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

Reference Manual
00809-0100-4408
Table 8-1: Terms and Definitions
Term
Safety deviation
SFF
SIF
SIL
SIS
Systematic Capability
Transmitter response time
Type B device
Useful lifetime
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
Rosemount 5408 and 5408:SIS Level Transmitters
(continued)
Definition
The maximum allowed deflection of the safety output due
to a failure within the device (expressed as a percentage of
span).
Any failure causing the device output to change less than
the Safety Deviation is considered as a "No Effect" failure.
All failures causing the device output to change more than
the Safety Deviation and with the device output still within
the active range (non-alarm state) are considered
dangerous failures.
Note that the Safety Deviation is independent of the
normal performance specification or any additional
application specific measurement error.
Safe Failure Fraction
Safety Instrumented Function
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.
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.
Systematic Capability is a measure (expressed on a scale of
SC 1 to SC 4) of the confidence that the 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 instructions specified in the compliant item safety
manual for the element.
The time from a step change in the process until
transmitter output reaches 90% of its final steady state
value (step response time as per IEC 61298-2).
Complex device using controllers or programmable logic,
as defined by the standard IEC 61508.
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, warranty, or other
commercial issues.
Safety Instrumented Systems (SIS) requirements
February 2020
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