37
57-600 Eclipse
®
Guided Wave Radar Transmitter
2.8
F
OUNDATION
fieldbus
™
Digital Communications
2.8.1 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 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
on a single pair of wires (referred to as a segment).
• 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 digital communications scheme such as Fieldbus considers
the two wires as a network. The network can carry many
process variables as well as other information. The ECLIPSE
Model 705FF transmitter is a F
OUNDATION
fieldbus regis-
tered device that communicates with the H1 Foundation
Fieldbus protocol operating at 31.25 kbits/sec. The H1
physical layer is an approved IEC 61158 standard. The
figure on page 38 shows a typical Fieldbus installation.
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.
2.7.4 HART Revision Table
Model 705
HART Version
HCF Release Date
Compatible with 705 Software
Dev V1 DD V1
July 1998
Version 1.2B and earlier
Dev V1 DD V2
November 1998
Version 1.2C through 1.3D
Dev V3 DD V1
April 1999
Version 1.4A through 1.4C
Dev V4 DD V1
October 1999
Version 1.5 and later
Model 705 2.x
HART Version
HCF Release Date
Compatible with 705 Software
Dev V1 DD V1
June 2000
Version 2.0A through 2.2C
Dev V2 DD V1
September 2001
Version 2.3A through 2.3E
Dev V3 DD V1
September 2003
Version 2.4A through 2.4B
Dev V4 DD V1
April 2004
Version 2.5A and later
Model 705 3.x
HART Version
HCF Release Date
Compatible with 705 Software
Dev V1 DD V2
September 2008
Version 3.0A and later
Dev V2 DD V2
February 2013
Version 3.2A and later
