Rockwell Automation 1757-FFLD Linking Device Configuration Manual - Manual (Page 24)

Publication 1757-PM002A-EN-E - June 2006
2-14 Set Up A System
Figure 2.8 Proper Shielding for a Tree Network
Signal Quality
When a fieldbus network’s signal quality is poor, it can cause intermittent loss
of communication to devices, unreasonably long downloads, and lost data. The
following components are critical to achieving good signal quality:
• Shielded two wire cable, preferably specifically designed for fieldbus.
The type of cable will determine overall length of the trunks and drops.
• Terminators. Terminators reduce noise on segments caused by signal
reflections at the end of an open cable. One terminator on each end of
the H1 trunk is needed for proper performance.
• Power conditioners are mandatory between a supply and the H1 trunk,
which can deliver 9-32 V DC consistently out of the conditioner when
under the appropriate load from the cable resistance and while powering
the devices. One power supply, or redundant power supplies designed
for fieldbus, can be used.
• In areas vulnerable to lightning, lightning arresters should be installed.
The four issues above along with proper shielding and grounding will ensure
proper signal qualities.
T T
FFLD
All Shields
Tied Here
F
F
F