Rockwell Automation Publication 2198-UM002G-EN-P - February 2019 307
Kinetix 5700 Safe Torque-off Function Chapter 9
Average Frequency of a Dangerous Failure
Safety-related systems are classified as operating in a High-demand/continuous
mode. The SIL value for a High-demand/continuous mode safety-related
system is directly related to the probability of a dangerous failure per hour
(PFH).
PFH calculation is based on the equations from IEC 61508 and show worst-
case values. Table 149
provides data for a 20-year proof test interval and
demonstrates the worst-case effect of various configuration changes on the
data.
Table 149 - PFH for 20-year Proof Test Interval (STO function)
Safe Torque-off Feature
The safe torque-off (STO) circuit, when used with suitable safety components,
provides protection according to ISO 13849-1 (PL e), according to
IEC 61508, IEC 61800-5-2, and IEC 62061 (SIL CL 3). All components in
the system must be chosen and applied correctly to achieve the desired level of
operator safeguarding.
The 2198-xxxx-ERS3 and 2198-xxxx-ERS4 STO circuit is designed to turn
off all of the output-power transistors when the STO function is requested.
You can use the 2198-xxxx-ERSx STO circuit in combination with other
safety devices to achieve a Stop Category 0 stop as described in Stop Category
Definition on page 306, and protection-against-restart as specified in IEC
60204-1.
IMPORTANT Determination of safety parameters is based on the assumptions that
the system operates in High-demand mode and that the safety function
is requested at least once every three months.
Attribute
2198-Sxxx-ERS3
Single-axis Inverters
2198-Dxxx-ERS3
Dual-axis Inverters
PFH (1e-9) 1.57 1.64
HFT (hardware fault tolerance)
(1)
(1) Hardware fault tolerance is the minimum number of faults that can cause a loss of the safety function as defined by IEC 61508-2.
11
Proof test (years) 20 20
ATTENTION: The safe torque-off (STO) feature is suitable only for performing
mechanical work on the drive system or affected area of a machine. It does
not provide electrical safety.
SHOCK HAZARD: In Safe Torque-off mode, hazardous voltages can still be
present at the drive. To avoid an electric shock hazard, disconnect power to
the system and verify that the voltage is zero before performing any work on
the drive.
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