226 PROFIsafe
PROFIsafe watchdog time
F-Parameter F_WD_Time determines the watchdog time for the PROFIsafe
connection. The minimum watchdog time is composed of four timing sections as
shown in this figure.
1. Device acknowledgement time (DAT) is the time it takes for the F-Device (such as
the FSO module) to process an incoming PROFIsafe frame. DAT starts when the
F-Device receives the PROFIsafe frame and ends when the F-Device has
prepared a new PROFIsafe frame using the currently available process values.
2. Bus time is the time it takes when the PROFIsafe frame is transmitted from the
F-Device (FSO module) to the F-Host (such as the ABB SM560-S safety
controller station) through the "black channel".
3. Host acknowledgement time (HAT) is the time it takes for the F-Host to process
an incoming PROFIsafe frame.
4. Another Bus time elapses when the new PROFIsafe frame is transmitted from the
F-Host back to the F-Device.
F_WD_Time assigned to the FSO module must be higher than the minimum
watchdog time. The worst-case delay time of the FSO module also depends on the
safety functions that are used simultaneously and on the PROFIsafe cycle time. The
longest worst-case delay time of the FSO module is 50 ms which is based on its
internal watchdog.
Minimum watchdog time
DAT
HAT
Bus
Bus
1
3
4
Time
2
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