schmersal PSC1 - Hardware and Software Design; Check of the Hardware Design; Iterative Check on the Safety Level Achieved

Installation manual
HB-37420-810-01-25F-EN PSC1-C-100 Installation manual - V2.2.docx Page 188 of 201
Version: 25F
12.3.6 Hardware and software design
The specifications from the hardware and software specification are implemented in the
actual system design.
The specifications for the components to be used and their circuitry from the hardware
specification are to be met as are the specifications for the fault exclusions. Both are to be
safeguarded using suitable means and are to be documented.
The specifications from the software specification are also to be followed and fully
implemented in the software.
In addition, the higher-level specifications for the software from safety-related programming
must be observed. These include:
• Modular and clearly structured layout of the program
• Assignment of functions to the safety functions
Comprehensible depiction of the functions by means of:
• Unambiguous identifiers
• Comprehensible comments
• Wide-ranging use of tested functions/function blocks
• Defensive programming
12.3.7 Check of the hardware design
On completion of the planning, the hardware design is to be checked for compliance with the
specifications from the hardware specification.
In addition, compliance with the specific safety level for each individual safety function is to
be checked by means of suitable analysis. The analytical methods are described in the
applicable standards (e.g. EN ISO 13849-1).
Circuit diagram analysis:
Compliance with the safety-related aspects of the specifications is to be checked based on
the circuit diagram and the parts list.
In particular, to be checked are:
• The component connection circuitry as per specifications
• The dual-channel layout as far as specified
• The freedom from interaction of parallel, redundant channels
• The use of components as per specifications
• The check must be made by means of a traceable analysis
12.3.7.1 Iterative check on the safety level achieved
The safely level achieved is to be determined based on the circuit layout (= architecture
single-channel / dual-channel / with or without diagnostics), the device characteristic data
(information from manufacturer or appropriate sources) and the diagnostic coverage
(information from manufacturer of PES or general sources). The appropriate methods are to
be found in the underlying safety standard.