Siemens SIMATIC S5-90U, Системное руководство

Страница: 141 / 622

S5-90U/S5-95U Addressing and Access to I/Os
Calculating the Scan Time
The scan time includes the following:
•
Process image transfer time
• Operating system runtime
• Program execution time
• Execution time for internal timers
Example: Your S5-95U configuration includes an IP 266 and an IP 267. All analog channels of
the onboard I/Os are to be read into the PII. The program execution time for your
control program is 4000
µs
(=4 ms). You have parameterized 10 timers since your
control program processes timers T0 to T9.
How long is the scan time?
1. Process image transfer time:
PI transfer time of the onboard I/Os =8·80 µ s=640 µ s
PI transfer time of the external I/Os =(64+32)·34 µ s=3264 µ s
The process image transfer time is thus 640 µ s+3264 µ s=3904 µ s 3.9 ms
2. Operating system runtime:
The operating system runtime is 500
µ
s=0.5 ms
3. Program execution time:
The program execution time is 4000
µ s=4 ms.
4. Execution time for internal timers:
A single updating cycle for the 10 timers takes t
T
=10·33 µ s=330 µ s.
Add the operating system runtime, process image transfer time and program execution time,
i. e. t
x
=0.5 ms+3.9 ms+4 ms=8.4 ms, to obtain the interval. The execution time for the
internal timers is to be added to this interval.
Hence:
Execution time for internal timers= (1+ )
•
330 µ s=607.2 µ s 0.6 ms
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
a a a a a a a a a a
8,4 ms
10 ms
5. Scan time:
The scan time is the sum of all times calculated under 1 to 4.
Scan time =0.5 ms+3.9 ms+4 ms+0.6 ms= 9 ms
EWA 4NEB 812 6115-02b
6-21