Standards and certifications
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Mobile Panel 7100 User's manual 1.51
In electrical and electronic systems, faults that must be detected include cross faults between circuits, interruptions,
short circuits or stuck contacts. Specially certified safety relays with their own specific PL are often used for detecting
faults in the individual safety circuits. The overall PL necessary for the safety function is only achieved, however,
if the connection with the corresponding circuits has also been implemented for the respective PL in accordance
with the product description and the PL of all components contributing to the safety function have been taken into
account.
The PL for an overall safety function must therefore always be calculated from the individual components or mod-
ules.
Standard EN ISO 13849-1 provides guidelines for more easily determining the PL for a safety function consisting
of multiple components.
Note that with safety components connected in series, the PL of the safety function is determined by the safety
component with the lowest PL in the safety function. For example, a safety function consisting of 3 components
with category 4 PL e, category 3 PL d and category 2 PL c would result in a performance level of PL c for the overall
safety function. In addition, it is important to note that a fault would result in the loss of the safety function even
though category 4 PL e components are integrated in the safety function. This is because one of the components
being used is only category 2.
Combining several PLs can reduce the overall PL.
A FMEA (failure mode and effects analysis) can ensure that a fault will not lead to the loss of the safety function. This
is done by theoretically, or even practically, running through all possible faults and showing that the requirements
of the category are sufficiently fulfilled.
5.2.8 Restart interlock per EN 1037:1995 (Safety of machinery - Prevention of unexpected start-
up)
Keeping a machine in a state of rest while personnel are working in the danger zone is one of the most important
requirements for safely operating machines.
Startup refers to the transition of a machine or its parts from a state of rest to a moving state. A startup is considered
unexpected if caused by one of the following:
•
A startup command generated due to controller failure or external influences on the controller.
•
A startup command generated due to incorrect operation of a startup control actuator or another part of
the machine.
•
Restoration of the power supply after an interruption.
•
External/Internal influences on parts of the machine.
To prevent unexpected startup of machines or parts of machines, power should be removed and dissipated. If this
is not practical (e.g. frequent brief interventions in danger zones), other measures must be taken:
•
Measures to prevent randomly generated startup commands.
•
Measures to prevent randomly generated startup commands from causing unexpected startup.
•
Measures to automatically stop the dangerous part of the machine before a dangerous situation can be
caused by unexpected startup.