Rockwell Automation Publication 2198-UM001M-EN-P - November 2022 167
Chapter 10 Kinetix 5500 Safe Torque Off - Integrated Safety
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 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.
Description of Operation The Safe Torque Off (STO) feature provides a method, with sufficiently low
probability of failure, to force the power-transistor control signals to a disabled
state. When the command to execute the STO function is received from the
GuardLogix controller, all drive output-power transistors are released from the
ON-state. This results in a condition where the drive is coasting. Disabling the
power transistor output does not provide mechanical isolation of the electrical
output that is required for some applications.
The 2198-Hxxx-ERS2 drive STO function response time is less than 10 ms.
Response time is the delay between the time when the drive STO function
receives the integrated safety packet with an STO request and the time when
motion producing power is removed from the motor.
STO State Reset
The 2198-Hxxx-ERS2 servo drives support both manual and automatic restart
types for exiting the STO state.
• Manual restart indicates a transition from 0 to 1 on the SO.Reset tag is
required to allow torque after the SO.SafeTorqueOff tag has transitioned
from 0 to 1.
• Automatic restart indicates that torque will be allowed only by
transitioning the SO.SafeTorqueOff tag from 0 to 1. The SO.Reset tag is
used only for resetting safety faults.
See Figure 79
for an understanding of the 2198-Hxxx-ERS2 STO-state manual
restart functionality.
IMPORTANT 2198-Hxxx-ERS2 servo drives enter the STO state if any STO function
fault is detected.
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