| Category |
Summary
of requirements |
System
behavior |
Main
principle to achieve safety |
| B |
Safety related parts of machine control systems
and/or their protective equipment, as well as their components,
shall be designed, constructed, selected, assembled and combined
in accordance with the state of the art so they can withstand
the expected influence. |
The occurence of a fault can lead to the loss
of the safety function |
Mainly characterized by selection of components |
| 1 |
Requirements of B shall apply.
Well-tried components and well-tried safety principles
shall be used.
|
The occurrence of a fault can lead to the loss
of the safety function but the probability of occurrence is
lower than for category B. |
| 2 |
Requirements of B and the use of
well-tried safety principles shall apply.
Safety function shall be checked at suitable intervals
by the machine control system.
|
The occurrence of a fault can lead to the
loss of the safety function between the checks.
The loss of safety function is detected by the check.
|
mainly characterized by structure |
| 3 |
Requirements of B and the use of
well-tried safety principles shall apply.
Safety-related parts shall be designed, so that:
- a single fault in any of these parts does not lead to
the loss of the safety function, and
- whenever reasonably practicable the single fault is
detected.
|
When single fault occurs the safety function
is always performed.
Some but not all faults will be detected.
Accumulation of undetected faults can lead to the loss
of the safety function.
|
| 4 |
Requirements of B and the use of
well-tried safety principles shall apply.
Safety related parts shall be designed, so that:
- a single fault in any of these parts does not lead
to the loss of the safety function
- the single fault is detected at or before the next
demand upon the safety function. If this is not possible,
then an accumulation of faults shall not lead to a loss
of the safety function.
|
When faults occur the safety function is
always performed.
The fault will be detected in time to prevent the loss
of the safety function.
|
