Description of the RFC 4072S
108580_en_02 PHOENIX CONTACT 31 / 272
The central component in Figure 2-3 on page 30 is deemed to be the sum of
F_WD_Time IN
max
and F_WD_Time OUT
max
.
The sum of these times specifies the maximum internal processing time that is required for
point-to-point communication via PROFIsafe between the PROFIsafe input device and the
PROFIsafe output device using the iSPNS 3000 in the RFC 4072S, even in the event of an
error, such as a telegram delay.
The actual SFRT to be implemented for the PROFIsafe system can be determined accord-
ing to the following equation:
Take into consideration all the links that are involved in the safety function and programmed
in the safety-related application program.
Always take into consideration all the links that are involved in the safety function and pro-
grammed in the safety-related application program.
Maximum permissible
watchdog times
To incorporate the maximum permissible watchdog times
F_WD_Time IN
max
/F_WD_Time OUT
max
in the PROFIsafe system, the following equation
should be used:
WCDT OUT Worst case delay time of the F-Device with output function.
For this time, please refer to the device-specific user documen-
tation for the F-Device used.
Device WD Internal watchdog time of the F-Device involved in the safety
function.
SFRT = WCDT IN + (F_WD_Time IN
max
+ F_WD_Time OUT
max
) + WCDT OUT [1]
SFRT must therefore be ≤ SFRT
max
F_WD_Time IN
max
+ F_WD_Time OUT
max
≤ SFRT
max
- WCDT IN - WCDT OUT [2]
Please refer to the F-Device-specific user documentation to check whether further infor-
mation is available regarding watchdog times within the internal device function.
If F-Devices are used where there is a difference (ï…„ t) between their worst case delay time
(WCDT) and the implemented device watchdog time (Device WD), this difference must
be taken into consideration in accordance with the PROFIsafe model for determining the
SFRT.
Timer functions that are used within the safety function in the safety-related application
program must be taken into consideration.
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