KFU 2-/4-
5
1Safety instructions for “Safe torque off” function (STO)
The function “Safe torque off” (STO) is a function-safeguard which protects persons and avoids material damage
in professional engineering and installation conditions as well as intended use. The function does not switch the
machine to a de-energized state.
Install an emergency-stop device according to EN 60204 to de-energize the machine, for example for
maintenance work.
For personal safety and to prevent material damage comply with the following instructions.
Warning!
Improper installation of the safety technique can cause an uncontrolled starting of the drive. This
can result in death, serious injury or material damage.
Only qualified staff may install and commission the safety functions.
The STO (Safe torque off) function does not allow emergency switch-off according to standard
EN 60204. Emergency switch-off can be realized by a mains contactor installation.
Emergency switch-off according to EN 60204 must be functioning in all operation modes of the
frequency inverter. The reset of emergency switch-off may not cause an uncontrolled starting of
the drive.
The drive restarts if the function STO is not requested any more. According to EN 60204 the drive
may only start after an acknowledgement.
Without a mechanical brake the drive might not stop immediately; but coast down. Risk of injury or
material damage has to be prevented by providing additional safety devices.
If risk of injury is possible after the motor power supply is switched off by the STO function the
access to the danger area must be locked. The access to the danger area must be locked until the
drive is come to a standstill.
Check the safety function in periodic maintenance according to your risk assessment. We
recommend an inspection latest after one year.
The STO function is one-fail-safe. No single fault or component failure can cause a disabled drive
to produce motor shaft torque. Only in extremely unlike combinations of component faults the
motor shaft could move jerky with sudden acceleration (maximum 180°/number of pole pairs, for
example jerky movement of 90° for 4-pole motor, 180°/2) and produce torque. It must be
checked, if this behaviour can cause a dangerous machine movement.
If the safety function STO is applied comply with the special safety-, installation- and operating
instructions.
Warning! Dangerous voltage!
The safety function „Safe torque off“ is practical only for mechanical work on driven machines, but not
for work on live-line voltage-carrying components.
Before working (maintenance) on live-line voltage-carrying components electrical isolation from
mains supply is necessary by a main switch.
When the 24VDC power supply is switched off the mains voltage is still alive at the DC link circuit.
Although the motor is de-energized, in standstill or coasts down the motor terminals live with high
voltage.
The motor is not electrically isolated from the DC link circuit of the frequency inverter if the „Safe
torque off“-function is activated and the motor is de-energized. High voltage may live at the motor
terminals.
Do not touch voltage-carrying contacts.
Note:
According to the EU Machinery Directive 98/37/EG the machine must be subjected to a risk
assessment, carried out by the manufacturer. In this assessment the effect of the safety features in
the control system will be taken into account when looking at the overall risk of each possible
hazardous event. Standard EN 1050 – Principles for risk assessment – describes the information,
which is necessary for risk assessment.
