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Two-Wire and Fieldbus-Powered Magnetic Flowmeters

By David W. Spitzer

E-Zine November 2005

There is a quiet evolution going on that may impact your magnetic flowmeters specifications and purchases. If you use or purchase magnetic flowmeters, you need to be aware of this trend.

Two-wire magnetic flowmeters are reported to have been available since 1983, but it was only in the late 1990s that one of the major magnetic flowmeter suppliers introduced magnetic flowmeters using this technology. Soon thereafter, other major suppliers introduced their own two-wire magnetic flowmeters which provided more fanfare about the technology even though some of the flowmeters seemed to be "me too" products.

Although it captured the imagination of some users, the two-wire magnetic flowmeter concept was only sparsely applied in actual installations. It is difficult to tell whether users were not interested in the technology or suppliers were not selling their products. Most likely, the reason why this technology was not widely applied was a combination of the two. Users recognized that the technology had limitations and that performance was generally poorer than that of four-wire magnetic flowmeters. Suppliers found that their four-wire magnetic flowmeters were easier to sell so they did not "push" their two-wire designs.

Nonetheless, the recent introduction of two-wire magnetic flowmeters that rival four-wire performance has caused the movement towards two-wire magnetic flowmeters to gain momentum to the point that neither users nor suppliers will be able to ignore them for much longer. For example, it has been estimated that recently-designed two-wire magnetic flowmeters could be used in upwards of 80 percent of the four-wire magnetic flowmeter applications in the chemical industry.

The first fieldbus-powered magnetic flowmeters will likely be available in late 2006 and 2007. It is expected that their low-flow performance will exceed that of their two-wire counterparts.

Sometimes things heat up --- just when they seem to be quiet.

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ISSN 1538-5280

Spitzer and Boyes, LLC
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