Distributed Clocks - Leuze electronic DDLS 538 Series Original Operating Instructions

EtherCAT
No EtherCAT slave participant between the data transmission paths
The calculated minimum cycle times of the given used control are doubled (see chapter 7.4.3 "Calculation
of the control cycle time").
E therC A T
1 2
1 Master
2 Bus terminals
Fig. 7.7: Cascading without slave participant between the data transmission paths
7.5

Distributed Clocks

Overview
Spatially distributed processes are synchronized with respect to time using Distributed Clocks (DC).
The time of the first synchronous EtherCAT slave is used as the reference (master clock).
The reference time is sent cyclically to all other slave clocks. These can then adjust themselves exactly to
the reference time one after the next.
The time information is subject to propagation time delays in the EtherCAT network.
Causes of propagation time delays:
• The signal propagation time on the cable
• The signal propagation time through the participants
• The signal propagation time through infrastructure components such as an optical data transceiver
• Variable propagation time delay due to constantly changing transmission distances when using an opti-
cal data transmission system.
Synchronization via DC
• Each DC slave sends the exact time to the DC master at which it received the telegram.
• The DC master stores these times and allows a relative deviation of 2 µs to the measured propagation
time delay.
• EtherCAT is able to constantly recalculate and compensate for the propagation time delays.
The propagation time delay of the EtherCAT network is remeasured by the DC master every 10 s.
Example:
DC-capable slaves with time information can be networked with one another via an optical data transceiver.
One of the two data transmission devices is stationary, the other is installed, e.g., mobile on a stacker
crane.
• At a maximum expected speed of the stacker crane of 10 m/s, this will traverse a distance of 100 m
within 10 s*.
(*: the propagation time delay is remeasured every 10 s)
Leuze electronic GmbH + Co. KG
D D LS 538
D D LS 538
F requency F4 F requency F3
D D LS 538
D D LS 538
F requency F requency F3
F4
D D LS 538
D D LS 538
F requency F4 F requency F3
DDLS 538 ...
S lave
D D LS 538
D D LS 538
F requency F4 F requency F3
D D LS 538
D D LS 538
F requency
F requency F4 F3
S lave
S lave
59