BBH SCU Series, Руководство по установке

Страница: 171 / 303

18
Information for design,
programming, validation and test
HB-37500-810-11-16F-EN SCU Installation Manual - Master and Slaves - SARC Page 171 of 303
Status: 09.06.2022
18.3.3. Software specification
The software specification refers to the preceeding specification of the safety functions.
The software specification can also be replaced by an accordingly elaborated specification
of the safety functions if this specification of the safety function contains all requirements
(cf. the example under 12.3.3.3).
It is recommended to create an extracted list.
This extracted list should contain the following information:
• Designation of the safety function
• Description of the safety function
• Parameters if available
• Triggering event / operating state
• Reaction / output
The specification should be deatailed enough to be suitable for a later validation of the
programming.
18.3.4. Hardware specification
In the hardware specification describes the complete plant structure, and especially the
components used within the plant structure together with their specific identification data.
The hardware specification serves as basis for the determination of the achieved safety
level. The achieved safety level is determined on the basis of the architecture and of the
identification data of all devices that participate in a safety function.
Furthermore, in the hardware specification also the constructive protective measures
against systematic errors and Common Cause errors must be indicated.
18.3.5. Selection of the SRP/CS and selection of the equipment
For every safety function, the SRP/CS (Safety related parts of control system) must be
selected in a way that is suitable to achieve the desired safety level for every safety
function. In an overall survey of the plant structure, the components with security-related
functions must be indicated, and they must be assigned to the particular safety functions.
The safety indices of the components with security-related functions must be determined.
The safety indices include the following values:
MTTFd = mean time to failure (dangerous) = the mean time until the dangerous failure
occurs)
DC avg = average diagnostic coverage range
CCF = common cause failure, failure due to a common cause