Functional safety is a sub-area of the safety of a system. It refers to the correct functioning of the safety-related system and other risk-reducing measures.
Electrical safety, fire protection or radiation protection are therefore not part of functional safety. Alternatively, one often speaks of the safety integrity of the system, since safety can also be achieved by emergency shutdown and the assumption of a safe state. Functional safety is therefore possibly also given if the system no longer performs its intended function and is switched off.
With the complexity of electronic and especially programmable systems, the variety of possible errors increases: Microcontrollers now perform almost all safety functions.
They ensure, for example, that the temperature in a chemical production step remains constant; guide trains at an appropriate speed onto the right tracks or prevent airbags from being triggered at the wrong moment.
The various aspects of functional safety are defined in the IEC 61508 series of standards “Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems”. They range from concept, planning, development and implementation to commissioning, maintenance and modification, decommissioning and deinstallation. Among other things, the following methods for fault prevention are mentioned:
- Avoidance of systematic errors in development, e.g. specification and implementation errors
- Detection of random errors (e.g. ageing of components) by monitoring during operation
- Safe control of detected errors and transition to a previously defined safe state.
Important standards of functional safety
With regard to functional safety, the following standards are particularly relevant:
EN ISO 13849: Safety of machinery – Safety related parts of control systems
EN/IEC 61508: Functional safety of safety-related electrical/electronic/programmable electronic systems
EN/IEC 61511: Functional safety – Safety instrumented systems for process industries
EN/IEC 62061: Safety of machinery – Functional safety of safety-related electrical, electronic and programmable electronic control systems
ISO 26262: Functional safety for road vehicles
Standard series for motor vehicles: ISO 26262
An adaptation of this series of standards for motor vehicles is ISO 26262 (‘Functional safety of road vehicles’). It was published in November 2011 and has been legally binding since then.
An ever increasing number of electronic components and control units are installed in today’s cars. In addition, the networking of the individual components with each other is also increasing. As a result, the complexity of development is constantly increasing and is therefore subject to strict legal control in order to comply with the functional safety regulations. Current trends such as autonomous driving and the introduction of more and more digital assistance systems are fueling the need for functional safety more and more.
A simple example of functional safety in a car is the electronic stability program (ESP). The system looks at driving behavior and evaluates the risk of the car breaking away. If, for example, the car enters a curve too fast, an accident could occur and the system must therefore intervene because an accident is an intolerable risk. It may not be possible to prevent a skid completely, but ESP can limit the risk of an accident to an acceptable level.
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