31
Electromagnetic Flowmeter Converter
5.5.2 HART
®
-Protocol
The HART-Protocol provides for simulataneous process value
display and digital communication without requiring any
additional installation. The analog 4-20 mA current output
signal transmits the process values while also providing for
bidirectional communication. The analog output process value
can be utilized by analog indicators, recorders and controllers
while the HART-Protocol provides for simulataneous digital
communication.
The HART-Protocol operates on the Frequency-Shift-Keyed
(FSK) principle based on the Bell 202 Communication
Standard. The digital signal is composed of the two frequencies
1200 Hz and 2200 Hz which represent the bit values1 and 0
respectively.
This design requires the appropriate HART software and a
4-20 mA current output selection.
Ter/- with a load of at least 250
Ω
.
For connection to a PC, a FSK-Modem must be installed for
HART communications. The HART-Modem converts the
analog 4–20 mA current signal into a digital output signal per
Bell 202 with a RS 232C output to the PC.
In addition, the MAG-SM can also be accessed and configured
from a handheld terminal Type 275. A parallel connection is
made to the 4–20 mA current output. Please refer to the
appropriate Hand Held Terminal Instruction Bulletin.
When a mutliplexer is installed and the ABB software package
Smart Vision is utilized all field instrument in the control room
can be centrally configured, monitored and their data values
read for establishing balances using the HART-Protocol. The
Smart Vision Program includes, in addition to its configuration
and display features, a cyclical self monitoring feature for all the
connected field instruments.
Field Multiplexer Model: 55HX1000. See Fig. 16.
R
B
min = 250
Ω
4-20 mA
Bell 202
Modem Box
Fig.14
Communication with the HART-Protocol
Summary of Contents for 50SM1000
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