Rockwell Automation 21G PowerFlex 750 Series Safe Torque Off - Manual (Page 10)

10 Rockwell Automation Publication 750-UM002F-EN-P - July 2013
Chapter 2 Safety Concept
Safety Category 3 Performance Definition
To achieve Safety Category 3 according to ISO 13849-1:2006, the safety-related
parts have to be designed such that:
• the safety-related parts of machine control systems and/or their protective
equipment, as well as their components, shall be designed, constructed,
selected, assembled, and combined in accordance with relevant standards
so that they can withstand expected conditions.
• basic safety principles shall be applied.
• a single fault in any of its parts does not lead to a loss of safety function.
• the average diagnostic coverage of the safety-related parts of the control
system shall be medium.
• the mean time to dangerous failure of each of the redundant channels shall
be high.
• measures against common cause failure shall be applied.
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.
IMPORTANT When designing the machine application, timing and distance should be
considered for a coast to stop (Stop Category 0 or Safe Torque Off). For more
information regarding stop categories, refer to EN 60204-1.