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:
• Although a PROFIBUS PA
™
system can use the same physi-
cal wiring as an existing 4–20 mA device, fieldbus devices
are not connected point to point, but rather are mul-
tidropped and wired in parallel on a single pair of wires
(referred to as a segment).
• 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
Enhanced Eclipse Model 705PA transmitter is a
PROFIBUS PA
™
certified device that communicates with
the DPV1 protocol operating 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.
4
57-645 Eclipse Guided Wave Radar Transmitter - PROFIBUS PA
™
Control Room
Power Supply
Terminator
6234 feet (1900 meters) maximum
PC
Terminator
P
ower
Conditioner
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