Siemens S7-400 Safety of Electronic Control Equipment, Intoduction Reliability, Risks

Assembling and Installing Systems

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 SIMATIC devices and components is achieved by implementing extensive and cost-effective measures during development and manufacture:

•Use of high-quality components;

•Worst-case design of all circuits;

•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 different stages 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 0116 for 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 Technological Suirveillance), BIA and G EM III; several certificates have been granted. These are suitable therefore for controlling and monitoring safety-relevant applications.

A-32	Automation System S7-400	Hardware and Installation
		A5E00850741-01