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Rules for Failsafe Operation of an S5-95F
18.12.3 Response Times and Minimum Signal Duration for OB2 Interrupts
The interrupt response time is the time between an edge change at the terminals of an interrupt
input and the signal change at the terminals of an output on the base unit. Not included in the
interrupt response time are the delays caused by circuits, sensors and actuators.
Interrupt Response Time for OB2 Interrupts
The interrupt response time for OB2 interrupts T
•
the S5-95F's internal delay for OB2 interrupts (max. 5.6 ms, typ. 3 ms)
•
execution time T
OB2
In the majority of applications, the programs in OB2 are relatively short and the execution time of
OB2 is less than 0.2 ms. You can expect a typical interrupt response time of 3.2 ms for OB2
interrupts.
If the execution time of OB2 for your application differs from that assumed above, you can calculate
the interrupt response time using the following formulae.
Typical Interrupt Response Time for OB2 Interrupts
If you have not disabled an interrupt (IA/RA operations) in the user program, the typical
interrupt response time is calculated as follows:
T
OB2 response, typical
If you disable an interrupt in the user program, the interrupt response time will be extended by
the execution time of the program sequence for which the interrupt is disabled (max. 5 ms).
Interrupt Response Time for OB2 Interrupts under Worst-Case Conditions
If you have not disabled an interrupt in the user program (IA/RA operations), the interrupt
response time under worst-case conditions is calculated as follows:
T
OB2 response, worst-case
If you disable an interrupt in the user program, the interrupt response time will be extended by
the execution time of the program sequence for which the interrupt is disabled (max. 5 ms).
Minimum Signal Duration for OB2 Interrupts
Note
An OB2 interrupt is triggered by a negative edge at an OB2 interrupt input. The S5-95F
detects the edge under worst-case conditions only when signal levels "0" and "1" have
a duration of at least 4 ms . For this reason, be sure to use suitable sensors (no fleeting
contacts or chattering switches).
18-24
of organization block OB2
3 ms+T
OB2
5.6 ms+T
OB2
depends on:
OB2 response
S5-95F
EWA 4NEB 812 6210-02
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