Technical Manual
WDGA with EtherCAT
3 - Description of the equipment
© Wachendorff Automation GmbH & Co. KG
8
Rev.1.09
The focal areas of EtherCAT's development were short cycle tim
es (≤ 100 µs), low jitter
for precise synchronisation (≤ 1 µs) and low hardware costs.
The telegram sent by the EtherCAT master runs through all network members. Every
EtherCAT slave reads the output data addressed to it and places its input data in the
forwarded data frame while the telegram is passing through the device. The telegram
is only delayed by hardware cycle times. The last member in a segment (or branch)
detects an open port and sends the telegram back to the master. The full duplex
capability of Ethernet is used for this.
The maximum user data rate of a telegram is over 90%, while the theoretical effective
data rate from the use of the full duplex capability is in excess of 100 Mbit/s (> 90% of
two x 100 Mbit/s).
The EtherCAT master is the only member in the segment that can actively send an
EtherCAT frame; all other members simply pass the frames on. This avoids
unexpected delays and guarantees real-time compatibility.
The master uses a standard Ethernet medium access controller (MAC) without an
additional communication processor. This means that a master can be installed on any
hardware platform that provides an Ethernet port. The EtherCAT slaves use an
EtherCAT slave controller (ESC) for processing in the cycle that is handled entirely in
hardware. This means that network performance can be predicted and is independent
of the individual slave device implementation.
[EtherCAT Technology Group,
www.ethercat.org, 2017]
Further information on EtherCAT can be found on the EtherCAT Technology Group's
website at:
3.3 Principles of WDGA
The sections below describe the basic functions on absolute encoder.
Unlike incremental encoders, absolute encoders output their position value as a digital
number via a field bus. A distinction is made between single-turn and multi-turn
encoders.
In addition to the simple output of the position value, most encoders also allow a certain
degree of parametrisation, such as the choice of positive direction of revolution, the
setting of the position value to a reference value at a defined physical position and
scaling of the position value to a desired resolution and a limited measuring range. As
a result, the amount of development work required in the control program is reduced,
and the computing capacity of the control unit is relieved.
Summary of Contents for WDGA Series
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