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52 Maintenance
Safety components
The mission time of safety components is 10...20 years, depending on the component.
During this time the failure rates of electronic components remain constant. This applies to
the components of the standard Safe torque off circuit, modules, relays and other components
that are part of safety circuits. After the mission time of a component expires, the component
must be replaced with a new one.
The mission time of the safety function is 10 years. After this time, you can replace the push
button monitoring relays [A642...A64x], which extends the mission time of the safety function
by 10 years.
After a total of 20 years, the components of the safety circuit must be replaced. Note that
some of the components may already have been replaced earlier, restarting their mission
time. The remaining mission time of the whole circuit is however determined by its oldest
component.
Contact your local ABB service representative for more information.
Competence
The person who does the maintenance and proof test activities of the safety function must
be a competent person with expertise and knowledge of the safety function and functional
safety.
Residual risk
The safety functions are used to reduce the recognized hazardous conditions. In spite of
this, it is not always possible to eliminate all potential hazards. Thus, the warnings for the
residual risks must be given to the operators.
Intentional misuse
The safety circuit is not designed to protect a machine against intentional misuse.
Decommissioning
When you decommission an emergency stop circuit or an inverter unit, make sure that the
functional safety of the machine is maintained by other means until the decommissioning
is completed.
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