Lenze PROFIBU PC-based Automation - Manual (Page 57)

DMS 2.2 EN 07/2011 TD17
L
57
Control technology | PROFIBUS communication manual
Defining the minimum cycle time of the PLC project
Calculating the total access time to the peripheral devices (T
Correction
)
9 Defining the minimum cycle time of the PLC project
This chapter will inform you on how the minimum cycle time of the PLC project can be
defined.
The calculation of the minimum cycle time comprises the following steps:
1. Calculating the total access time T
Correction
to the peripheral devices.
Calculating the total access time to the peripheral devices (T
Correction
)
( 57)
2. Determining the task utilisation T
Task utilisation
of the application during operation.
Detecting the task utilisation of the application (T
Task utilisation
)
( 58)
3. Calculating the minimum cycle time.
Calculating the minimum cycle time
( 60)
4. Optimising the system.
Optimising the system
( 61)
9.1 Calculating the total access time to the peripheral devices (T
Correction
)
The cycle times depend on the number of configured field devices and the IPC hardware
used.
Example
Configuration Access time with processor
ATOM 1.6 GHz
1 PROFIBUS master (logic) 140 μs
1. axis
(16 input words and 16 output words)
40 μs
For each further axis
(16 input words and 16 output words)
10 μs
Access times for an industrial PC (ATOM 1.6 GHz) with 3 axes
Access time of PROFIBUS master
+ access time of 1. axis
+ access time for 2 further axes
140 μs
40 μs
20 μs
= total access time 200 μs