Tutorial: Vortex shedding flowmeters

Cost-effective and reliable flowmeter technology retains a high position in process plant toolboxes.

09/18/2008


One technology that scored well in our recent Product Research on flowmeters that we have yet to cover here is vortex shedding. This type of device calculates liquid, gas, or steam flow by observing the vortices formed when a fluid stream passes an obstruction with known characteristics.

When a bar (called a bluff body) is inserted across the interior of a pipe, fluid flowing through the pipe has to pass on one side or the other. As it passes, vortices form on both sides of the body. The frequency of these vortices is determined by the velocity of the fluid stream. Instrumentation devices use a detector to count the frequency, such as strain gages, ultrasonic, capacitance, magnetic, or other types of sensors to generate electrical pulses from the liquid vibrations. The transmitter counts these pulses and converts the reading to a stream velocity from which it calculates fluid volume.

This approach has many advantages:

  • Accuracy and turn-down ratio are sufficient for most general process applications;

  • Relatively inexpensive;

  • Wide range of sizes available;

  • Durable and not prone to drift;

  • Stable, so they need little calibration or maintenance;

  • Good for gas, steam, and liquid;

  • Most can mount in any position so long as the pipe is full;

  • No moving parts;

  • Works with conductive or non-conductive liquids; and

  • Configuration options include spool or wafer designs, and insertion styles for larger sizes.

However, there are some downsides you should keep in mind:

  • Any design that introduces an obstruction causes a pressure drop and creates clogging potential. The extent varies between manufacturers;

  • Solids depositing on the bluff bar can disrupt accurate readings;

  • Two-phase flows and slurries are not well-suited for this kind of flowmeter;

  • Over time, the bluff bar’s shape may change from wear which can cause drift;

  • Liquid viscosity is generally limited to 30 cp;

  • Specific designs can be dedicated either to gas or liquid, but not both; and

  • Ensure sufficient up- and down-stream straight pipe to control turbulence.

Some of the more sophisticated designs add sensors for variables such as fluid temperature and pressure. These readings are often very useful, and can be used to calculate a mass flow reading when known fluid characteristics are added.

These discussions are general, so review specifics with your supplier.

Vortex shedding flowmeters are manufactured by many companies, including:

Aalborg
Cancoppas
GE Sensing
Honeywell PS
Racine Federated
Rosemount (Emerson PM)
Universal Flow Monitors

You can also search online at the Control Engineering Supplier Search .

—Peter Welander, process industries editor, PWelander@cfemedia.com ,
Control Engineering Process Instrumentation & Sensors Monthly
Register here and scroll down to select your choice of free eNewsletters .





No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Motor specification guidelines; Understanding multivariable control; Improving a safety instrumented system; 2017 Engineers' Choice Award Winners
Selecting the best controller from several viewpoints; System integrator advice for the IIoT; TSN and real-time Ethernet; Questions to ask when selecting a VFD; Action items for an aging PLC/DCS
Robot advances in connectivity, collaboration, and programming; Advanced process control; Industrial wireless developments; Multiplatform system integration
Motion control advances and solutions can help with machine control, automated control on assembly lines, integration of robotics and automation, and machine safety.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Big Data and bigger solutions; Tablet technologies; SCADA developments
SCADA at the junction, Managing risk through maintenance, Moving at the speed of data
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
click me