Technical Description: Implementing a Safely-Limited Speed Function with ABB ACS880-01 and AC500-S

This document details the design and implementation of a safely-limited speed (SLS) safety function. It utilizes the ABB ACS880-01 industrial drive and the AC500-S safety PLC, along with other ABB safety devices. The safety function is implemented in accordance with machinery standards EN/IEC 62061, EN ISO 13849-1, EN/IEC 60204-1, and EN/IEC 61800-5-2. Necessary SIL/PL calculations are presented using ABB's Functional Safety Design Tool.

Safer Machines with Drive-Based Functional Safety

Drive-based safety functions are employed in applications requiring risk reduction from hazardous movements. The objective is to design machines that are safe to operate. This safety function example, presented for specific drive and safety devices, can be adapted for other ABB drives with minor modifications.

ACS880-01 industrial drives can be connected with the AC500-S safety PLC to implement a safely-limited speed (SLS) safety function. This function ensures that the motor speed does not exceed a specified limit, allowing machine interaction, such as maintenance or cleaning, to be performed at a reduced speed without stopping the drive.

System Components

The system comprises the following key components:

• ACS880-01 R5 drive
• Eden OSSD non-contact safety sensor
• AC500-S safety PLC
• PROFIsafe encoder

The diagram illustrates the system architecture, showing an ACS880-01 industrial drive, an Eden OSSD non-contact safety sensor, an AC500-S safety PLC, and a PROFIsafe encoder connected in a functional safety setup.

Safely-Limited Speed Function Details

Overview of the Safety Function

The safely-limited speed (SLS) function ensures that the motor's specified speed limit is not exceeded. In ABB drive solutions, the SLS function can automatically decelerate the motor to a speed below the defined limit when activated. Both time and ramp monitoring can be utilized during deceleration. The SLS function is suitable for maintaining a machine at a predefined safe speed and preventing acceleration during operations like maintenance or cleaning.

Figure 1 is a graph depicting speed versus time. It illustrates the Safely-Limited Speed (SLS) function in operation, showing a controlled deceleration phase ('Ramp SLS active monitoring') where the motor speed is brought below a specified limit.

Operation of the Safety Function

Upon activation of the Eden sensor, the AC500-S detects the signal and activates the SLS function. If the motor speed exceeds the defined SLS speed limit, the drive first decelerates to a speed below the SLS limit. During this transition, the AC500-S monitors the ramp using the PROFIsafe encoder. Once the motor speed is below the SLS speed limit, the AC500-S begins continuous SLS monitoring to ensure the speed does not exceed the specified level. This monitoring persists until the SLS function is deactivated.

Returning the Eden sensor to its standby position deactivates the SLS safety function. The system will then automatically resume operation or require a manual reset, depending on the application's configuration and requirements. If the SLS function trips (e.g., due to overspeed activating Safe Torque Off - STO), a manual reset is mandatory.

Design of the Safety Function

The design of the SLS function involves an Eden non-contact safety sensor acting as an activating switch, a safety PLC serving as the logic unit with an encoder providing speed feedback, and a Safe Torque Off (STO) circuit within the ACS880-01 drive functioning as the actuator. The STO circuit stops the drive if the speed exceeds the allowed SLS limit. Refer to Figure 2 for connection details.

Figure 2 presents a connection example diagram for the safely-limited speed function. It shows the integration of an Eden OSSD safety sensor, an AC500-S safety PLC, and an ACS880-01 drive, utilizing a PROFIsafe encoder for speed feedback. The diagram also indicates software versions and safety integrity levels (PL/PFHd) for each component.

Ensuring the Required Safety Performance

The safety function must meet the required safety performance levels determined by a risk assessment. ABB's Functional Safety Design Tool (FSDT-01) is utilized to design the desired safety function. This process follows these steps:

1. Evaluate risks to establish the target safety performance (SIL/PL level) for the safety function.
2. Design the safety function loop and verify the achieved performance level (PL) or safety integrity level (SIL) for the loop, according to EN ISO 13849-1 or EN/IEC 62061, respectively, using device safety data and application-specific characteristics.
3. Generate a report for machine documentation, including all calculation results and assumptions made during application design.

Figure 3 details the safety calculation and design process for the safely-limited speed function, adhering to EN ISO 13849-1. It includes a breakdown of system components (safety sensor, speed encoder, safety PLC logic, drive), their safety performance levels (PL), probability of dangerous failures per hour (PFHd), and contribution to the total PFHd. The overall system achieves PL d (SIL 2).

Finally, the implemented safety function is validated against the risk assessment to ensure it effectively reduces the targeted risk.

Safety Function Verification and Validation

In addition to safety calculations for achieving the required safety performance (SIL/PL), the safety function must also be functionally verified.

General Considerations

Achieving machinery safety requires a systematic approach that extends beyond the physical implementation of a safety function. Overall machinery safety typically encompasses the following areas:

• Planning for and managing functional safety throughout the machine's lifecycle.
• Assuring compliance with local laws and requirements, such as the Machinery Directive and CE marking.
• Assessing machine risks through analysis and evaluation.
• Planning risk reduction and establishing safety requirements.
• Designing the safety functions.
• Implementing and verifying the safety functions.
• Validating the safety functions.
• Documenting the implemented functions and the results of risk assessment, verification, and validation.

Further Information

For more information concerning functional safety and the Functional Safety Design Tool, visit www.abb.com/safety or consult ABB's Technical Guide no. 10.

Abbreviations

Note: This is an indicative example. Relevant installation, design, and safety calculations need to be specifically completed for each system implementation according to machinery safety standards (EN/IEC 62061, EN ISO 13849-1, EN/IEC 60204-1, and EN/IEC 61800-5-2). ABB does not take responsibility for the accuracy of the data used in this document and reserves the right to make changes without further notice. For detailed safety function implementation, please contact your local ABB representative.

Contact Information

For more information, visit:

• www.abb.com/drives
• www.abb.com/drivespartners

Copyright 2014 ABB. All rights reserved. Specifications subject to change without notice.

Document reference: 3AUA0000172916 REV A EN 22.12.2014 #17363