Emerson AMS Trex Device Communicator User Manual page 103

User Guide
3.18.4
User Guide
1.800.561.8187
Figure 3-40: Connect to an externally-powered FOUNDATION fieldbus device
For small fieldbus segments, the power conditioner and terminators can be contained in a
single wiring block.
Note
You can connect the Trex unit at any convenient place along the fieldbus segment (bus). In
the field, this is typically done at the device or at the fieldbus junction box. The drawing
below is one example.
A. Terminators
B. Power conditioner
C. Fieldbus power supply
D. Host system
Related information
FOUNDATION fieldbus communication terminals
Power and connect to a FOUNDATION fieldbus device
Connect to an externally-powered FOUNDATION fieldbus device
Link Active Scheduler (LAS)
All fieldbus segments have only one Link Active Scheduler (LAS). The LAS operates as the
bus arbiter for the segment. The Trex unit is the last node to become the LAS on a fieldbus
segment.
The devices that can be the LAS are called link master devices. All other devices are called
basic devices. Use the Trex unit to set a device to be a link master or basic device.
When a fieldbus segment first starts up, or upon failure of the existing LAS, the link master
devices on the segment bid to become the LAS. The link master with the lowest address
begins operating as the LAS immediately after completing the bidding process. Link
masters that do not become the LAS can act as LAS backups by monitoring the fieldbus
segment for failure of the LAS and then bidding to become the LAS when a LAS failure is
detected.
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September 2021
103