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Hans Turck GmbH & Co. KG | T +49 208 4952-0 | F +49 208 4952-264 | [email protected] | www.turck.com
Safety Planning
5
Safety Planning
This chapter provides information for planning a safety-related loop.
The device is not specified for a certain application. Make sure that the data provided in this
chapter is valid for your target application.
Special application-specific factors may cause the premature wear of the device and must be
taken into consideration when planning systems; take special measures to compensate for a
lack of experience based values, e.g. through implementation of shorter test intervals.
The suitability for specific applications must be assessed by considering the particular overall
safety-related system with regard to the requirements of IEC 61508.
Safety-planning must only be carried out by trained and qualified personnel.
If there is any doubt contact Turck directly.
5.1
Architectural specifications
Due to architectural considerations the following characteristics are specified:
Type
B
HFT
0
Experience has shown that the useful lifetime often lies within a range of 8 to 12 years. It can
be significantly less if elements are operated near their specification limits. However, it can
be extended by appropriate measures. For example, heavy temperature fluctuations could
potentially decrease the useful lifetime, as constant temperature below 40 °C could potentially
increase the useful lifetime.
The relay [A1D] must be protected against an over current (cos phi = 1, I = 2 A AC).
For the relay outputs the useful lifetime is 8 to 12 years or 30.000 switching cycles.
5.2
Assumptions
■
Failure rates are constant for 10 years, wear out mechanisms are not included
■
Propagation of failures are not relevant
■
External power supply failure rates are not included
■
All components that are not part of the safety function and cannot influence the safety func-
tion (feedback immune) are excluded.
■
Only one input and one output are part of the safety function