Ultrasonic flow meters are non-intrusive flow sensors, which use acoustic vibration to measure the rate of a flowing liquid. They are important for automated wastewater or dirt liquid applications. But don’t work with drinking or distilled water.

These meters are suitable for low maintenance, chemical compatibility, and low-pressure drop requirements.

How They Work

An ultrasonic flow meter is designed to use sound waves so as to determine the speed of the flowing liquid in pipes. At a no-flow condition, the frequency of ultrasonic waves transmitted to pipes and their reflections are the same. And under flowing conditions, the frequencies of reflected waves are different because of the Doppler system.

When a liquid moves quickly, its frequency increases linearly. A transmitter usually processes signals from a transmitted sound wave and its reflections in order to determine the rate of flowing liquid.

Why Opt for Ultrasonic

One of the reasons to opt for ultrasonic flow meters is the ease of installation. Although the meters still require sections of a straight pipe, the entire process doesn’t need shutting down the system so as to install. This makes the upkeep and maintenance of ultrasonic flow meters more attractive.

Apart from ease of installation, low maintenance is another reason for choosing ultrasonic flow meters. That is because there are no bearings to replace, no electrodes, which may foul over time, and no blades that wear.

Working Principle

Ultrasonic flow meters can be made using downstream/upstream sensors, reflectors, and sensor pipes. Ultrasonic flow meters usually work on a principle that uses ultrasonic waves to resolve the speed of the fluid in a pipe.

As mentioned, there are two cases. These include flow and no flow in pipes. In this first case, the frequencies of reflected ultrasonic waves are different because of the Doppler Effect. In the second one, frequencies of waves are transmitted into pipes.

The shift of frequency can increase linearly every time the liquid flows through a pipe. A transmitter often processes signals from ultrasonic waves, and its timer receives and sends the waves in all directions in a pipe.


There is a meter for every application, ranging from determining how much liquid customers buy to measuring the consistency of a fluid. Different meters may provide accurate and precise data on quantification, mass, flow rate, and volume based on the application’s requirements.

A hybrid ultrasonic flow meter is among the most common type of ultrasonic flow meter. This kind of meter is the most versatile of all. It measures the flow of all kinds of liquids and is called hybrid because it has transit time and Doppler methods.

With transit and Doppler systems available, hybrid ultrasonic flow meters allow users to choose the right method for measuring the flow of liquid. If the flow of liquid contains particulate matter, the transmit system and the Doppler method are used with clean fluid. Apart from hybrid ultrasonic flow meters, other types are:

  • Totalization ultrasonic flow meters
  • Radar flow meters
  • Portable ultrasonic flow meters
  • Single and dual clamp-on ultrasonic flow meters

Final Say!

Every ultrasonic flow meter differs in interface options, user interface options, and output types. Output types for an ultrasonic flow meter can be analog current, pulse, switch, frequency, and analog voltage.

As for interface options, they may include parallel and serial interfaces, while user interface options include computer controls, digital front panels, and analog front panels.