Mitsubishi Electric MELSEC iQ-R Series Safety Manual page 25

Category
The category is a classification of safety function sustainability for the safety system. As shown in the following, categories
can be classified into the items, according to the safety requirements and safety function sustainability.
The following table shows the requirements of standard for categories.
Category Summary of requirements
B • Achieve desired functions of the safety-related parts of
the machine control systems.
1 • Requirement of B shall apply.
• Use well-tried and high-performance components.
2 • Requirement of B shall apply.
• Check safety functions at suitable intervals.
3 • Requirement of B shall apply.
• A single fault does not lead to loss of the safety
functions.
• The single fault is detected whenever reasonably
practicable.
4 • Requirement of B shall apply.
• A single fault can be detected when performing or
before performing the safety functions
• An accumulation of faults shall not lead to loss of the
safety functions.
(For details, refer to ISO13849-1: 2006)
Sustainability of safety functions
• The occurrence of a fault can lead to loss of
the safety functions.
• Similar to the category B, reliability of
functions to ensure safety is high.
• The loss of the safety functions can be
detected by the checks, however, the safety
functions may be lose depends on the
timing of the checks.
• When a single fault occurs, the safety
functions are always performed.
• Some but not all faults will be detected.
Accumulation of undetected faults can lead
to loss of the safety functions.
• When the faults occur, the safety functions
are always performed.
• The faults will be detected in time to prevent
loss of the safety functions.
3 RISK ASSESSMENT AND SAFETY LEVEL
Features of the
functions
Mainly characterized by
selection of components
Mainly characterized by the
system configuration method
to ensure safety.
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