Question:
When the STO function is enabled, an error message is indicated at the safe Beckhoff output terminals although the wiring is free from errors. What is the reason for this?
Answer:
The two input circuits of the STO modules contain capacitances to ensure that the clock pulses of OSSD outputs will not inhibit the controller for a short time. With some Beckhoff output terminals, the high current flow occurring when the capacitances are loaded when enabling the module lead to misleading error messages (short circuit).
This behaviour can e. g. be avoided by using a resistor (27 Ohm, 1 W) or an inductor in the GI cable (ground of the safe input) to limit the inrush current.
