Response Times And Minimum Signal Duration For Ob3 Interrupts - Siemens SIMATIC S5-95F Manual

S5-95F

18.12.4 Response Times and Minimum Signal Duration for OB3 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 basic unit. Not included in the
interrupt response time are the delays caused by circuits, sensors and actuators.
Interrupt Response Time for OB3 Interrupts
The interrupt response time for OB3 interrupts T
• The S5-95F's internal delay for OB3 interrupts (max. 12 ms if you do not process OB2 interrupts
and max. 16 ms if you process both OB2 and OB3 interrupts)
• Execution time T
OB2
• Execution time T
OB3
• Number of interrupt input bytes n
In the majority of applications, the programs in OB2 and OB3 are relatively short. The execution time
of OB2 is generally less than 0.2 ms and that of OB3 less than 10 ms. You can therefore expect a
typical interrupt response time of 23 ms for OB3 interrupts.
If the execution times of OB2 and OB3 for your application differ from those assumed above, you
can calculate the interrupt response time using the following formulae.
Interrupt Response Time for OB3 Interrupts under Worst-Case Conditions
(OB3 Interrupts only)
Under worst-case conditions, the response time for OB3 interrupts if no OB2 interrupts are
used is
T
OB3 response, wort-case
Interrupt Response Time for OB3 Interrupts under Worst-Case Conditions
(OB2 and OB3 interrupts)
Under worst-case conditions, the response time for OB3 interrupts when OB2 interrupts are
also used is
T
OB3 response, worst-case
Minimum Signal Duration for OB3 Interrupts
Note
An OB3 interrupt is triggered by an edge at an OB3 interrupt input or when the
comparison value of an onboard counter is reached.
The S5-95F detects an edge at an OB3 interrupt input under worst-case conditions
when the signal states "0" and "1" have a duration of at least (5 ms + T
in the case of counters, signal levels "0" and "1" must have a minimum duration of
1.4 ms . For these reasons, be sure to use suitable sensors and keep the OB3 runtime
to a minimum.
EWA 4NEB 812 6210-02
for organization block OB2
for organization block OB3
used for processing OB3 interrupts
bytes
12 ms+1.25×T +1.5 ms×n
OB3
= 16 ms+5×T +1.25×T
OB2
Rules for Failsafe Operation of an S5-95F
depends on:
OB3 response
bytes
+1.5 ms×n
OB3 bytes
(n =1, 2 or 3)
bytes
(n =1, 2, 3)
bytes
);
OB3 response
18-25