3.5 Categories of Safe Stop
International standard EN/ISO 13850 specifies the functional requirements and design principles of emergency stop devices.
It applies to all machines, whatever type of energy is used to control this function.
The standard allows 2 types of stop:
• Category 0 stop: Stopping by immediately cutting-off power or mechanical disconnection between the dangerous components.
• Category 1 stop: Controlled stopping with power maintained to the actuator to achieve stopping (braking for example), then cut-
off of power when 0 speed is reached.
During a category 0 stop, the motor coasts down in an uncontrolled way. If access to the machine coasting down involves a hazard
(results of the hazard and risk analysis), take protective measures to avoid the hazard.
Refer to EN IEC 61800-5-2:2007 (4.2.2.2) for a definition of Safe Torque Off (STO).
A Category 1 stop triggers a controlled stop. The safety option monitors the controlled stop. If a power outage or an error occurs, a
controlled stop is impossible. Trigger the safety function Safe Torque Off after the stop to shut off the motor torque.
Refer to EN IEC 61800-5-2:2007 (4.2.2.3) for a definition of Safe Stop 1 (SS1).
An evaluation of the machine-related risks determines which of the 2 stopping methods to use.
NOTICE
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, refer to EN IEC 60204-1.
3.5.1 Operation and Requirements
The safety option is redundant and self-checking. It requires digital input signals from an input sensor (for example PNP proximity
switch) or higher resolution TTL or HTL encoders to monitor for either safe stop or speed conditions.
3.5.2 Safety Functions
Safety functions maintain a safe condition or prevent hazardous conditions from arising. The safety functions for drives are defined in
EN IEC 61800-5-2.
The safety option implements the following safety functions:
• Safe Torque Off (STO)
- No power is being fed to the motor which can generate a rotation. Stop category 0 to EN IEC 60204-1.
• Safe Stop 1 (SS1)
- Motor decelerates. Monitoring of deceleration ramp and Safe Torque Off following 0 speed, or Safe Torque Off at the end of a
deceleration time. Stop category 1 to EN IEC 60204-1.
• Safely limited speed (SLS)
- Prevents exceeding a defined speed value.
The safety option implements the following safety functions
Functions and Systems Overview
Installation Guide | VLT® Safety Option MCB 150/151
AQ279747441421en-000101 / 130R0292
20 | Danfoss A/S © 2018.09
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