BECKHOFF DK9222-0211-0021 User Manual

I/O

Application Note DK9222-0211-0021

XFC

Keywords

EL1252
EL2212
EL2252
Time stamp
XFC
EtherCAT
Exact system time
eXtreme Fast Control
Process data

Time stamp – a snapshot of control technology

This application example describes how, using the Beckhoff XFC technology, the temporal resolution of

field signals for the controller is made several times more precise and, in addition, the validity of the

process data is released from the PLC cycle. The bases for these characteristics are the fast real-time

fieldbus EtherCAT and the time stamping features of the Beckhoff EL1252 and EL2252 digital input and

output terminals, whose process data contain the exact time specification of an event in addition to the

user data.

Introduction: XFC – eXtreme Fast Control

XFC is a control technology that enables very fast and highly deterministic I/O responses. It includes all hardware and software

components involved in control applications:

– optimized I/Os that can pick up signals with high accuracy or

– EtherCAT as an extremely fast communication network,

– high-performance Industrial PCs as the basis for the control hardware

– TwinCAT, the automation software that links all system components with one another.

Contrary to the original free-running communication links, in which the determinism of the process signals was accordingly

initiate tasks,

inaccurate, the employment of XFC significantly lowers the cycle time and the determinism required for rigorous

real-time demands. XFC enables cycle times of 100 μs without sacrificing the centralized intelligence and its high-performance

algorithms. XFC also includes additional technologies that not only improve cycle times but also temporal accuracy and

resolution. This opens up new possibilities to improve the quality of machines and to shorten reaction times. Measuring tasks,

such as preventive maintenance, the monitoring of life cycles or the documentation of parts quality, can all be integrated

For application notes see disclaimer on the last page

New Automation TechnologyBeckhoff

1

I/O

cycle time

task task

synchronous operation of PLC and fieldbus

I/O update per fieldbus

PLC

point

real-time

cycle time used = maximum resolution of an event

time

time

Application Note DK9222-0211-0021

XFC

in a simple manner in a central place in the machine controller without requiring external black boxes. XFC technology is

completely compatible to existing solutions in all areas and can be used simultaneously on the same hardware and software

platform as other control processes such as PLC and motion control, for example.

Validity of process data

Each PLC-based controller works cyclically: it communicates with its environment by receiving input data, processing these on

the basis of the calculation specification (’program’) and then outputting them to the field as output data. Ideally, the fieldbus

cycle can be executed so quickly that refreshed input data are already present at the beginning of the next program cycle.

Depending on the requirements, these cycle times vary between 50 µs to over 100 ms, and are dependent on the fieldbus used

and the performance of the controller. Independent of the PLC cycle time, the cycle time of the fieldbus must also be taken into

account: Not every fieldbus technology available on the market permits synchronous operation of the PLC and fieldbus with

low cycle times, so that a further temporal inaccuracy can also arise here.

Fig. 1 Synchronous operation

Due to this cyclic orientation, however, an event that occurs in reality at a certain, singular point in time can only be assigned

temporally by the PLC in a certain pattern, i.e. the length of the cycle time. If the controller works, for example, with a cycle

time of 10 ms, the edge change at the read-in input actually took place ’sometime’ within the preceding 10 ms before the I/O

update. A more exact assignment than the cycle time resolution of 10 ms is not possible.

Fig. 2 Temporal relation

For application notes see disclaimer on the last page

New Automation TechnologyBeckhoff

2