Ashcroft A Series - N4 Pressure Switch - Manual (Page 6)

A-S ERIES S WITCH S AFETY M ANUAL
I&M009-10210
REV A - 4/19/2013
The product has met manufacturer design process requirements of Safety Integrity
Level (SIL) 3. These are intended to achieve sufficient integrity against systematic
errors of design by the manufacturer. A Safety Instrumented Function (SIF)
designed with this product must not be used at a SIL level higher than the
statement without “prior use” justification by end user or diverse technology
redundancy in the design.
3.5.2 Random Integrity
The A-Series pressure switch is a Type A Device. Therefore based on the SFF
between 60% and 90%, when the A-Series pressure switch is used in low trip
applications, and as the only component in a final element subassembly, a design
can meet SIL 2 @ HFT=0. When used in high trip applications the SFF is <60%;
therefore the architectural constraints are SIL 1 @ HFT=0 & SIL 2 @ HFT=1.
When the 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.
3.5.3 Safety Parameters
For detailed failure rate information refer to the Failure Modes, Effects and
Diagnostic Analysis Report for the A-Series pressure switch.
3.6 General Requirements
The system’s response time shall be less than process safety time. The A-Series
pressure switch will change state in less than 1 S under specified conditions.
All SIS components including the A-Series pressure switch must be operational
before process start-up.
User shall verify that the A-Series pressure switch is suitable for use in safety
applications by confirming the A-Series pressure switch’s nameplate is properly
marked.
Personnel performing maintenance and testing on the A-Series pressure switch
shall be competent to do so.
Results from the proof tests shall be recorded and reviewed periodically.
The useful life of the A-Series pressure switch is discussed in the Failure Modes,
Effects and Diagnostic Analysis Report for the A-Series pressure switch.