Siemens SIMATIC S5-90U System Manual page 142

Addressing and Access to I/Os
Calculating the Response time
The response time includes the following:
• 3 x process image transfer time+
• 3 x operating system runtime+
• 2 x program execution time+
• Execution time for internal timers+
• Input delays
Example: Your S5-95U configuration includes a 16-channel digital input module, an IP 266 and
an IP 267. Four analog channels of the onboard I/Os are to be read into the PII. The
time required for executing the control program is 5000 µs (=5 ms). You have
parameterized 20 timers since your control program processes timers T0 to T19.
Determine the (longest possible) response time.
1. Process image transfer time:
PI transfer time of the onboard I/Os =4·80 µs =320 µs
PI transfer time of the external I/Os =(16+64+32)·34 µs =3808 µs
The process image transfer time is thus 320 µs+3808 µs= 4128 µs 4.1 ms
2. Operating system runtime:
The operating system runtime is 500 µs =0.5 ms
3. Program execution time:
The program execution time is 5000 µs=5 ms
4. Execution time for internal timers:
A single updating cycle for 20 timers takes t
Add 3 x process image transfer time, 3 x operating system runtime and 2 x program execution
time, i.e. t =3·4.1 ms + 3·0.5 ms + 2·5 ms=23.8 ms, to obtain the interval.
X
The execution time for the internal timers is to be added to this interval.
Hence:
Execution time for internal timers =
5. Input Delays
The input delays for the S5-95U are typically 2.5 ms; the typical input delay for the 16-channel
input module is 4 ms. The 4 ms delay will be used for subsequent calculations.
6. Response time
The response time results from the addition of all times calculated under points 1 to 5.
Response time =3·4.1 ms+3·0.5 ms+2·5 ms+2.2 ms+4 ms=30 ms
6-22
=20·33 µs =660 µs.
T
23.8 ms
(1+ ) 660 µs=2230.8 µs 2.2 ms
•
10 ms
S5-90U/S5-95U
EWA 4NEB 812 6115-02b