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SIL / PL PFHd Estimator

Evaluate Probability of Dangerous Failure per Hour for a safety loop.

Subsystem PFHd

x 10^
x 10^
x 10^

Total System PFHd

0.00 1/h
ISO 13849-1
PL e
IEC 62061
SIL 3
info
Disclaimer of Liability: This calculator is provided for educational and estimation purposes only. By using this tool, you agree to discharge AutomationView of any liability for direct, indirect, or consequential damages resulting from its use. It is your strict responsibility to independently verify all calculations, validate the results against official manufacturer documentation, and ensure compliance with all applicable safety and engineering standards before implementing any parameters in a production environment.

Estimating Safety Integrity (SIL) and Performance Level (PL)

When designing safety-related parts of control systems (SRP/CS), engineers must evaluate the reliability of safety functions using international standards. The two primary standards are ISO 13849-1 (which defines Performance Level, PL) and IEC 62061 (which defines Safety Integrity Level, SIL).

The Role of PFHd

Both standards rely on the Probability of a dangerous failure per hour (PFHd) to quantify reliability. By calculating the PFHd of a complete safety loop (sensor, logic solver, and actuator), engineers can determine the resulting PL or SIL.

  • PL e / SIL 3: PFHd ≥ 10-8 to < 10-7
  • PL d / SIL 2: PFHd ≥ 10-7 to < 10-6
  • PL b, c / SIL 1: PFHd ≥ 10-6 to < 10-5

Key Variables for Estimation

To accurately estimate the PFHd, several variables must be considered for each subsystem:

  • MTTFd (Mean Time to Dangerous Failure): The expected time until a component fails dangerously.
  • DC (Diagnostic Coverage): The effectiveness of the system’s automatic diagnostics to detect dangerous failures.
  • CCF (Common Cause Failure): A score evaluating failures resulting from a single event.
  • Architecture (Category): The structure of the safety channel, ranging from Category B (single channel) to Category 4 (dual channel with high diagnostics).

Using an Estimator Tool

A SIL / PL PFHd estimator simplifies the complex mathematical modeling required by ISO 13849-1 and IEC 62061. By selecting the architecture category, MTTFd, and DC, automation engineers can rapidly verify if their proposed safety circuit meets the required risk reduction targets before utilizing advanced tools like SISTEMA.