New Level Monitoring System Features Foundation Fieldbus

One of the fastest-growing cities in North America, with a population of over 1 million, provides drinking water to a variety of customers, including over 250,000 residential customers and 20,000 industrial, commercial, and institutional customers. To keep up with the growing demand for high quality drinking water, the city invested over $200 million in upgrades to increase the capacity and improve the quality of local drinking water.

One of the upgrades included installation of a new Delta-V Distributed Control System (DCS) with completely new instrumentation using Foundation Fieldbus (FF) communications. FF allows both control engineers and maintenance workers easy access to asset management and diagnostic information over the network via AMS configuration /diagnostic software.

The water treatment plant was using guided wave radar technology to measure the level in one of its tanks. Guided wave radar is contacting level measurement technology: a radar pulse is sent down a cable and is reflected back when the cable comes into contact with the material. The water plant operators chose contacting level measurement technology because the tank contained a ladder with sidebars, and they were worried that non-contacting level measurement would be inaccurate due to the ladder obstruction.

Initially, the system gave accurate level readings but after a few months it started to give false readings. The tank was empty, but the transmitter was reading that the tank was full. When the tank was opened to verify the level reading there was a large amount of lime build-up on the cable, which was causing inaccurate/false level readings.

In addition, the old system would not interface with the new distributed control system. To solve the problem, the water district selected a Siemens Sitrans LR250 level monitoring system with Foundation Fieldbus.

This compact 2-wire, 25 GHz pulse radar transmitter features a small horn antenna and a threaded connection allowing installation directly into the existing opening on the tank. There is no need to remove the lid for programming: the transmitter can be configured using the non-intrusive infrared handheld programmer, or via AMS configuration software over the network. The device provides level readings accurately in a matter of minutes.

A unique feature of the built-in Process Intelligence echo processing software is "Auto-False-Echo-Suppression". This enables the device to ignore structural members inside the tank such as a ladder or sidebars. Since the measurement technology is non-contacting it is unaffected by lime build-up.

The Foundation Fieldbus option fits the communication requirements of the application and supports both Delta-V and AMS. Operators can view echo profiles over the network, making troubleshooting easy. In addition, the level monitor is on the Emerson approved vendor list and has passed their stress test. It underwent rigorous testing and is Fieldbus Foundation approved.

With its narrow beam and small antenna, the level monitor was easily installed on the tank. Process Intelligence echo processing ensured reliable dynamic echo evaluation while ignoring the ladder obstruction. Operators could view echo profiles over the network using AMS software and false readings in the water tank became a thing of the past, allowing operators to have more accurate inventory and control and not disrupting the process.

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