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WATERMASTER
ELECTROMAGNETIC FLOWMETER | DS/ WM-EN REV. Y
—
…Digital communication
System integration
The GSD file for WaterMasters specifies the device-specific
Ident No. 3431. It conforms to the PROFIBUS standard,
providing a clear and comprehensive description of each
instrument in a precisely defined format.
This enables the system configuration tool to use the
information automatically when configuring a PROFIBUS bus
system.
The ABB GSD file (Ident No. 3431) is divided into 2 sections:
• General specifications
– Identification of the device, together with hardware
and software versions, baud rates supported and the
possible time intervals for monitoring times.
• DP slave-related specifications
– Information about the user parameter block for de-
vice-specific configuration and modules containing de-
tails of the input and output data that can be ex-
changed cyclically with a PROFIBUS master.
The WaterMaster GSD file (ABB_3431.gsd) is available for
download from the ABB website at: www.abb.com/fieldbus
(follow the link for PROFIBUS DP field devices).
MODBUS protocol
MODBUS is an open standard that is owned and administered
by an independent group of device manufacturers called the
Modbus Organization (www.modbus.org).
Using the MODBUS protocol, devices from different
manufacturers exchange information on the same
communications bus without the need for special interface
equipment. WaterMaster FEX100-MB follows the specification
for Modbus Over Serial Line V1.02, using 2-wire TIA/EIA-485
(RS485) physical layer.
Line
terminator
Pull
down
Pull
up
Balanced pair
Slave 1
For example, WaterMaster FEX100–MOD
Slave n
Common
D1
D0
D
D
D
R
R
R
Line
5 V
Up to 31 slaves
Master
Cable Properties
The end-to-end length of the trunk cable must be limited. The
maximum length depends on the Baud rate, the cable (gauge,
capacitance or characteristic impedance), the number of
loads on the daisy chain and the network configuration (2-
wire or 4-wire).
For 9600 Baud rate and AWG26 (or wider) gauge, the
maximum length is 1000 m (3280 ft.). Where 4-wire cabling is
used as a 2-wire cabling system the maximum length must be
divided by 2. The tap cables must be short, never more than
20 m (65.6 ft.). If a multi-port tap is used with n derivations,
each one must have a maximum length of 40 m (131 ft.)
divided by n.
The maximum serial data transmission line length for RS485
systems is 1200 m (3937 ft.). The lengths of cable that can be
used are determined by the cable type, typically:
• Up to 6 m (19.7 ft.) – standard screened or twisted pair
cable.
• Up to 300 m (984 ft.) – twin twisted pair with overall foil
screen and an integral drain wire – for example, Belden
9502 or equivalent.
• Up to 1200 m (3937 ft.) – twin twisted pair with separate
foil screens and integral drain wires – for example, Belden
9729 or equivalent.
Category 5 cables may be used for RS485-MODBUS to a
maximum length of 600 m (1968 ft.). For the balanced pairs
used in an RS485-system, a characteristic impedance with
value higher than 100W is preferred especially for 19200 and
higher Baud rates.
