Altivar Process ATV680 - Safety Function STO (Safe Torque Off)

18 EAV64334 06/2017
Safety Function STO (Safe Torque Off)
Overview
This function brings the machine safely into a no-torque state and / or prevents it from starting accidentally.
The safe torque-off (safety function STO) function can be used to effectively implement the prevention of
unexpected start-up functionality, thus making stops safe by preventing the power only to the motor, while
still maintaining power to the main drive control circuits. The principles and requirements of the prevention
of unexpected start-up are described in the standard EN 1037:1995+A1.
The logic inputs (STOA
and STOB) are always assigned to this function.
The safety function STO status can be displayed using the HMI of the drive or using the commissioning
software.
(1) Motor speed - (2) Actual speed - (3) STOA
and STOB - STO Activation - (4) Time
NOTE: If delay between STOA
and STOB is greater than 1 s, the safety function STO is triggered and an
error is triggered with the error code [Safety Function Error] SAFF.
Safety Function STO Standard Reference
The safety function STO is defined in section 4.2.2.2 of standard IEC 61800-5-2 (edition 1.0 2007.07):
Power that can cause rotation (or motion in the case of a linear motor), is not applied to the motor.The
PDS(SR) (power drive system suitable for use in safety-related applications) will not provide energy to the
motor which can generate torque (or force in the case of a linear motor).
 NOTE 1: This safety function corresponds to an uncontrolled stop in accordance with stop category 0
of IEC 60204-1.
 NOTE 2: This safety function may be used where power removal is required to prevent an unexpected
start-up.
 NOTE 3: In circumstances where external influences (for example, falling of suspended loads) are
present, additional measures (for example, mechanical brakes) may be necessary to prevent any
hazard.
 NOTE 4: Electronic equipment and contactors do not provide adequate protection against electric
shock, and additional insulation measures may be necessary.
DANGER
ELECTRIC SHOCK CAUSED BY INCORRECT USE
The safety function STO (Safe Torque Off) does not cause electric isolation. The DC bus voltage is still
present.
 Turn off the mains voltage using appropriate switch to achieve a voltage-free condition.
Failure to follow these instructions will result in death or serious injury.