The requirements for a safety-related control system cannot be satisfied without additional measures, like those defined, for instance, in the Machinery Directive 2006/42/EC, in the European Standards EN ISO 13849-1 and EN ISO 13849-2. It has to be guaranteed that fault conditions can be controlled or will be detected with a very little residual error rate and ensuring to switch the machinery or system into a safe state in case of any failure.

The implementation of “safe control systems” requires certain connective concepts and principles in order to exclude fault assumptions. The fact that an individual device is declared to conform with certain Directives or EN standards will not guarantee the required suitability for the system network. Only the correct application of the individual hardware components and software modules will result in an efficient and safe overall system that is pieced together like a mosaic.

During practical seminars, it has been observed again and again that designers of control systems had not been familiar with the safety requirements for control systems and the validation process.

Knowledge and application of EN ISO 13849-1 and -2 are essential and the purpose of this brochure is to facilitate both. The 2014 edition has been editorially revised and expanded to include the key points in validation.

The structure of this leaflet is orientated to a “Step-by-Step” instruction aiming to present a possible way from “the development to the validation process” to designers and users of machinery building machines themselves or reconstructing machinery.

This leaflet however cannot replace studying EN ISO 13849-1 or EN ISO 13849-2. For reasons of handling and arrangement only those steps are dealt with that are significant for implementation and validation of safety-related control systems. Finally, the proposed way is illustrated and supplemented by a practical failure mode and effect analysis (FMEA).

Table of Contents

Introduction

1. Application of European Directives for safety-related control systems

Low voltage directive

EMC Directive

Machinery Directive

Harmonised standards for safety-related control systems – Overview – Characteristics of standard

2. Structure and application of EN ISO 13849-1

Performance level (PL)

Determination of the required performance level (PLr)

3. Basic parameter: Category

Category B

Category 1

Category 2

Category 3

Category 4

4. Determination of MTTF(d)

Procedure of determining MTTF(d)

MTTF(d) values for hydraulic components

MTTF(d) for pneumatic, mechanical and electromechanical components

5. Determination of Diagnostic Coverage DC(avg)

6. Common Cause Failures (CCF)

7. Compilation of parameters

8. PL for combinations of safety-related parts of a control system

9. Systematic failure

10. Software requirements

11. Software-based parameterization

12. Technical documentation

13. Instruction handbook

14. Validation

15. Example

Part 1: Estimation of the PL according to EN ISO 13849-1

Part 2: Validation according to EN ISO 13849-2

Terms and abbreviations

Formulary EN ISO13849-1

Bibliography

Index of Figures