Lenze PROFIBUS Controller-based Automation User Manual
Page 45
Lenze · Controller-based Automation · PROFIBUS® Communication Manual · DMS 4.3 EN · 04/2014 · TD17
45
9
Defining the minimum cycle time of the PLC project
9.1
Determining the task utilisation of the application
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How to determine the task utilisation:
Initial situation: A complete project, e.g. with a PROFIBUS task and 2 lower priority tasks
has been created.
1. For a first measurement of the task utilisation, set the cycle times of all cyclic tasks
available in the PLC system "high" (e.g. PROFIBUS task = 10 ms, all other cyclic
tasks = 20 ms).
2. Use the menu command Online Login, or log in on the Lenze Controller with
• For this, the PLC program must be error-free.
• With the log-in, the fieldbus configuration and the PLC program are loaded into the
Controller.
3. Reset the values displayed on the Monitor tab of the Task Configuration to 0 after the
complete run-up of the system.
Execute the Reset command from the context menu of the task name field.
4. Read the displayed maximum computing time of the task with the highest priority.
In the illustration above, the max. cycle time of the PROFIBUS task is 647 μs.
The minimum cycle time (T
min
) for a system can be calculated by means of the formula:
T
min
= Task utilisation x safety factor
Note!
A safety factor of 1.5 should be included in the calculation.