4
48-640 E3 Modulevel
®
Displacer Level Transmitter - FOUNDATION fieldbus
™
1.0 FOUNDATION fieldbus
™
Overview
1.1 Description
F
O
UNDATION
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 dig-
ital 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
E3 Modulevel
®
transmitter is a FOUNDATION fieldbus
™
reg-
istered 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) with-
out a repeater. Up to 4 repeaters
per segment can be used to extend
the distance. The maximum num-
ber of devices allowed on a
Fieldbus segment is 32 although
this depends on the current draw
of the devices on any given seg-
ment. See Figure 1.
Details regarding cable specifica-
tions, grounding, termination, and
other network information can be
found in IEC 61158 or the wiring
installation application guide
AG-140 at www.fieldbus.org.
Control Room
Power Supply
Terminator
6234 feet (1900 meters) maximum
PC
Terminator
Power
Conditioner
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