Allen-Bradley PowerFlex 527, User Manual

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88 Rockwell Automation Publication 520-UM002B-EN-E - December 2017
Chapter 4 PowerFlex 527 Integrated Safe Torque-Off
Category 3 Requirements According to ISO 13849
Safety-related parts are designed with these attributes:
• A single fault in any of these parts does not lead to the loss of the safety
function.
• A single fault is detected whenever reasonably practicable.
• Accumulation of undetected faults can lead to the loss of the safety
function and a failure to remove motion producing power from the motor.
Stop Category Definition
Stop category 0 as defined in EN 60204 or Safe Torque-Off as defined by
EN 61800 5 2 is achieved with immediate removal of motion-producing power
to the actuator.
Performance Level (PL) and Safety Integrity Level (SIL)
For safety-related control systems, Performance Level (PL), according to
EN ISO 13849, and SIL levels, according to EN 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, EN 61508, and EN 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 allow torque ceases, all of the drive output-power
transistors are released from the On state. This results in a condition where the
motor is coasting (stop category 0). Disabling the power transistor output does
not provide mechanical isolation of the electrical output that is required for some
applications.
The PowerFlex 527 drive STO function response time is less than 12 ms.
Response time is the delay between the time the drive STO function receives the
STO request and the time when motion producing power is removed from the
motor.
IMPORTANT
In the event of a malfunction, the most likely stop category is category 0.
When designing the machine application, timing and distance must be
considered for a coast to stop. For more information regarding stop categories,
refer to EN 60204-1.