The positioner safety function is declared as Type A element

with HFT=0 according to IEC 61508 capable to be used for SIL

Functional Safety Functions up to SIL 2.

According to IEC 61508-2. 7.4.7.4 a useful lifetime, based on

experience should be assumed.

The components of the positioner do not contain any specific

components with a reduced useful lifetime that are contributing

to the dangerous undetected failure rates.

Because the positioner is a moving masses system supplied by

instrumented air the final device usage and environmental

operating conditions (e.g., no/many open-close cycles,

good/bad supply air quality) will have an impact on the usefullifetime.

Therefore, the useful lifetime should be evaluated by the end

user according to the final plant experience data.

The Periodic Proof-Test methods within chapter Periodic Proof

Test and Maintenance on page 9 are suggested to validate the

correct safety function.

When final plant experience, proof testing and related field

monitoring data indicates a limiting useful lifetime by related

operating conditions, then the plant experience-based lifetime

must be used and considered on the failure rates, proof-test

intervals, and replacement intervals.