Learn the features of these two common devices.

Flow meters are important devices for many industries that require measurement of the rate or quantity of a gas or liquid moving through a pipe.

There are different types of flow meters, and there is not a “one-size-fits-all” solution. When it comes to choosing which device is best for a particular application, it is recommended that decisions be based on the merits of the technology rather than trying to make the technology fit the application.

Remember that lower-priced alternatives may not have the ability to meet a user’s requirements.

It is important to know the critical specifications of the different technologies. When considering a flow meter, the following discussion on the key features of two of the main types—ultrasonic flow meters and electromagnetic ones—will be helpful.

These two technologies account for more than 85 percent of the market, with the growth of ultrasonic flow meters tipped to escalate in the future.

Electromagnetic flow meterImage 1. Electromagnetic flow meter (Images courtesy of Nexxis)

Key Features of Electromagnetic Flow Meters

An electromagnetic flow meter (sometimes called a mag meter) uses Faraday’s Law of Electromagnetism to measure flow rates.

It creates a magnetic field by running electric current through a coil surrounding the flow tube.

Electromagnetic flow meters include the following features:

  • accurate to +/- 0.25 percent of reading
  • designed for systems that move conductive liquids such as water, acids, caustic liquids and slurries
  • performance is not inhibited by viscosity, temperature and pressure
  • responds well to rapid changes in flow
  • suitable for liquids with heavy particulates
 Ultrasonic flow meter Image 2. Ultrasonic flow meter

Key Features of Ultrasonic Flow Meters

Ultrasonic flow meters use ultrasound waves to calculate flow through a pipe and are used to measure a variety of fluids including water, natural gas, mineral oil, chemicals and dirty liquids. It is an accurate, nonintrusive process and the clamp-on devices can measure flow from the outside of plastic, metal or concrete-lined pipes, regardless of size.

  • no moving parts meaning minimal maintenance
  • easy to install and operate
  • cost-effective
  • clamp-on transducers are noninvasive, so they do not interfere with the pressure or contaminate the process
  • not affected by extreme temperature variations nor changes in viscosity, density or pressure
  • does not obstruct flow so they can be applied to sanitary, corrosive and abrasive liquids

An ultrasonic flow meter is an important nondestructive testing device when it comes to ensuring consistent quality, safety and environmental protection. They provide accurate measurement of liquid and gas flow across a wide variety of applications including process control, water resource management and effluent control as well as in the power, chemical, food and beverage, pharmaceutical, metals and mining, pulp and paper, and oil and gas industries.