Rockwell Automation Publication 750-UM002H-EN-P - February 2017 11
Safety Concept Chapter 1
Stop Category Definitions
The selection of a stop category for each stop function must be determined by a
risk assessment.
• Stop Category 0 is achieved with immediate removal of power to the
actuator, resulting in an uncontrolled coast to stop. Safe Torque Off
accomplishes a Stop Category 0 stop.
• Stop Category 1 is achieved with power available to the machine
actuators to achieve the stop. Power is removed from the actuators when
the stop is achieved.
Performance Level and Safety Integrity Level (SIL) CL3
For safety-related control systems, Performance Level (PL), according to
EN ISO 13849-1, and SIL levels, according to IEC 61508 and EN 62061,
include a rating of the system’s 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.
Refer to the EN ISO 13849-1, IEC 61508, and EN 62061 standards for
complete information on requirements for PL and SIL determination.
Functional Proof Tests
The functional safety standards require that functional proof tests be
performed on the equipment used in the system. Proof tests are performed at
user-defined intervals and are dependent upon PFD and PFH values.
IMPORTANT When designing the machine application, consider timing and distance for a
coast to stop (Stop Category 0 or Safe Torque Off). For more information
regarding stop categories and Safe Torque Off, refer to EN 60204-1 and
EN 61800-5-2, respectively.
IMPORTANT Your specific application determines the time frame for the proof test
interval.
Verify operation of safety function after drive installation, modification, or
maintenance. Refer to Verify Operation
on page 27 for more information.
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