Optidrive E4, the latest general purpose variable frequency drive from Invertek Drives, includes dual-channel safe torque off (STO) certified to SIL3 as standard to provide enhanced levels of safety required in many industrial applications.

Safe torque off is activated by an emergency stop or a safety gate trigger which activates an STO signal. The STO circuit disables the Insulated-Gate Bipolar Transistor (IGBT) in the drive – preventing torque-generating energy from being supplied to the motor. The motor then coasts to a smooth stop. 

This all happens whilst the drive remains connected to the mains power supply – allowing continued monitoring and enabling faster restarts. Integrating the stop function into the VFD simplifies safety-circuit design by removing the need for extra components and wiring.  

“SIL3 certified STO is required where safety is paramount,” comments Invertek’s Product Manager Justin Walker. “For example, in machinery and manufacturing operations including CNC machining, automated cells and robotic arms. Safe torque off is also widely used in materials handling applications, high-speed packaging, heavy industry and process control, and energy production. 

“STO prevents accidental restarts during maintenance operations or emergencies – this is vital in applications where unscheduled motor operation has the potential to cause physical injury to machine operators and maintenance personnel.”  

Dual-channel STO is safer than single-channel as both independent channels must fail before torque is removed, providing Safety Integrity Level (SIL) and PL e/Cat 3 safety and performance without relying on external contactors. Using two channels ensures there is not a single point of failure in the system; this means that motor driven operations with dual-channel STO pose less risk than those with single-channel or no STO. 

“Using automation to override the risks caused by human behaviour is proven to help keep people safe. Dual-channel STO offers the ‘belt and braces’ approach to safety and is particularly valuable for machine builders who need to ensure their products are compliant with the machinery directive and international product standards,” continues Justin. “By integrating an Optidrive E4 VFD into the machine’s design, manufacturers can be confident that their customers will benefit from precise motor control, energy efficiencies and the highest levels of safety.”

Follow this link to find out more about the new Optidrive E4 with built in STO certified to SIL3.