Of Operation 2

HART MULTIDROP NETWORK FOR TANK LEVEL AND INVENTORY MANAGEMENT

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.


Tank level and inventory management is an ideal application for a HART multidrop network (Figure 19). 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.



Figure 19: 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.

Inventory-Management Applications

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 (see SCADA/RTU Systems on page 25). The HART architecture required just eight cable runs for 84 tanks, with 10–11 devices per run (Figure 20). 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.

Figure 20: Tank Farm Monitoring with Multidrop