ABB LLT100, Functional Safety Manual

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Designing an SIF using the LLT100
15
Applications limits
The LLT100 can have flanges in aluminum or stainless steel. It is important for the designer to check
for material compatibility considering on-site chemical contaminants and air supply conditions. If the
LLT100 is used outside of the application limits or with incompatible materials, the reliability data
provided could become invalid.
The laser used for measuring distance is a class 1 laser (IEC60825-1 Ed 2, 2007).
Measuring laser safety
A class 1 laser is safe for all conditions of use.
Design verification
A Failure Mode, Effects and Diagnostics Analysis (FMEDA) summary report is available from ABB Inc.
This report details all the failure rates and failure modes as well as the expected lifetime of the LLT100.
The achieved SIL of an entire SIF design must be verified by the designer via a calculation of PFD
AVG
considering architecture, proof test interval, proof test effectiveness, any automatic diagnostics,
average repair time and the specific failure rates of all products included in the SIF. Each subsystem
must be checked to ensure compliance with minimum hardware fault tolerance requirements.
The safety parameters used for SIL calculation of the SIF are shown in “Safety parameters” below.
SIL capabilities
Systematic integrity
The product meets proven-in-use requirements for SIL 2. A SIF designed with this product must not be
used at a SIL level higher than the statement without prior-use justification by the end user or diverse
technology redundancy in the design.
Random integrity
The LLT100 is a type B device. Therefore, based on the SFF ≥ 90%, when the LLT100 is used as the only
component in a final element subassembly, a design can meet SIL 2 @ HFT=0. When the final element
assembly consists of many components, the SIL must be verified for the entire assembly using failure
rates from all components. This analysis must account for any hardware fault tolerance and architecture
constraints.
Safety parameters
The table below shows the failure rate information obtained from the FMEDA and other useful
information.
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Table 1
Characteristics as per IEC 61508
Parameter Value
Type of assessment proven in use
Safety Integrity Level 2