Siemens Simatic S7-300 CPU 31xC and CPU 31x S7-300 User Manual

Page 101

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Cycle and reaction times

5.4 Calculating method for calculating the cycle/response time

CPU 31xC and CPU 31x, Technical data
Manual, Edition 08/2004, A5E00105475-05

5-19

5.4

Calculating method for calculating the cycle/response time

Introduction

This section gives you an overview of how to calculate the cycle/response time.

Cycle time

1. Determine the user program runtime with the help of the

Instruction list.

2. Multiply the calculated value by the CPU-specific factor from the table

Extension of user

program processing time.

3. Calculate and add the process image transfer time. Corresponding guide values are

found in table

Data for calculating process image transfer time.

4. Add the processing time at the scan cycle checkpoint. Corresponding guide values are

found in the table

Operating system processing time at the scan cycle checkpoint.

5. Include the extensions as a result of testing and commissioning functions as well as

cyclical PROFINET interconnections in your calculation. These values are found in the

table

Cycle time extension due to testing and commissioning functions. The final result is

the cycle time.

Extension of the cycle time as a result of interrupts and communication load

100 / (100 – configured communication load in %)
1. Multiply the cycle time by the factor as in the formula above.
2. Calculate the runtime of interrupt processing program sections with the help of the

instruction list. Add the corresponding value from the table below

3. Multiply both values by the CPU-specific extension factor of the user program processing

time.

4. Add the value of the interrupt-processing program sequences to the theoretical cycle

time, multiplied by the number of triggering (or expected) interrupt events within the cycle

time. The result is an approximation of the physical cycle time. Note down the result.