Rockwell Automation Publication 750-UM003D-EN-P - March 2017 13
Safety Concepts Chapter 1
Hardware Fault Tolerance
Hardware fault tolerance is the minimum number of faults that can cause a loss
of the safety function as defined by EN 61800-5-2 and IEC 61508 part 2. The
overall ATEX function has a hardware fault tolerance of zero.
Safety Reaction Time
The safety reaction time is the amount of time from a safety-related event as
input to the system until the system is in the safe state.
The safety reaction time from an input signal trigger to the initiation of the
ATE X safet y f unction.
Table 1 - Safety Reaction Time
Contact Information If Safety
Option Failure Occurs
If you experience a failure with any safety-certified device, contact your local
Allen-Bradley distributor to do the following:
• Return the device to Rockwell Automation so the failure is
appropriately logged for the catalog number that is affected and a record
is made of the failure.
• Request a failure analysis (if necessary) to determine the probable cause
of the failure.
IMPORTANT If one fault occurs in the safety path, the safety function can become
compromised.
Drive Safety Reaction Time
PowerFlex 753 drives
30 ms (max)
PowerFlex 755 drives
PowerFlex 755TL low harmonic drives
PowerFlex 755TR regenerative drives
PowerFlex 755TM drive systems
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