SISTEMA Report Guide: ISO 13849-1 PL Calculation & Machine Safety
Machine safety is a critical aspect of modern manufacturing. As global regulations tighten, equipment builders must prove their machines meet stringent safety standards. The SISTEMA report, developed by the German Institute for Occupational Safety and Health (IFA), has become the gold standard for evaluating safety-related control systems. This article explains what a SISTEMA report is, how it works, and why it is essential for CE marking and international market access.
What Is a SISTEMA Report?
SISTEMA stands for Safety Integrity Software Tool for the Evaluation of Machine Applications. It is a free software tool provided by IFA that automates the calculation of the Performance Level (PL) according to ISO 13849-1. The report generated by SISTEMA documents the safety function design, component data, and the achieved PL or Safety Integrity Level (SIL). It serves as proof that a machine’s safety-related control system meets the required risk reduction level.
For machinery exported to Europe, a SISTEMA report is often mandatory to demonstrate compliance with the Machinery Directive 2006/42/EC. Without it, machines may be denied entry, face costly recalls, or expose manufacturers to legal liability.
Key Components of a SISTEMA Report
A thorough SISTEMA report includes several critical elements:
- Safety Function Identification: Each safety function (e.g., emergency stop, light curtain, guard interlock) is clearly defined with its required PLr (required Performance Level).
- Architecture Analysis: The control system architecture is categorized (Category B, 1, 2, 3, or 4) based on redundancy and monitoring.
- Component Data: For each component (sensor, logic, actuator), parameters like MTTFd (Mean Time to Dangerous Failure), DC (Diagnostic Coverage), and CCF (Common Cause Failure) score are entered.
- PL Calculation: The software calculates the achieved PL (a, b, c, d, or e) and compares it with the required PLr.
- Verification and Validation: The report confirms that the design meets the standard and that the safety functions are correctly implemented.
| Parameter | Description | Typical Values |
|---|---|---|
| MTTFd | Mean Time to Dangerous Failure per channel | Low: 3-10 years, Medium: 10-30 years, High: 30-100 years |
| DC | Diagnostic Coverage (effectiveness of fault detection) | None: <60%, Low: 60-90%, Medium: 90-99%, High: ≥99% |
| CCF Score | Common Cause Failure mitigation measures | Minimum 65 points required for Cat. 2-4 |
| PL | Performance Level (probability of dangerous failure per hour) | a: ≥10⁻⁵ to <10⁻⁴, b: ≥3×10⁻⁶ to <10⁻⁵, c: ≥10⁻⁶ to <3×10⁻⁶, d: ≥10⁻⁷ to <10⁻⁶, e: ≥10⁻⁸ to <10⁻⁷ |
How to Generate a Valid SISTEMA Report
Creating a compliant SISTEMA report requires a systematic approach:
- Risk Assessment: Perform a risk assessment according to ISO 12100 to determine the required PLr for each safety function.
- Safety Concept Design: Define the safety functions and select components (e.g., safety relays, contactors, drives) with known safety parameters.
- Data Collection: Gather MTTFd, DC, and other data from component manufacturers’ certificates (e.g., TÜV, UL).
- SISTEMA Project Setup: Enter the safety functions, architecture, and component data into the SISTEMA software.
- Calculation and Verification: Run the calculation and verify that PL ≥ PLr. Adjust design if necessary.
- Documentation: Generate the report and include it in the technical file for CE marking.
Common Challenges and Solutions
Many machine builders face difficulties when preparing SISTEMA reports:
- Incomplete Component Data: Some components lack certified safety parameters. Solution: Use components from reputable manufacturers that provide functional safety data (e.g., Siemens, Rockwell Automation, Omron).
- Incorrect Architecture Selection: Misunderstanding of categories can lead to under- or over-engineering. Solution: Consult ISO 13849-1 Annex B for guidance.
- CCF Score Below 65: This is a common pitfall. Solution: Implement measures like separation of channels, overvoltage protection, and regular testing.
- Software Errors: Manual calculation errors are eliminated by using SISTEMA, but incorrect data entry can still occur. Solution: Double-check all inputs and use the built-in plausibility checks.
Real-World Application: Industrial Robot Cell
Consider a robotic welding cell. The safety functions might include:
- Emergency stop (PLr = d)
- Light curtain for area protection (PLr = d)
- Guard door interlocking (PLr = c)
Using SISTEMA, the designer can model each safety function. For the emergency stop, a dual-channel architecture (Cat. 3) with a safety relay having MTTFd = 100 years and DC = 99% might achieve PL e. The report documents this, providing evidence for the technical file. Without such a report, the robot cell cannot be CE marked, blocking its entry into the European market.
Benefits Beyond Compliance
A SISTEMA report is not just a bureaucratic requirement. It offers tangible benefits:
- Enhanced Safety: The systematic analysis reduces the risk of accidents, protecting operators and equipment.
- Competitive Advantage: Machines with documented safety performance are more attractive to safety-conscious buyers.
- Reduced Liability: In case of an incident, the report demonstrates due diligence.
- Design Optimization: The process often reveals opportunities to simplify the safety system without compromising safety.
Integrating SISTEMA with Other Standards
While SISTEMA focuses on ISO 13849-1, it can also be used for SIL verification under IEC 62061. The software includes a SIL/PL comparison table. For complex systems, combining SISTEMA with other tools like PAScal or Sistema-based libraries from component manufacturers streamlines the process. Many industrial automation companies now provide SISTEMA libraries for their safety products, making it easier to build accurate models.
Conclusion
The SISTEMA report is an indispensable tool for machine safety compliance. It translates complex safety calculations into a clear, auditable document. For machine builders aiming for global markets, investing in proper safety design and documentation is not optional—it is a business necessity. By mastering SISTEMA, engineers can ensure their machines are both safe and competitive.
Whether you are designing a simple electrical control panel or a complex automated production line, the principles of functional safety remain the same. A well-executed SISTEMA report is your proof that safety has been engineered into the system from the start.
