HB-37420-810-01-25F-EN SMX100 Installation manual.docx Page 242 of 260
Version: 25F
12.3.4 Hardware specification
The hardware specification should describe the entire system design and, in particular, the
components used with their specific characteristic data. The hardware specification serves as
basis for the determination of the achieved safety level based on the architecture and the
characteristic data of all devices involved in a safety function.
Furthermore, the hardware specification should also specify the design measures applied for
protecting against systematic and common cause faults.
12.3.4.1 Selection of SRP/CS and operating means
The selection of SRP/CS (Safety related parts of control system) is most suitable to achieve
the intended safety level and should be made for any safety function. The components with
safety relevant function must be designated in a total overview of the system structure and are
to be assigned to the individual safety functions The safety related code numbers must be
determined for these components.
The code numbers cover the following values:
MTTFd = mean time to failure, the mean time until a danger imposing failure)
DC avg = Mean diagnostic coverage
CCF = common cause failure, a failure caused on a common cause
For an SRP/CS both the software and systematic faults must be taken into consideration.
An analysis of of the SRP/CS participating in the safety function must generally be performed
in accordance with the schematic Sensor / PES / Actuator.
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