Safety and SIS · Glossary

What is Proof Test Coverage?

Symbol: PTC%Safety and SIS

Proof test coverage is the fraction of dangerous undetected failures that a proof test actually reveals.

Proof Test Coverage Explained

Real tests rarely find everything: a test that injects a signal at the transmitter does not test the sensor or tapping. Failures not covered stay hidden until replacement.

Low coverage raises PFDavg over the mission time, so imperfect tests must be accounted for.

Proof Test Coverage Formula

PFDavg ≈ PTC × λ_DU TI ÷ 2 + (1 − PTC) × λ_DU MT ÷ 2

PTC	proof test coverage
MT	mission time or replacement interval

Calculators for Proof Test Coverage

CalculatorProof Test Interval CalculatorFree online calculator with formula and worked example.CalculatorPFDavg CalculatorFree online calculator with formula and worked example.

Free Downloads

Free downloadSIL Proof Test Record Template in ExcelFree download in Excel and PDF.Free downloadESD Valve Proof Test ProcedureFree step by step procedure, Word and PDF.

Frequently Asked Questions

What is Proof Test Coverage?

Proof test coverage is the fraction of dangerous undetected failures that a proof test actually reveals.

How do I increase coverage?

Test from the process side: apply real pressure or level, stroke the valve fully and check tight shut off.

Where do PTC values come from?

From the device safety manual for a described test procedure.

Learn more on the blog

What is SIL (safety integrity level)

A practical guide on instrumentationblog.in with more detail on proof test coverage and how it is applied on real plants.

Read Full Article

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