ABB Drives has produced a white paper on developing safer machines with drive based functional safety.  The paper is divided into three sections covering: Functional Safety: Safer machines with drive-based functional safety; Laws, Standards and a road-map to drive-based functional safety, and ABB’s drive-based functional safety solutions.

Compared to the traditional safety solution, integrated drive-based functional safety includes the same functionality but is integrated into the drive. The most basic functionality level is the STO circuit inside the drive which can safely disable the drive’s power stage, eliminating the need for a motor contactor. Upon activation STO immediately switches off the drive output to the motor, which coasts to a stop.

Safe torque off (STO) is the required basic foundation for drive-based functional safety, that can safely disable the drive’s power stage.  STO is typically used for prevention of an unexpected start-up (EN 1037) of machinery or for an emergency stop, fulfilling stop category 0 (EN 60204-1).

By integrating safety functions inside the drive eliminates the use of costly external safety add-ons like contactors, safety relays, etc. Using integrated drive-based functional safety results in cleaner installation and lower costs, with fewer components needed to reach the required SIL or PL.

Benefits

For the machine builder there are a number of benefits in using integrated drive-based functional safety.  Safety functionality is seamlessly integrated into the drive operation, so there is less wiring which save time and cost.

For the end user, using STO as the motor switch off path, instead of a contactor, is faster and saves money, space, and wear/maintenance.  With STO there is no need to power off the drive or use an output contactor for prevention of unexpected start-up, enabling faster restarts and eliminating any need for resetting a position referenced etc. Additionally, there are no external parts needed to be changed or maintained

ABB UK’s offering of low voltage AC drives with STO as a standard feature includes ACS880, ACS580, ACS850, ACS355, ACQ810, ACSM1 and MicroFlex e150. The ACS800 drives have STO built-in as an optional feature.

When additional integrated safety functions are needed, ABB’s optional TÜV-certified safety functions module FSO-11 are available.  The FSO-11 works seamlessly with the all-compatible ACS880 drives and can be used in systems up to SIL 3/PL e. This compact safety module offers several safety functions including: Safe stop 1 (SS1), Safe stop emergency (SSE), Safe brake control (SBC), Safety-limited speed (SLS), Safe maximum speed (SMS) and prevention of unexpected start-up.

Go here to open ABB’s white paper

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