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Verify PFDavg against IEC 61511 SIL requirements for any SIS architecture. Enter your details to unlock — no spam, ever.

1oo1, 1oo2, 2oo2, 2oo3 architectures

PFDavg per IEC 61511

Common cause factor (β)

Diagnostic coverage (DC)

SIL achieved vs. required

Architecture comparison table

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SIL
Verification Tool

Calculate PFDavg for your Safety Instrumented System and verify whether it meets the required Safety Integrity Level per IEC 61511. Supports 1oo1, 1oo2, 2oo2, 2oo3, and 1oo2D architectures with common cause and diagnostic coverage.

IEC 61511 / ISA-84 1oo1 / 1oo2 / 2oo2 / 2oo3 Common Cause (β) Diagnostic Coverage (DC) Architecture Comparison Print Report

IEC 61511 SIL PFDavg Ranges

SIL 10.01 – 0.1

SIL 20.001 – 0.01

SIL 30.0001 – 0.001

SIL 4< 0.0001

PFDavg = λ_DU × TI/2 (1oo1)simplified

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Safety Instrumented Function

Describe the SIF being verified

SIF Description

Required SIL

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SIS Architecture

Voting configuration for sensors, logic solver, and final elements

Voting Architecture (applies to each subsystem independently)

1oo1

Single channel. Simplest, lowest cost — but highest PFD for a given λ.

1oo2

Dual redundant. Either channel can trip. Lower PFD, higher spurious trip rate.

2oo2

Both channels must agree to trip. Lower spurious trips, higher PFD than 1oo2.

2oo3

Triple redundant, 2-of-3 majority vote. Balances reliability and availability.

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Failure Rate Parameters

Per IEC 61508 / SIL Tier 2 assessment data

Total Dangerous Failure Rate (λ_D) /hr

Typical values: transmitter 1×10⁻⁶/hr, valve 2×10⁻⁶/hr, logic solver 1×10⁻⁷/hr. Source from SIL Tier 2 assessment or EXIDA/SIS-TECH data.

Diagnostic Coverage (DC) 0–1

DC = fraction of dangerous failures detected by online diagnostics. Drives the split between λ_DD (detected) and λ_DU (undetected).

Proof Test Interval (TI) years

Common Cause Factor (β) for redundant architectures

β is the fraction of failures that affect all redundant channels simultaneously. Ignored for 1oo1 — only applies to 1oo2, 2oo2, 2oo3.

Mission Time (T_M) years — typically 20 years per IEC 61511

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Architecture Comparison

PFDavg for all architectures with current failure rate parameters

Architecture	PFDavg	SIL Achieved	Status vs. SIL 2

SIL Verification Result

New SIF

Calculated PFDavg

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Enter parameters above

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AWAITING INPUT

Enter λD and proof test interval to verify

Required SIL

SIL 2

PFDavg 0.001–0.01

SIL Achieved

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Calculation Breakdown

Enter parameters to see calculation—

Architecture 1oo1

λDU (undetected dangerous) —

Proof Test Interval —

📚 IEC 61511 Reference — Failure Rate Data & PFD Formulas

Typical Dangerous Failure Rates (λD)

Component	λD (/hr)
Pressure transmitter	1×10⁻⁶
Temperature transmitter	5×10⁻⁷
Level transmitter	2×10⁻⁶
Flow transmitter	1×10⁻⁶
Pressure switch	3×10⁻⁶
Solenoid valve	5×10⁻⁷
Control valve (SIL-rated)	2×10⁻⁶
Logic solver / PLC (SIL-rated)	1×10⁻⁷
Relay (safety rated)	1×10⁻⁷

PFDavg Formulas Used (IEC 61508-6)

Architecture	Simplified PFDavg Formula
1oo1	λDU × TI/2
1oo2	(1−β)(λDU·TI)²/3 + β·λDU·TI/2
2oo2	λDU × TI
2oo3	(1−β)(λDU·TI)² + β·λDU·TI/2

Where λDU = λD × (1 − DC). TI = proof test interval in years. β = common cause factor. Formulas are simplified per IEC 61508-6 Annex B — for full SIL Tier 3 verification use Markov or fault tree analysis.

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