Risk assessment data, Safe state, Hardware fault tolerance – Rockwell Automation 20-750-ATEX PowerFlex 750-Series ATEX Option Module User Manual
Page 11: Safety reaction time
Rockwell Automation Publication 750-UM003B-EN-P - July 2013
11
Safety Concepts
Chapter 1
Risk Assessment Data
were calculated based on equations in
IEC 61508. This table shows the worst case calculated values for drive frames
1…10 with a proof test interval of 20 years.
These values show the SIL1 consumption of the ATEX safety function to be
approximately 30%. The safety calculations represent the local ATEX safety path
from the input of the ATEX daughter card to the device that disables
heat-producing power.
Table 1 - PFD and PFH for 20-year Proof Test Interval for Frames 1…10
Safe State
The safe state includes all operation that occurs outside of the other monitoring
and stopping behavior defined as part of the ATEX option module. The ATEX
safety function, as provided by the ATEX option module, places the drive in a
safe state by removing the power from the gate firing circuits of the output power
devices (IGBTs).
Hardware Fault Tolerance
Hardware fault tolerance is the minimum number of faults that can cause a loss of
the safety function as defined by IEC 61508-2. 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
ATEX safety function is 30 ms (maximum) for PowerFlex 750-Series drives,
frames 1…10.
IMPORTANT
A proof test is not defined in this user manual. A proof test interval of 20 years
is used for the calculations here, signifying the product life span is 20 years.
Attribute
Value
Safety integrity level (SIL)
1
Hardware fault tolerance (HFT)
0
Proof test interval (PTI)
20
Probability of failure on demand (PFD)
<3.09E-02
Probability of failure per hour (PFH)
<3.53E-07
IMPORTANT
If one fault occurs in the safety path, the safety function can become
compromised.