IS & Ex


Functional safety with switches

February 2021 IS & Ex

Mechanical pressure and temperature switches perform sensitive tasks in safety relevant applications, e.g. monitoring limit values. Their functional safety must be guaranteed accordingly. This is always the case if the instruments fulfil the requirements of the corresponding safety integrity level (SIL) in accordance with the IEC 61508 standard.

WIKA switches have been issued SIL approval due to their proven operational reliability. Hazards to people, the environment and the plant that can emanate from critical processes must therefore be reduced to an acceptable minimum. IEC 61508 provides the necessary specifications for this. These are defined in different safety integrity levels, SIL 1 to 4.

The standard places equal responsibility on the responsible process developers and the manufacturers of the necessary components. For each instrument, it defines limit values for the probability of failure of a safety-relevant function. At the same time, it provides criteria for the possibility of controlling and avoiding systematic errors.

When the topic of ‘functional safety’ is discussed in expert groups in connection with SIL approval, it is mainly concerning electrical systems. However, numerous mechanical components are also integrated within safety-relevant applications. These include measuring instruments that do not need external power and therefore work reliably, even in the event of a power failure. A SIL approval for these also means a clear statement on functional safety. In the case of mechanical parts, it is primarily a question of the effects of ageing and wear.

The SIL certificate for WIKA’s pressure and temperature switches was issued in 2019 by exida, a globally recognised testing company. According to its assessment, the instruments, when installed individually, meet the requirements of SIL 2, and in redundant combination, they even meet those of the level SIL 3.


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