Gas or Liquid: Finding the Right Digital Flow Meter Solution

Flow meters are specially designed instruments used to calculate or measure flow rates of specific gases and liquids moving through a pipeline. Gases and liquids vary greatly, in terms of volume, pressure, temperature, toxicity, etc. There are a number of qualities and characteristics that you need to be concerned about. Consequently, flow measurement methods, constraints, and applications can also be quite diverse from an engineering standpoint.

The different conditions, constraints, challenges, and needs that come with flow measurement require equally diverse solutions. There is no single solution, or one type of flow meter, that can address each and every requirement. For a solution to be effective, it has to fit the appropriate application. And every industry has a different set of requirements for specific applications, which can only be addressed with the right flow measurement tool.

flow-meter

Depending on a particular industry, flow meters are referred to by a variety of names like flow indicator, liquid meter, flow gauge, digital flow meter (for the newer digital designs), and so on. But no matter what you call them, they all serve a single purpose, to measure the flow of liquids and gases. Moreover, the technology behind these instruments also varies according to their unique designs. Some technological designs work better in measuring certain liquids or gases with specific characteristics, while others may not. This is why it is crucial to know the type of liquid or gas you want to measure before you start looking into the different flow meter designs and technologies.

Common Digital Flow Meter Technologies and Their Suited Applications

  1. Ultrasonic Flow Meters

Ideal for:

  • Clean or Dirty Water
  • Corrosive Fluids
  • Abrasives

How the technology works:

As the name suggests, ultrasonic flow meters measure fluid velocity through sound waves. The instrument transmits ultrasonic waves into a pipe and processes signals in order to determine the flow rate of the liquid. Under flowing conditions, the reflected wave frequencies vary due to the Doppler effect. However, if there is no flow occurring inside the pipe, the frequency of the wave reflections remains the same. Fluctuations in the fluid movement inside the pipe, whether it’s flowing faster or slower, can also be detected and measured because of the linear frequency shifts.

  1. Paddle Wheel Flow Meters

Ideal for:

  • Clean Water
  • Corrosive Fluids

How the technology works:

The paddle wheel flow meter utilizes mechanical energy to determine the flow rate of a liquid, just like a riverboat moving through water by way of a huge paddle wheel located at the back. But instead of using the energy generated by the flowing water to move, the paddle wheel itself is stationary with only the paddles on a rotor are actually rotating. When the liquid flows faster or slower, the paddle wheel rotates in proportion to the speed of the flow. A transmitter then detects and calculates the pulse signals generated by each rotation made by the rotor and/or the paddles to determine flow rate.

  1. Vortex Shedding and Fluidic Flow Meters

Ideal for:

  • Cooling Water
  • Corrosive Fluids
  • Clean or Dirty Gas
  • Clean Water
  • Steam

How the technology works:

Flow_Meter

Vortex shedding and fluidic flow meters determine liquid or gas flow rate by way of oscillations as a result of flow. That whistling sound you hear as the wind blows through the branches of a tree, those swirls or vortexes you see as river water flows through rocks and boulders—these are examples of oscillations occurring in nature. The same principle applies to the technology behind vortex shedding and fluidic flow meters. Oscillations are detected by a sensor, and then a transmitter produces a flow measurement signal, generating fairly accurate gas or liquid flow rate.

  1. Differential Pressure Flow Meters

Ideal for:

  • Clean or Dirty Gas
  • Clean Water
  • Cryogenic Fluids
  • Steam
  • Viscous Fluids

How the technology works:

Using Bernoulli’s equation, differential pressure flow meters can measure the flow rate of liquids and gasses in a pipe. A method of constriction is introduced in the pipe that essentially creates a pressure drop across the flow meter. As liquid or gas flow increases, more pressure drop is generated in the flow meter. Downstream and upstream pressures are routed through impulse piping and into a transmitter, which calculates differential pressure to establish the flow rate of the liquid or gas. Differential pressure technology holds around 21% of the world market for flow meters.

  1. Positive Displacement Flow Meters

Ideal for:

  • Clean Oil
  • Clean Water
  • Viscous Fluids

How the technology works:

Most flow meter technology can only measure the flow rate of fluids passing through a pipe. This technology, however, is the only flow measurement tool that can also directly measure the volume of the liquid as it passes through the meter. Positive displacement flow meters work by repeatedly entrapping a certain amount of fluid to measure flow, as well as volume. The principle can be compared to a person repeatedly filling up a bucket with water and dumping it into a canal. The number of times that he fills and empties the bucket measures the volume and the flow through the meter.

  1. Magnetic Flow Meters

Ideal for:

  • Corrosive Fluids
  • Abrasives
  • Clean or Dirty Water
  • Fibrous Fluids
  • Viscous Fluids

How the technology works:

Magnetic flow meters, or electromagnetic flow meters, measure the flow rate of liquids by way of Michael Faraday’s Law of Electromagnetic Induction. In an electromagnetic flow meter, a magnetic field is created and channeled into the fluid moving through the pipe. Electrodes positioned on the flow tube walls act as sensors that detect voltage signals generated by the conductive fluids passing through the magnetic field. As stated in Faraday’s Law, the voltage created is directly proportional to the velocity of the moving liquid. An electronic transmitter processes the voltage signal to calculate flow rate.