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Environmental Limits
The designer of a SIF must check that the product is rated for use within the expected environ-
mental limits as stated in Table 10 on page 73.
Application limits
Application limits for the SVI II ESD installed in a SIF include:
Design Verification
The design verification criteria for the SIF and the SVI II ESD include:
SIL Capability
The SVI II ESD meets SIL 3 requirements as outlined below.
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The application of the SVI II ESD is limited for SIF where the safe state is the
de-energized state (shutdown) of the valve. The PST Controller may be
operated with either one of two control signals: 4 - 20 mA or 0 - 24 VDC.
With a 4 - 20 mA control signal, normal operation is with a 20 mA current
loop signal to the PST controller. A shutdown command is issued by taking
the current to 5.6 mA or lower.
With a 0 - 24 VDC control signal, normal operation is with a 24 VDC signal
applied to the PST controller. A shutdown command is issued by interrupting
the loop or taking the voltage signal to 3 VDC or lower.
A detailed Failure Mode, Effects, and Diagnostics Analysis (FMEDA) report is
available from the factory. This report details all failure rates and failure
modes as well as the expected lifetime.
The achieved Safety Integrity Level (SIL) of an entire Safety Instrumented
Function (SIF) design must be verified by the designer via a calculation of
PFDavg considering redundant architectures, 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 assure compliance with minimum hardware fault tolerance
(HFT) requirements. The exida exSILentia
purpose as it contains accurate models for the SVI II ESD and its failure rates.
When using an SVI II ESD in a redundant configuration, include a common
cause factor of 5% in safety integrity calculations.
The failure rate data listed in the FMEDA report is only valid for the useful life
time of an SVI II ESD. The failure rates increase sometime after this time
period. Reliability calculations based on the data listed in the FMEDA report
for mission times beyond the lifetime may yield results that are too
optimistic, i.e. the calculated Safety Integrity Level will not be achieved.
*
tool is recommended for this
Masoneilan SVI II ESD Quick Start Guide =| 15
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