BECKHOFF DK9222-0909-0005 User Manual

XFC

Application Note DK9222-0909-0005

XFC technology oversampling

Oversampling

Keywords

XFC
oversampling
Distributed Clocks
EtherCAT
EL1262
EL2262
EL3632
EL3702
EL3742
EL4712
EL4732

Oversampling is a special type of signal sampling that is used for refining the time resolution of a signal.

Detection of the signal curve is refined according to the set oversample factor, so that high resolutions of

up to 1 µs (digital EL12xx input terminals) and 10 µs (analog EL37xx input terminals) are possible.

Technical background

Oversampling means that a signal is scanned with a higher frequency within the terminal than would be required for the signal

transfer. The time window of the signal variation is narrower than the duration of a communication cycle, since sampling takes

place several times within a communication cycle. In order to maintain the chronology of the events, a whole set of process

data is transferred to the controller during the next communication cycle.

Achieving shorter cycle times via high-performance fieldbus technology and high-performance processors is one technique for

improving the time resolution of the signal curve in the field. Alternatively, the higher precision can be achieved through high-

precision input and output terminals, rather than during data transfer. This technical approach for finer time resolution of the

data requires a reliable time relationship between all system devices to be generated.

For application notes see disclaimer on the last page

Beckhoff

New Automation Technology

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Application Note DK9222-0909-0005

XFC technology oversampling

XFC

Fig. 1 Local clock generators in the field

This is possible through the distributed clock function under EtherCAT (see Fig. 1): The local clock generators in the EtherCAT

slaves provide a uniform system time. The differences in internal protocol run-times of the bus between slaves are calculated,

and these micro-delays are compensated after synchronisation of the clocks in the EtherCAT slaves. The now unified system

time in the bus system allows reliable chronological relationships between different events within the system. For distributed

clock function see distributed clocks system description, available from the download area under http://www.beckhoff.com/

english/download/ethercat.htm .

The precision of the signal acquisition at I/Os is achieved through oversampling of the signal. This means that the signal is not

queried once per communication cycle as usual, but several times with a defined frequency within the cycle. The sampled data

are sent to the controller as a process data packet with the next communication cycle and analysed. For the user this has the

advantage that a finer subdivision can be achieved through oversampling with a typical motion application communication

cycle of 1 ms, without having to modify the cycle time. With an oversample frequency of 10 kHz and a cycle time of 1 ms the

For application notes see disclaimer on the last page

Beckhoff

New Automation Technology

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