Path: EDN Asia >> Design Centre >> Power/Smart Energy >> Tutorial on flow metering (Part 4)
Power/Smart Energy Share print

Tutorial on flow metering (Part 4)

09 Aug 2012  | Mohit Arora, Prashant Bhargava

Share this page with your friends

Part 1 of this series discusses the fundamental concepts and principles incorporated by flow meters along with various flow measurement methods used in mechanical flow meters. Part 2 covers the pulse based counting method and the various sensors that are used in the industry, as well as the way they generate different pulse waveforms to be used in variety of flow meters. Part 3 takes a deep dive on the methods to perform the measurement of these pulses.

Intro to ultrasonic flow meters
These are the type of flow meters that measure the velocity of liquid or gas by using the principle of ultrasound or sounds waves. Fast digital signal processors and sophisticated signal analysis guarantee reliable measuring results even under difficult conditions where ultrasonic flow meters had failed previously.

Advantages over traditional meters
Unlike the traditional meters that have moving parts, ultrasonic meters do not include any moving parts and thus are more reliable, accurate and provide a maintenance free operation. With the homogenous fluids, the principle is independent of pressure, temperature, conductivity and viscosity.

Ultrasonic meters offer completely non-invasive measurement and do not need any pipe construction. Unlike the traditional meters, they don't face the issue of pressure loss.

Since ultrasonic signals can also penetrate solid materials, the transducers can be mounted onto the outside of the pipe and are usable under wide range of nominal diameters (figure 1).

Figure 1: An ultrasonic meter installed directly on the pipe (Reference: http://www.greyline.com/).

An important point to note is that ultrasonic meters are more suitable to measure non-conductive fluids.

Ultrasonic meters: The theory
Swimming against the flow requires more power and more time than swimming with the flow. Ultrasonic flow measurement is based on this elementary transit time difference effect.

Two sensors mounted on the pipe simultaneously to send and receive ultrasonic pulses. At zero flow, both sensors receive the transmitted ultrasonic wave at the same time, i.e., without transit time delay.

When the fluid is in motion, the waves of ultrasonic sound do not reach the two sensors at the same time. This measured "transit time difference" is directly proportional to the flow velocity and therefore to flow volume. By using the absolute transit times both the averaged fluid velocity and the speed of sound can be calculated.

The transducers can be mounted in reflection or in diagonal mode as shown in figure 2.

Figure 2: Ultrasonic transducers mounted in diagonal mode and reflect mode.

Measurement principle: Time of flight and doppler
There are two measurement principles in ultrasonic meters

 • Time of Flight or Transit-time
 • Doppler


1 • 2 Next Page Last Page


Want to more of this to be delivered to you for FREE?

Subscribe to EDN Asia alerts and receive the latest design ideas and product news in your inbox.

Got to make sure you're not a robot. Please enter the code displayed on the right.

Time to activate your subscription - it's easy!

We have sent an activate request to your registerd e-email. Simply click on the link to activate your subscription.

We're doing this to protect your privacy and ensure you successfully receive your e-mail alerts.


Add New Comment
Visitor (To avoid code verification, simply login or register with us. It is fast and free!)
*Verify code:
Tech Impact

Regional Roundup
Control this smart glass with the blink of an eye
K-Glass 2 detects users' eye movements to point the cursor to recognise computer icons or objects in the Internet, and uses winks for commands. The researchers call this interface the "i-Mouse."

GlobalFoundries extends grants to Singapore students
ARM, Tencent Games team up to improve mobile gaming


News | Products | Design Features | Regional Roundup | Tech Impact