RFC 4072S
38 / 272
PHOENIX CONTACT 108580_en_02
2.3.3 Determining F_WD_Time IN/F_WD_Time OUT to be param-
eterized and checking/validating that the safety function
can be implemented
Having calculated the upper and lower limits of the F_WD_TimeIN/F_WD_TimeOUT as
described in the two previous sections, you now need to determine the F_WD_Ti-
meIN/F_WD_TimeOUT watchdog times that are to be parameterized within these limits for
the safety function that is to be implemented. You then need to check/validate that the
required safety function can be implemented using the determined values.
The values are essentially determined as follows:
The relationship between the values for F_WD_Time IN and F_WD_Time OUT is based on
the relationship for the minimum F_WD_Time and the system availability determined in Sec-
tion 2.3.2 on page 32.
Example Based on the maximum possible safety function response time, the following requirement
must be met:
The watchdog times to be parameterized are chosen as follows in the example:
Factor 2 has been chosen here so that it is still possible to later increase the PROFINET
repeat cycles by the monitor factor or the PROFINET update time without endangering sys-
tem availability by exceeding the F_WD_Time monitoring time.
As a result, the values selected in the example project (see Figure 4-46 on page 123 and
Figure 4-47 on page 124) described in Section 4.3.1 are within the permissible range:
 Sum of the watchdog times is less than 200 ms.
(F_WD_Time IN
min
+ F_WD_Time OUT
min
) < (F_WD_Time IN + F_WD_Time OUT) < (F_WD_Time IN
max
+ F_WD_Time OUT
max
)
F_WD_Time IN
max
+F_WD_TimeOUT
max
=200ms (Upper limit from the safety
function)
F_WD_Time OUT
min
=24.5ms (From the example in
Section 2.3.2)
F_WD_Time IN
min
=50ms (Assumed for the example
calculation)
F_WD_Time OUT ≈ 2x24.5ms  F_WD_Time OUT = 50 ms
F_WD_Time IN = 2 x 50 ms = 100 ms
Minimum F_WD_Time (IN+OUT) < F_WD_Time (IN+OUT) to be parameterized < Maximum F_WD_Time (IN+OUT)
(50 + 24.5) ms
< (100 + 50) ms < 200 ms
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