Inventory Management Applications
Accurate measurements for inventory management are essential in
all industries. The HART communication protocol enables companies
to make sure inventory management is as efficient, accurate, and
low cost as possible.
HART Multidrop Network for Tank Level
and Inventory Management
Tank level and inventory management is an ideal application for
a HART multidrop network. The HART network digital update rate of
two PVs per second is sufficient for many tank-level applications.
A multidrop network provides significant installation savings by
reducing the amount of wiring from the field to the control room
as well as the number of I/O channels required. In addition, many
inexpensive process-monitoring applications are commercially available
to further cut costs.
Inventory Management with Multidrop
One company uses a HART multiplexer to digitally scan
field devices for level-measurement and status information. The
information is forwarded to the host application using the Modbus
communication standard. Multivariable instruments further reduce
costs by providing multiple process measurements, such as level
and temperature, which reduces the wiring and number of process
penetrations required.
Multidrop for Tank Farm Monitoring
In one tank farm application, 84 settlement tanks and filter beds
on a very large site (over 300,000 m2) are monitored
using HART multidrop networks and HART RTUs. The HART architecture
required just eight cable runs for 84 tanks, with 10-11 devices
per run. Over 70 individual runs of over 500 m each were eliminated.
Cable savings were estimated at over $40,000 when compared to a
conventional installation. RTU I/O was also reduced, which resulted
in additional hardware and installation savings. The total installed
cost was approximately 50% of a traditional 4-20 mA installation.
Tank Farm Monitoring with Multidrop
Underground Petroleum Storage
with HART Communication for Accuracy
Underground salt caverns are frequently used for crude oil storage.
One customer pumps oil from barges into the storage caverns. An
ultrasonic flowmeter records the total flow. To get the oil out
of the caverns, a brine solution is pumped into the cavern through
a magnetic flowmeter. Brine and crude oil flowing in both directions
are measured and reported to the DCS using the HART communication
protocol for accuracy. The DCS tracks flow rate and total quantity
to maintain a certain pressure inside the caverns.
Use HART multidrop networking to reduce installation and maintenance costs.
Wastewater Treatment Plant Upgrade
A Texas wastewater treatment plant replaced stand-alone flowmeters
and chart recorder outstations that required daily visits for totalization
with a HART system. HART-based magnetic flowmeters were multidropped
into HART RTUs to create a cost-effective SCADA network. The use
of HART technology reduced system and cable costs, enhanced measurement
accuracy, and eliminated time-consuming analog calibration procedures.
A system of 11 HART multidrop networks was used to connect 45 magnetic flowmeters from different plant areas. Each flowmeter communicated flow rate and a totalized value over the HART network. Multidrop networks eliminated the need for additional hardware and PLC programming while providing a more accurate totalized value. Complex and costly system integration issues were also avoided--for example, there was no need for synchronization of totals between the host and field PLCs.
Multidrop networking further reduced the installation cost by reducing
the required number of input cards from the traditional 45 (for
point-to-point installations) to 11. Maintenance was simplified
because of access to instrument diagnostic and status data.