Advanced Electromagnetic Flowmeter Improves Water Nanofiltration Control

Microbubbles in the permeate lines at a water utility in southern Florida caused highly erratic and inaccurate flow measurements. This flow measurement is of prime importance to the water utility because it:

• controls the pressure that forces incoming water through nanofiltration membranes for purification.
• monitors the performance of nanofiltration trains, indicating when cleaning or replacement of the membranes becomes necessary.
• serves as documentation for state permits that limit the amount of water drawn from the utility's wells.
• acts as a check on revenue from downstream customer meters used for custody transfer.

A new FSM4000 electromagnetic flowmeter (magmeter) recently installed at the utility has an unusual design that combines the advantages of AC and DC excitation. The new flowmeter, made by ABB Instrumentation (Warminster, PA), offers a steady, accurate, and responsive flow reading regardless of flow disturbances caused by the microbubbles and line noise. It also eliminates the zero shift usually associated with AC magmeters.