Flow Measurement: Market Forces Drive Technology Improvements

Flow measurement is one of the most important functions in modern industrial plants. Whether the application involves oil from a well, hydrocarbon in a refinery, or steam in a chemical plant, accurate flow measurement is essential to efficient and productive manufacturing operations.

Types of Flowmeters

Most flowmeters can be classified among the types given below:
Handheld Ultrasonic Flowmeter
Wall-Mount, Clamp-on Transit-Time
Economical Flowmeter
Thermal Energy Meter, BTU
The lists flowmeter types, along with a brief description of the technology,visit our site.

Flowmeter Advantages and Disadvantages

While reasons for selecting one flowmeter over another vary, users typically make their decisions based on the perceived advantages and disadvantages of the flowmeters they are considering. A complete list of advantages and disadvantages would take into account at least these criteria: accuracy, reliability, purchase price, installed cost, cost of ownership, ease of use, capability of measuring liquid, steam, and gas, rangeability, turndown, degree of smartness, repeatability, pressure drop, intrusiveness, Reynolds Number constraints, sizes available, maintenance, sensitivity to vibration, and upstream and downstream piping requirements

Volumetric Flow vs. Mass Flow

Flow in a pipe is the actual volume of fluid that passes a given point in a specified unit of time. Volumetric flow (Q) can be calculated by multiplying the cross-sectional area of the pipe times average fluid velocity. Typical units of volumetric flow include gallons (or liters) per minute and cubic feet (or meters) per minute.
The flow of gases is normally measured in terms of mass per unit time. Mass flow (W) of a gas can be calculated by multiplying its density (r) times the volumetric flow. Typical units of mass flow include pounds (or kilograms) per minute and standard cubic feet (or meters) per minute.

New Technologies Displace Traditional Approaches

One of the most significant trends in todays flowmeter market is that new technologies, such as Coriolis mass, ultrasonic, and vortex, are displacing traditional DP flowmeters that use orifice plates and other primary elements. These newer technologies are also displacing turbine and positive displacement flowmeters.
The increasing need for highly-accurate measurements is the principal driving force behind the increased use of Coriolis mass flowmeters. Ultrasonic flowmeters are being used more because they are nonintrusive, have wide rangeability, and are substantially more accurate than they were ten years ago.

Multivariable Flowmeters for Inferred Mass Flow

Most volumetric flowmeters, such as DP-based flowmeters, sense a single process variable and calculate volumetric flow based on this parameter. The past few years, however, have seen the introduction of multivariable flowmeters that measure more than one process variable, and produce more than one output.

Changes in the Primary Element Market

In addition to introducing multivariable flowmeters, some pressure transmitter suppliers are taking a new look at the role of primary elements in the measurement of flow. In many cases, users purchase their pressure transmitters from one supplier and their primary elements from another.

On-going Flow Measurement Development

Primary flow elements are important because they place a limitation on the accuracy of any flowmeter using them. Today, users are attaching pressure transmitters with 0.5% accuracy or better to orifice plates that have 3% accuracy or greater. Even if an orifice plate has an initial accuracy of better than 3%, this accuracy typically degrades with use. Yet the accuracy of any flowmeter system is no better than the accuracy of its weakest element. As a result, highly accurate transmitters are sending digital signals to the controller that can be carried out to any desired degree of precision, but that carry the baggage of inaccurate sensing elements.