Safety Of Electronic Control Equipment - Siemens SIMATIC S7-300 Hardware And Installation Manual

Appendix

12.4 Safety of electronic control equipment

Introduction
The notes below apply independent of the type or manufacturer of the electronic
control.
Reliability
Maximum reliability of SIMATIC devices and components is achieved by
implementing extensive and cost-effective measures during development and
manufacture:
This includes the following:
• Use of high-quality components;
• Worst-case design of all circuits;
• Systematic and computer-aided testing of all components;
• Burn-in of all large-scale integrated circuits (e.g. processors, memory, etc.);
• Measures preventing static charge when handling MOS ICs;
• Visual checks at different stages of manufacture;
• Continuous heat-run test at elevated ambient temperature over a period of
several days;
• Careful computer-controlled final testing;
• Statistical evaluation of all returned systems and components to enable the
immediate initiation of suitable corrective measures;
• Monitoring of major control components, using on-line tests (watchdog for the
CPU, etc.).
These measures are referred to in safety technology as basic measures. They
prevent or rectify a large proportion of possible faults.
Risks
In all cases where the occurrence of failures can result in material damage or injury
to persons, special measures must be taken to enhance the safety of the
installation - and therefore also of the situation. System-specific and special
regulations exist for such applications. They must be observed on installing the
control system (e.g. VDE 0116 for burner control systems).
For electronic control equipment with a safety function, the measures that have to
be taken to prevent or rectify faults are based on the risks involved in the
installation. As of a certain degree of hazard the basic measures mentioned above
are no longer sufficient. That is, additional measures (e.g. redundant
configurations, tests, checksums etc.) must be implemented and certified for the
control equipment (DIN VDE 0801). The prototype of the fail-safe PLC S5-95F was
tested by TÜV (German Institute for Technological Surveillance), BIA and G EM III;
several certificates have been granted. Thus, it is suitable in the same way as the
previously tested fail-safe PLC S5-115F to control and monitor safety-relevant
system areas.
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S7-300 Programmable Controller Hardware and Installation
A5E00105492-02