4 Rockwell Automation Publication SAFETY-AT140A-EN-P - May 2015
Safety Function: Actuator Subsystems – Stop Category 1 via the PowerFlex 525 and PowerFlex 527 Drives with Safe Torque-off
control reliable. Each safety product has its own rating and can be combined to create a safety function that meets or
exceeds the PLr.
Stop Safety Functions
This application technique includes two safety functions:
1. Safety-related stop function initiated by a safeguard.
2. Prevention of an unexpected startup.
Safety Function Requirements
Safety-related Stop Function Initiated by a Safeguard
When a partial-access guard door is opened, the Input subsystem initiates and maintains a stop command for the safety
system to stop hazardous motion before a person can reach the hazardous area. The stop command cannot be reset until the
guard door is closed.
Prevention of an Unexpected Startup
The safety system cannot be reset, and hazardous motion cannot be restarted while the guard door is open. Once the guard
door is closed and the stop command is reset, a second action (pressing a Start button) is required before the hazardous
motion can resume. This document presumes that the Start/Stop button is connected to and controlled by the
programmable automation controller (PAC).
From: Risk Assessment (ISO 12100)
1. Identification of safety functions
2. Specification of characteristics of each function
3. Determination of required PL (PLr) for each safety function
To: Realization and PL Evaluation
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