Siemens simatic c7-621 Hardware Installation Manual page 120

Safety of Electronic Controllers
The Risks Wherever injury to persons or damage to equipment can occur, special safety
requirements must be met in the system. With such applications, there are
special, system-specific regulations to be taken into account when designing
the control system (for example VDE 0116 for furnaces).
With safety-oriented electronic controllers, the measures necessary to avoid
or contain errors are based on the risk involved in the system. Where the
potential dangers in a system are higher, the basic measures listed above are
no longer adequate. Additional measures (for example redundancy, tests,
checksums etc.) must therefore be implemented and certified for the
controller (DIN VDE 0801). The fail-safe programmable controller S5-95F
was tested by the TÜV, BIA and G EM III and has several certificates. This
along with the fail-safe programmable controller S5-115F is suitable for
controlling and monitoring areas where safety is a prime consideration.
Division into In almost all systems and plants, there are components that are responsible
Safety and
for safety (for example emegency stop switches, protective screens, two-hand
Non-Safety Areas
switches). To avoid having to the view the entire control system from a safety
point of view, a control system is normally divided into a safety and a
non-safety area. In the non-safety area, there are no particular requirements
in terms of safety, since failure of the electronics does not affect the safety of
the plant or process. In the safety area, only controllers or circuits can be
used that meet the relevant safety regulations.
Areas are normally divided as follows:
1. For controls with few safety requirements (for example machine controls)
2. For controls with clearly delineated safety areas (for example chemical
3. For controllers where safety aspects are dominant (for example furnace
Important Note Even when the planning of an electronic control system achieves a high
degree of safety - for example with a multichannel configuration, the
instructions in the manuals must nevertheless be followed carefully. Incorrect
operation can lead to mechanisms intended to prevent serious situations
being put out of action or to unforeseen dangers.
C-2
The conventional programmable controller handles machine control
itself, parts where greater safety is required are controlled by the fail-safe
mini PLC S5-95F.
plants, cable cars)
The non-safety area is once again implemented using conventional
programmable controllers, the safety areas are controlled by tested
fail-safe controllers (S5-115F or several S5-95Fs).
The entire plant is implemented using a fail-safe control concept.
systems)
The entire control system is fail-safe.
C7-621 / C7-621 AS-i Control Systems
C79000-G7076-C621-01