QSHT 5700 Inverter Safe Torque-off Function
Introduction
QuickStick HT User Manual 265
Rockwell Automation Publication MMI-UM007F-EN-P - September 2020
Performance Level (PL) and Safety Integrity Level (SIL)
For safety-related control systems, Performance Level (PL), according to ISO 13849-1, and
SIL levels, according to IEC 61508 and IEC 62061, include a rating of the systems ability to
perform its safety functions. All of the safety-related components of the control system must
be included in both a risk assessment and the determination of the achieved levels.
See the ISO 13849-1, IEC 61508, and IEC 62061 standards for complete information on
requirements for PL and SIL determination.
Average Frequency of a Dangerous Failure
Safety-related functions are classified as operating in a High-demand/continuous mode. The
SIL value for a High-demand/continuous mode safety-related function is directly related to
the probability of a dangerous failure per hour (PFH).
PFH calculation is based on the equations from IEC 61508 and shows worst-case values.
Table 7-1 provides data for a 20-year proof test interval and demonstrates the worst-case
effect of various configuration changes on the data.
IMPORTANT Determination of safety parameters is based on the assump-
tions that the system operates in High-demand mode and that
the safety function is requested at least once every three
months.
Table 7-1: Safety Circuit Relevant Parameters
Attribute
MMI-HT-C2198-D032
Inverter
Hardware Fault Tolerance (HFT)
*
* Hardware fault tolerance is the minimum number of faults that the safety sys-
tem can tolerate without a loss of the safety function as defined by IEC
61508-2.
1
Mode of operation High-demand/continuous
STO function components type
according to IEC 61508-2
Type B
PFH (1e-9/hour) 1.89
MTTFd 195 years
Proof Test Interval
â€
†No proof test-related maintenance is required within 20 years mission time.
20 years
Diagnostic Coverage (DC) 90%
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