Assembling and Installing Systems
A-32 AutomationSystem S7-400 Hardwareand Installation
A5E00850741-01
A.11 Safety of Electronic Control Equipment

Intoduction

The notes below apply independent of the type or manufacturer of the electronic
control.

Reliability

Maximum reliability of SIMATICdevices and components is achieved by
implementing extensive and cost-effective measures during development and
manufacture:
•Use of high-quality components;
•Worst-case design of allcircuits;
•Systematic and computer-aided testing of all components;
•Birm-in of all large-scale integrated circuits (e.g. processors, memory,etc.);
•Measures preventing static charge when handling MOS ICs;
•Visual checks at differentstages of manufacture;
•Continuous heat-run test at elevated ambient temperature ove 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 compoments, 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

A higher degree of safety standard applies to all applications and situations where
there is a risk of material damage or injury upon the event of a failure. Special
system-specific regulations are applied to such applications and must be observed
on installing the control system (e.g. VDEE 0116for burner control systems).
For electronic control equipment with a safety function, the measures that have to
be taken to avoid or correct 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 S7-400F and S7-400FH PLCs were
tested by TÜV (German Institute for TechnologicalSuirveillance), BIA and G EM III;
several certificates have been granted. These are suitable therefore for controlling
and monitoring safety-relevant applications.