Coriolis flowmeters are the most accurate flowmeters made. While many magnetic flowmeters have accuracies in the range of 0.5 percent, many Coriolis flowmeters achieve accuracy of 0.1 percent. It is the high accuracy of Coriolis flowmeters that is one of the major reasons for their extremely rapid growth over the past five years. Companies that need flowmeters for custody-transfer or want highly accurate measurements in terms of mass have a good reason to select Coriolis flowmeters.

Suppliers have made a number of improvements in Coriolis technology over the past five years. Coriolis meters are now more adept at measuring gases than previously. The majority of Coriolis suppliers now have meters that can measure gas flow. Straight-tube meters have become more accurate and reliable, thereby addressing some of the drawbacks of bent tube meters. These include pressure drop, the ability to measure high-speed fluids, and the tendency of bent tubes to impede the progress of fluids. And both Micro Motion and Endress+Hauser have broken the price barrier, offering Coriolis meters for considerably less than they were previously.

The large majority of Coriolis flowmeters have in the past been sold for line sizes below two inches. However, in the past several years, a number of companies have brought out Coriolis flowmeters in line sizes above six inches. Despite their higher cost, companies are using these meters due to their high accuracy and reliability. Companies that have entered the large line-size market include Rheonik (now owned by GE Measurement & Control), Endress+Hauser, Micro Motion, and KROHNE.

Until 1994, all Coriolis meters were bent-tube meters. While bent-tube meters still have advantages over many traditional meters, they do introduce pressure drop into the system. KROHNE introduced the first commercially successful straight-tube Coriolis meter in 1994. Since that time, they have become increasingly popular with Coriolis users. Straight-tube meters address the problem of pressure drop because the fluid does not have to travel around a bend.

Jesse Yoder, Ph.D., is president of Flow Research Inc. in Wakefield, Mass., a company he founded in 1998. He has 22 years of experience as an analyst and writer in process control. Yoder specializes in flowmeters and other field devices, including pressure and temperature products. He has written over 110 journal articles on instrumentation topics. Dr. Yoder can be reached at jesse@flowresearch.com.