ABB FSPS-21 - Calculating the Watchdog Time; Profisafe Watchdog Time

SFRT = Device_WD1 + 0.5 x F_WD_Time1 + F_Host_WD + 0.5 x F_WD_Time2 +
Device_WD2 + Longest ΔT_WD
= 76.5 + 15 + 6 + 25 + 10 + 25 = 159.5 ms
where
• Device_WD1 = 76.5 ms
• F_WD_Time1 = 30 ms
• F_Host_WD = 6 ms
• F_WD_Time2 = 50 ms
• Device_WD2 = 10 ms
• Longest ΔT_WD = Max (0.5 x F_WD_Time1; 0.5 x F_WD_Time2) = 25 ms (all other
used WCDT values are equal to their corresponding watchdog times).
￭ 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.
186 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
PROFIsafe_watchdog_time.pdf
1. Device acknowledgement time (DAT) is the time it takes for the F-Device (such as the
FSPS-21 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
(FSPS-21 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 FSPS-21 module must be higher than the minimum watchdog
time. The worst case delay time of the FSPS-21 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 FSPS-21 module is 10 ms.
Calculating the watchdog time
It is not always easy to calculate the worst case delay time of "black channel" components.
See AC500-S Safety User Manual (3ADR025091M0202 [English]) for a proposed method
of tracing the actual PROFIsafe cycle times in a real system.
You must then set F_WD_Time about 30% higher than the worst case value in variable
tResponseTimeMS (in the AC500-S safety program) for the given safety device.
PROFIsafe 123