safety integrity of an element meets the requirements of the specified SIL, in respect of
the specified element safety function, when the element is applied in accordance with the instruc-
tions specified in the compliant item safety manual for the element.
Transmitter re- The time from a step change in the process until transmitter output reaches 90% of its final steady
sponse time state value (step response time as per IEC 61298-2).
Type B device Complex device using controllers or programmable logic, as defined by the standard IEC 61508.
Useful lifetime Useful lifetime is a reliability engineering term that describes the operational time interval where the
failure rate of a device is relatively constant. It is not a term which covers product obsolescence, war-
ranty, or other commercial issues.
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.
The measurement signal used by the logic solver must be the analog 4-20 mA signal
proportional to the level or distance (ullage) generated. The HART protocol can only be
used for setup, calibration, and diagnostic purposes, not for safety critical operation.
The Rosemount
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Rosemount 5408 and 5408:SIS Level Transmitters
(continued)
™
5408:SIS 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)
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