NORD Drivesystems BU0530 - Manual (Page 22)

Functional safety with NORD SK 500E frequency inverters
22 BU 0530 GB-3712
2.2 Safety functions
A stop function can be executed by means of a safe shut-down method. As this has priority over other control
functions this stop-function is suitable for stopping in emergencies. This ensures that the torque is shut down
by means of a safe shut-down method. This function is known as "safe torque off" or STO.
It is also possible to first stop the motor in a controlled manner and then to switch off the torque. This function
is referred to as "safe stop 1" or SS1.
2.2.1 Safe torque off, STO
With the STO function the drive torque is switched off as quickly as possible (see Technical Data  Reaction
Time) and the drive until (motor and machine) run down to a standstill. This behaviour corresponds to Stop
Category 0 (uncontrolled braking) as per EN 60204-1. A certain time therefore elapses until the drive unit does
not perform any further dangerous movements and a safe state is achieved. Monitoring of whether or when the
drive unit has achieved a safe state is not integrated into the frequency inverter.
According to the switching equipment used and with the use of a safe shut-down method, an STO function with
Safety Category 4 as per DIN EN ISO 13849-1 can be implemented.
NOTE Control of a mechanical brake by means of the inverter is not fail-safe!
A mechanical brake connected to terminals 1 (K1.1) and 2 (K1.2) can be applied on triggering
of the STO function. This means that in this case, the brake must be designed as an operating
brake, as the drive unit and all of its rotating mass is stopped by the mechanical brake.
Slippage of lifting gear when triggering the STO function must be prevented by suitable brakes
where necessary!
2.2.2 Safe stop 1, SS1
With the SS1 function, the motor is first stopped by the inverter and after standstill the device switches to the
STO function. This method is the same as stop category 1 (controlled stop) as per IEC60204-1. Switching to
the STO function can be monitored after reaching standstill or can be carried out via a fail-safe timing relay
(delayed output of a protective switching device).
NOTE
Controlled braking is triggered via a digital input and only complies with low safety requirements!
If controlled braking fails then the device switches over to STO.
If necessary, the braking process must be monitored.
NOTE
Control of a mechanical brake by means of the inverter is not fail-safe!
In case of failure of controlled braking, a mechanical brake connected to terminals 1 (K1.1) and
2 (K1.2) may be overloaded, as this brake is applied when the STO function is triggered.
If necessary, slippage of lifting gear must be prevented by the use of suitable brakes.