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Watch list (
Call tree (
Cycle time
In this chapter a somewhat special subject will be treated. Those to whom it is
important to get a deeper understanding of a PLC, should study it. It can be
skipped. Then continue on page 4-9.
It is assumed that the contents of chapter 1.5 is known.
When to skip?
Two concrete conditions are mentioned here when it is recommended to skip
this chapter:
●
if the processes in the application are not time-critical (
●
Those who are making their first experience with a PLC should study this
chapter later on.
Made on your
For test purposes it may be interesting to measure the processing time for
own
function blocks, networks, combinations of them or program modules yourself.
With some routine it should not be difficult to create such function blocks. Here
we only want to mention some points briefly.
Cycle counter
A cycle timer you have created on your own for the number of processed
program cycles may look like
Figure 125: Cycle counter
This counter is useful if an average value is to be measured from 1,000 cycles.
In some hardware versions there is an internal clock generator with a resolution
Internal clock
of µs. "Reading" is effected with the module 'TIMER_READ_US' from the
hardware-specific library,
generator the module is, of course, not available.
Using this module, very precise measurements are possible. Depending on the
part of the program whose duration is to be determined, the timer command is
used. This can happen twice in the program to start and stop the time. The
difference between these values can be further evaluated. It corresponds to the
individual processing time. It is, for example, possible to calculate the average
or the maximum across 1,000 cycles.
Further processing is left to the reader.
PLC browser
It is necessary, in particular in time-critical processes, to determine the cycle
time. A powerful PLC system such as ecomatmobile supports the user in this
respect. Respective routines are implemented in the operating system. They
have to be activated in the software for programming, CoDeSys. This is done in
the item 'PLC browser' above the tab (of the register card) 'Resources'.
R
page 5-17)
page 5-19)
Figure 22. With hardware versions without clock
Exercises
page 1-7 et seqq)
4-7
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