Take integrated safety a step further
Integrated functional safety in variable speed drives is nothing new, but now new developments in drive technology can allow safety features to be integrated more seamlessly with wider process architecture, as Liam Blackshaw, UK Product Manager – LV Drives at ABB, explains.
If a process or procedure suddenly goes wrong in an industrial setting, you want it to stop as quickly and as safely as possible. Most modern variable speed drives (VSDs) are already equipped with multiple safety features. A number of the more familiar safety features are relatively basic. For instance, safe torque off carries out the function of a mechanical safety contactor in bringing a machine to a complete stop when activated. Not only can it react faster than a mechanical contactor, but it also takes up less cabinet space. As applications have grown more complex over time, an increasing variety of types of motor stops and slowdowns are required for different types of machines. Many of these can be carried out by the drive itself, enhancing safety while reducing the need for additional cabinet devices.
Stopping and slowing down a motor are in theory relatively simple tasks. Recent developments in drive technology are enabling more sophisticated integration of safety within process systems. ABB’s FSPS-21, enables safety functions to be integrated on certain ABB drives at a much lower cost. This is achieved by using PROFIsafe and PROFINET communication protocol standards to integrate PLC function with drive function. This can be performed with any safety PLC which supports PROFIsafe and PROFINET, and ultimately means that fewer components are required, decreasing the complexity of an installation without compromising on safety.
Drives equipped with the FSPS-21 module are well-suited to situations where only a small number of I/Os are required, as the in-built communication protocols can carry out of the majority of the most essential safety functions. Moreover, because the VSD’s safety functionality is governed by the PLC, STO and SS1 (Safe Stop 1) can be immediately – and safely – activated when called upon to perform an emergency stop, manual shutdown, or a wide range of other parameters such as detected overspeed.
Some applications already use a safety PLC, so ABB’s FSPS-1-equipped VSDs save duplicating programming safety functions programming because PROFIsafe and PROFINET communication are integral to the drive and can be programmed predominantly within the PLC. The result is that, when required anywhere across the system, drive-based safety functions can be activated by the PLC, and not just rely on detection by an individual drive. The FSPS-21 module complies with SIL 3 and PLe safety levels.
ABB’s FSPS-21 module removes the need to wire and connect drive logic with safety relays and contactors, as the safety functions are already predesigned within the module to make commissioning easy. It also enables safety functions for multiple drives and machines to be maintained from a single controller. The module also allows drives to be grouped according to an application’s applicable safety zones. For instance, when a conveyor line drive’s overspeed may require all associated drives to stop, this can be done by simply activating the integrated STO once for the whole group.
Automation systems traditionally required many external add-on devices to ensure their safety, but purchasing, installing and programming those additional devices is no longer a necessity. This is a benefit to many because it not only simplifies the provision of critical safety functions within a system, but it also avoids having to deal with the increasing complexity of installing such features after the fact.
Many industrial environments have long been fraught with potential danger, so integrated functional safety in drives is not a wholly new concept. However, combining safety functionality with a PLC system can better ensure that safety features are triggered exactly where and when they’re needed without compromising on productivity or the longevity of the machines.
