104/641 Bosch Rexroth AG | Tightening Technology 3 608 878 300
System 350 | 3 608 878 300/2019-03
Calculation basis PL and PFHd or MTTFd
For the Rexroth Tightening System 350, the PFHd or MTTFd value is specified in addition to the
performance level (PL). As within the safety function of the tightening system, one uses also
electromechanical components with a limited number of switching cycles, the following scenario is
assumed for calculating the PFHd value:
• A cycle takes 15 seconds
• The system is operated in 3-shift operation without standstill days, i.e. Sundays, public holidays,
company holidays, etc.
These assumptions result in a value of 2.1 million switching cycles per year.
CAUTION
Risk of injury due to non-compliance with the system-specific requirements
on an emergency OFF system.
Risk of short circuit, risk of injury.
The user is obliged to maintain the system-specific requirements for an emergency OFF system.
When designing the emergency OFF circuit, the user must observe the rules for the short-circuit-
and cross-circuit-proof laying. When using external mains contactors in superior emergency OFF
circuits, observe the restarting time for the component.
Check that the emergency OFF circuit is functioning correctly before commissioning the
tightening system.
Observe the local, system-specific regulations and requirements; proper use of tools, lifting, and
transport equipment; as well as the relevant standards, provisions, and accident prevention
regulations.
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