Settings in TwinCAT 2.11

External synchronization via EtherCAT is supported from TwinCAT 2.11. The synchronization direction can be set in the associated dialog.

Distributed clock timing settings

Fig. Synchronization direction shows the synchronization direction for the respective synchronization type, i.e. the source on which the synchronization time is based.

• Independent DC Time (A):
  One of the EL terminals (generally the first terminal supporting distributed clocks (DC)) is the reference clock to which all other DC terminals are adjusted. Selection of the reference clock in the dialog above.
• DC Time controlled by TwinCAT (B):
  The DC reference clock is adjusted to the local TwinCAT time. This setting is used in cases where several EtherCAT systems with distributed clocks function are operated in the same control system. This tracking mode is less accurate.
  If high accuracy is required the external CU2508 EtherCAT distributor must be used.
  Note: In the subordinate EtherCAT system a device without firmware intelligence (e.g. an EK1100 coupler) must be set as ReferenceClock.
  Please refer to section “Coupling of EtherCAT systems”.
• DC Time controlled by External Sync Device (C):
  If the EtherCAT system is to be adjusted to a higher-level clock, the external sync device can be selected here.
  Please refer to section "External synchronization".

Process data settings

TwinCAT 2.11 can display the current offsets in [ns] in the EtherCAT master info data.

• These offsets are calculated once after EtherCAT has started.
• The synchronization control keeps these offsets constant.
• If local DC time values in the synchronized EtherCAT system are to be related to the absolute reference from the higher-level EtherCAT system (e.g. from EL1252 timestamp terminals), the user must adjust this offset with each local timestamp.

Sample: t_{EL1252 timestamp channel 1, absolute time} = t_{EL1252 timestamp channel 1, local DC time} + t_{ExtToDcOffset} + t_TcToDcOffset