PROFINET Forum

The PROFIsafe Profile states in section 'Adjustment of watchdog times for FSCP 3/1':

It is highly recommended that the difference between the assigned parameter value F_WD_Time and the sum (DAT, HAT, and bus transmission delays) does not exceed 30 %.

Why is this the case?

PS-cE wrote: ↑21 Nov 2024, 15:29 The PROFIsafe Profile states in section 'Adjustment of watchdog times for FSCP 3/1':

It is highly recommended that the difference between the assigned parameter value F_WD_Time and the sum (DAT, HAT, and bus transmission delays) does not exceed 30 %.

Why is this the case?

In section 'Calculation and optimization', the formula for calculating the Safety Function Response Time (SFRT) part for PROFIsafe is given. The F_WD_Time is part of this calculation. The underlying model assumes the F_WD_Time to be within the stated 130% limit, otherwise the SFRT formula would not work anymore/would have to be adapted.