1.0 FOUNDATION fieldbus
™
Overview
1.1 Description
F
OUNDATION fieldbus
™
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 F
OUNDATION fieldbus
™
system can use the same
physical wiring as an existing 4–20 mA device, Fieldbus
devices are not connected point to point, but rather are
multidropped and wired in parallel on a single pair of wires
(referred to as a segment).
•F
OUNDATION fieldbus
™
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 digi-
tal communications scheme such as F
OUNDATION fieldbus
™
considers the two wires as a network. The network can carry
many process variables as well as other information. The
Enhanced Eclipse Model 705FF transmitter is a
F
OUNDATION fieldbus
™
registered device that communicates
with the H1 F
OUNDATION fieldbus
™
protocol operating at
31.25 kbits/sec. The H1 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
segment is 32 although this depends on the current draw
of the devices on any given segment.
4
57-640 Eclipse Guided Wave Radar Transmitter - FOUNDATION fieldbus
™
Control Room
Power Supply
Terminator
6234 feet (1900 meters) maximum
PC
Terminator
P
ower
Conditioner
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