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Detroit Edison Finds Great Utility In Flo-Dar

Weekly maintenance trips to clean a fouled flow sensor that was submerged in a 10-inch circular sanitary sewer flow was more than a major concern for Detroit Edison's St. Claire engineering staff. They were the group responsible for continuous flow monitoring for a billing application at a local township metering location. The frequent maintenance trips to the site were necessary to clean fouled submerged sensors in an effort to reduce lost flow data.

Detroit Edison, the principal subsidiary of DTE Energy Company, is the nation's seventh largest electric utility serving more than 2 million customers in Southeastern Michigan. The Detroit metro area is home to the nation's auto industry, steel making facilities as well as other major manufacturing facilities. Competition in the energy market has driven Detroit Edison even harder to continue to provide its customers with solutions to their energy needs. Power plants are operating more efficiently enabling electricity rates to drop 8 percent since 1992.

When the site's original flowmeter installed nearly 20 years ago was struck by lighting, they began their search for a replacement meter that could measure flows that ranged from 20,000 to 200,000 gallons per day. Features on their wish list included high accuracy and a sensor that did not have to be installed directly in the flow stream. Such a sensor (if it existed) would eliminate the fouling problems they had encountered with submerged sensors.

A local manufacturer's sales representative contacted Detroit Edison regarding their inquiry into the new non-contact flowmeter being introduced by one his principals. They immediately felt this new technology could solve their flow monitoring problems.

The Flo-Dar Digital Doppler Radar flowmeter manufactured by Marsh-McBirney determines the velocity of the flow in a manner similar to how police radar guns measure the velocity of an automobile. The radar beam is transmitted from the sensor at a defined angle to the flow surface. This transmitted beam interacts with the fluid and reflects a portion of the transmitted signal. The portion of the signal that is reflected is at a slightly different frequency than that which was transmitted. For instance, the frequency is slightly higher if the flow is coming toward the beam and is slightly lower if the flow is going away from the beam. The reflected signals that return to the radar sensor are detected and compared with the transmitted frequency. The frequency shift is a direct measure of the velocity and direction of the flow particles from which the signal was reflected. Flow is then calculated based on the Continuity Equation: Q = V x A, where Q = Flow, V = Average Velocity and A = Area. Operating at a relatively high frequency, the radar flowmeter can measure velocities with only a minimum amount of surface disturbance.

By measuring the fluid from above, Flo-Dar eliminates problems inherent with submerged sensors including fouling, sensor disturbances and other maintenance and accuracy related problems. In most applications the Flo-Dar flowmeter greatly reduces personnel safety concerns by offering sensor retrieval/re-installation without costly (and often dangerous) confined space entry.

When application brochures were presented to Detroit Edison they said that their application was identical to the one depicted in the printed material (see right). The meter was ordered and installed immediately.

The personnel from Detroit Edison now only visit the site twice a year for routine trips significantly reducing their on-going maintenance costs.