Description of the RFC 4072S
108580_en_02 PHOENIX CONTACT 29 / 272
2.3.1 Determining SFRT
max
and
F_WD_Time IN
max
/F_WD_Time OUT
max
In the application, the maximum permissible SFRT must be determined for each safety func-
tion implemented in the application. This maximum permissible SFRT also includes the part
of the SFRT that applies to the PROFIsafe system if PROFIsafe and the RFC 4072S are
involved in the safety function.
A method of calculation for determining the part of the SFRT that applies to PROFIsafe is
specified in the PROFIsafe system description (see Figure 2-2). The method of calculation
specified is subject to certain general conditions.
Figure 2-2 Calculation of the SFRT response time
( *) = Not necessarily the output device
The TWCDT (total worst case delay time) is therefore the sum of all maximum signal run-
times that may occur in the individual elements during normal operation.
The individual elements are:
–(PROFIsafe) F-Devices
– Transmission (PROFIsafe via PROFINET including all network infrastructure compo-
nents and lower-level subsystems, e.g., Inline/Axioline F local bus)
– iSPNS 3000
Due to a closely synchronized sequence of F-Host/iSPNS 3000 processing, this model is
simplified when using the RFC 4072S. The runtimes, cycle times, and watchdog times of
the iSPNS 3000 (processing delay and F-Host_WD) are not actually relevant when deter-
mining the SFRT.
For detailed information regarding the PROFIsafe system description, please refer to
Section “Documentation” on page 232.
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