SISTEMA Software for SRP/CS Evaluation and Verification

SISTEMA (Safety Integrity Software Tool for the Evaluation of Machine Applications) is a free software tool developed by the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA).

It is designed to assist engineers and safety professionals in evaluating the reliability and compliance of Safety-Related Parts of Control Systems (SRP/CS) in accordance with EN ISO 13849-1.

---

EN ISO 13849-1: A Comprehensive Overview

EN ISO 13849-1 is an international standard that specifies the principles for the design and evaluation of safety-related control systems used in machinery. It defines the required safety performance levels (PL) and provides methods to assess whether a control system meets these safety requirements.

Key Concepts of EN ISO 13849-1

1. Performance Level (PL)
   Performance Level (PL) is a key parameter in EN ISO 13849-1 that quantifies the reliability of a safety-related control function. It is divided into five levels:
   • PL a – Lowest level of reliability
   • PL b – Low reliability
   • PL c – Medium reliability
   • PL d – High reliability
   • PL e – Highest level of reliability
   The required PL (PLr) is determined based on the level of risk associated with a machine’s operation, taking into account the severity of injury, frequency of exposure, and possibility of avoiding the hazard.
2. Risk Assessment and PL Determination
   The standard uses a risk graph to determine the PLr based on:
   • Severity of injury (S): Minor (S1) or Serious (S2)
   • Frequency of exposure (F): Less frequent (F1) or Frequent/continuous (F2)
   • Possibility of avoiding the hazard (P): Possible (P1) or Almost impossible (P2)
   Based on this analysis, a required PLr is assigned, which the safety-related control system must achieve.
3. System Categories (Cat.)
   EN ISO 13849-1 defines five system categories (B, 1, 2, 3, and 4), which describe the architecture and fault tolerance of the control system:
   • Category B: Basic safety principles are applied, but there is no fault detection.
   • Category 1: Uses well-tried safety components but still lacks fault detection.
   • Category 2: Includes periodic testing of safety functions.
   • Category 3: Redundant architecture with fault detection, allowing continued safe operation even after a single fault.
   • Category 4: Full redundancy with fault detection and immediate action to prevent hazardous failure.
4. Reliability Parameters
   EN ISO 13849-1 also defines several reliability parameters to quantify the safety performance of SRP/CS:
   • Mean Time to Dangerous Failure (MTTFd): Estimated time before a dangerous failure occurs.
   • Diagnostic Coverage (DCavg): Effectiveness of fault detection.
   • Common Cause Failure (CCF): Probability of simultaneous failure of redundant components.
   These parameters are used in conjunction with system architecture to determine the achieved PL of a control system.

---

How SISTEMA Supports Compliance with EN ISO 13849-1

SISTEMA provides a structured framework for evaluating machine control systems against the requirements of EN ISO 13849-1. Its key features include:

1. Modelling of Safety-Related Parts of Control Systems (SRP/CS)
   SISTEMA allows engineers to create a hierarchical model of a machine’s safety-related control functions. This model reflects the architecture defined in EN ISO 13849-1, including input devices (e.g., sensors), logic controllers (e.g., PLCs), and output devices (e.g., actuators).
2. Performance Level Calculation
   The software automatically calculates the achieved Performance Level (PL) based on user-input parameters such as system category, MTTFd, DCavg, and CCF. Any changes to these values immediately update the PL calculation, helping engineers optimise their system design.
3. Component Libraries for Accurate Data
   Many manufacturers provide SISTEMA-compatible libraries containing preloaded reliability data for their safety components. This allows engineers to use accurate MTTFd and DC values directly in their calculations.
4. Common Cause Failure (CCF) Analysis
   SISTEMA includes built-in tools to assess CCF factors, ensuring that redundant systems are properly designed to avoid simultaneous failures due to environmental or design-related influences.
5. Detailed Reporting for Compliance Documentation
   The software generates comprehensive reports that document the safety evaluation process. These reports can be used to demonstrate compliance with EN ISO 13849-1 during audits and regulatory approvals.

---

Applications of SISTEMA in Machine Safety

SISTEMA is widely used in industries where functional safety is critical, such as:

• Manufacturing – Evaluating safety interlocks, emergency stop circuits, and light curtains.
• Robotics – Ensuring safety compliance for collaborative and automated robotic systems.
• Automotive – Assessing the safety of programmable electronic control systems.
• Packaging – Verifying safety mechanisms in automated conveyor and packaging systems.

---

System Requirements for SISTEMA

SISTEMA is compatible with:

• Operating Systems: Windows 7, Windows 10, and Windows 11.
• Minimum Requirements: 100 MB of free disk space, MS Internet Explorer 5.0 or higher, and a screen resolution of at least 1024 × 768 pixels.

---

Conclusion

SISTEMA is an essential tool for machine safety engineers, offering a structured, accurate, and efficient method for verifying compliance with EN ISO 13849-1. By enabling detailed risk assessments, performance level calculations, and documentation, it significantly reduces the complexity of safety system validation and ensures compliance with regulatory standards.