4
BE 57-658 Eclipse
®
Model 706 Guided Wave Radar Transmitter – PROFIBUS PA output
1.0 PROFIBUS PA
™
Overview
1.1 Description
PROFIBUS PA
™
is a digital communications system that
serially interconnects devices in the field. A fieldbus system
is similar to a Distributed Control System (DCS) with two
exceptions:
• PROFIBUS PA
™
is a system that allows the user to
distribute control across a network. Fieldbus devices are
smart and actually maintain control over the system.
Unlike 4–20 mA analog installations in which the two wires
carry a single variable (the varying 4–20 mA current), a dig-
ital communications scheme such as PROFIBUS PA
™
con-
siders the two wires as a network. The network can carry
many process variables as well as other information. The
Model 706PA transmitter is a PROFIBUS PA
™
certified
device that communicates with the DPV1 protocol operat-
ing at 31.25 kbits/sec. The MBP physical layer is an
approved IEC 61158 standard.
An IEC61158 shielded twisted pair wire segment can be as
long as 6234 feet (1900 meters) without a repeater. Up to
4 repeaters per segment can be used to extend the distance.
The maximum number of devices allowed on a fieldbus seg-
ment is 32 although this depends on the current draw
of the devices on any given segment.
Details regarding cable specifications, grounding, termination,
and other network information can be found in IEC 61158
or the technical guideline “PROFIBUS PA
™
User and
Installation Guideline” at www.profibus.com.
Control Room
P
ower Supply
Ter mi na t or
6
234 feet (1900 meters) maximum
P
C
Ter mi na t or
P
ower
Conditioner
Typical PROFIBUS Installation
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