SIRIUS®
Weak points of standard EtherCAT®:
Master sends the empty message train
i.e. when DEWESoft® is the master and does not send the empty message for some reason, there will be no
data on the bus
Real time performance required from computer
No data-buffer on the devices
Ethernet packet (no TCP/IP) is prone to data-loss
Time synchronisation is mostly done based on master precision of sending messages
→ this makes standard EtherCAT® good for real-time application, but not good for data-acquisition.
Since the standard EtherCAT® is originally intended for real time, it lacks few very important elements. This is why
DEWESoft®uses an enhanced DS-EtherCAT+ protocol:
5.1.2.2 DS-EtherCAT+
In comparison to standard EtherCAT® the DS-EtherCAT+ protocol has following benefits:
Buffering: DEWESoft® EtherCAT® devices buffer the measurement data for some seconds, so that all data
can still be accessed, even if the Master (i.e. DEWESoft® on Windows®) is a little late.
Synchronisation: DEWESoft® EtherCAT® devices can acquire the samples at an exact time stamp. The
timestamp can be provided by an external timing source (e.g. GPS or IRIG)
Retransmit: since EtherCAT® packets are below the TCP/IP level, the standard protocol does not handle lost
packets. The enhanced DS-EtherCAT+ protocol will detect lost packets and retransmit them.
Notes:
Since the SIRIUS® devices are EtherCAT® slaves, an external EtherCAT® master is required
EtherCAT® needs a dedicated network interface: i.e. you cannot mix EtherCAT® to your existing Intranet
(LAN network) or Internet1 (i.e. connect them to the same Ethernet-switch)
In comparison to the SIRIUS-USB slices, the SIRIUS EtherCAT® modules do not have CAN and no analogue
output
HINT
The maximum number of samples per device using EtherCAT® bus is 160 kS/sec for all
transmitted channels: i.e. for 8 channels the rate would be 20 kHz.
The maximum speed per bus is limited to the 100 Mbit EtherCAT® bus speed.
When DEWESoft® is the master, it can utilize approximatively half of this bandwidth, but
other masters might be more efficient.
5.1.2.3 EtherCAT® specifications
Max. Sample Rate ADC Type
8
20kS/sec (Dual Core), 10kS/sec (High Density)
Note: High-speed modules are NOT supported.
Max. Throughput per slice 640 kByte/sec (=160kS/sec total rate)
Max. Throughput per chain 3200 kByte/sec (=800kS/sec total rate)
Max. distance between slices 75 meters
9
Max. number of slices
10
100 (additional power injectors required)
Connector type Lemo 1B 8 pin (Data and power supply)
8 The data rate decreases when you activate counter channels (8 Byte per counter channel)
9 The distance can easily be increased by using fiber optics instead of standard Ethernet cables
10 When the max. allowed current and supply voltage dropout is reached, you must add power injectors
Page 48/166 www.dewesoft.com Doc-Version: 1.4.2
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