STO FUNCTION
APPLICATION MANUAL
SINUS PENTA
PENTA MARINE
IRIS BLUE
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Figure 5 - Example schematic diagram of STO function with Safety Relay PILZ PNOZ X3 for safe
power cut off
The circuit operation is described below.
Start/Stop command is obtained through special-purpose push-buttons.
When the STO command circuit is activated, for the Safety Relay PILZ PNOZ X3:
Input circuits S21-S22 and S31-S32 are open.
Instantaneous output contacts 13-14 and 23-24 will be opened.
At the same time, the
‘Safe Torque Off’ function is activated for the drive, because ENABLE-A (pin 15)
end ENABLE-B (pin S) are de-energized, and consequently the output voltage to the motor is removed.
The motor will be stopped in free-run and the time taken to come to a complete stop will depend on the
load inertia.
The Safety Relay will be reset when, after deactivating the
‘Emergency Stop’, the ‘RESET’ push-button is
pressed: in this case, 13-14 and 23-24 are closed and 24Vdc power supply is restored to the ENABLE-A
and ENABLE-B inputs of the drive.
The ‘Safe Torque Off’ function is deactivated in the Drive and the output voltage to the motor is restored.
The motor will start when receiving the start command through the ‘START’ push-button.
The output relay contacts of the drive can be programmed with one of the software functions available for
remote signalling, including the input Enable Drive status. Being the output relay circuitry based on a
single hardware channel, and being the activation function software programmable by the user, it cannot
be considered as a safe status indication. Therefore, the confirmation that the STO function is active
cannot be safely obtained from the output relay contact of the drive.
Figure 6 shows a simpler example where both ENABLE-A and ENABLE-B are directly controlled by a two-
contact emergency switch.
