Examples Of Calculating The Cycle And Response Times - Siemens SIMATIC PCS 7 CPU 410-5H System Manual

Supplementary information
15.15 Cycle and response times of the CPU 410-5H
15.15.6

Examples of calculating the cycle and response times

Example I
You have installed an S7-400 with the following modules in the central controller:
● a CPU 410–5H in redundant mode
● 2 digital input modules SM 421; DI 32xDC 24 V (each with 4 bytes in the PI)
● 2 digital output modules SM 422; DO 32xDC 24 V/0.5 (each with 4 bytes in the PI)
User program
According to the instruction list, the user program runtime is 15 ms.
Calculating the cycle time
The cycle time for the example results from the following times:
● As the CPU-specific factor is 1.2, the user program execution time is:
● Process image transfer time (4 double-word accesses)
● OS execution time at the scan cycle checkpoint:
The total of the listed times is equivalent to the cycle time:
Cycle time = 18.0 ms + 0.109 ms + 0.31 ms = 18.419 ms.
Calculation of the actual cycle time
● Allowance for communication load (default value: 20%):
● There is no interrupt processing.
So the actual, cycle time is approx. 23 ms.
Calculating the longest response time
● Longest response time
● The delay of the inputs and outputs is negligible.
● All the components are plugged into the central controller; DP cycle times do not
therefore have to be taken into account.
● There is no interrupt processing.
So the longest, rounded up response time is = 46.1 ms.
314
approx. 18.0 ms
Process image: 9 µs + 4 ×25 µs = approx. 0.109 ms
approx. 0.31 ms
18.419 ms * 100 / (100–20) = 23.024 ms.
23.024 ms * 2 = 46.048 ms.
CPU 410-5H Process Automation
System Manual, 09/2014, A5E31622160-AB