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An ultrasonic flowmeter can be conceived as many things. Since the popularity of the portable ultrasonic flow meter , a technician may imagine that this is what an ultrasonic flow meter is . However, an ultrasonic flow meter is a device which will either measure the flow velocity , volume or mass flow of a liquid or a gas. There are some companies trying to develop this technology for steam applications but so far the application of these devices is not common and their performance seems to be limited. Ultrasonic flowmeters are manufactured in all sorts of types and applications ranging from transit time or Doppler based flow in blood or bodily fluids, low cost anemometers to incredibly expensive natural gas custody transfer applications. The price for an "ultrasonic flow meter" can range from USD 25 dollars to USD 150,000 or more, depending on the application.

PRINCIPLE OF OPERATION

Most commonly people will distinguish this technology into two types of measurement technique but this is also not entirely true. An ultrasonic flow meter will be categorized into either a Doppler type (which uses the Doppler shift principle) or a transit time device which apparently measures the Delta T or time of flight path. These distinctions have probably been brought about because of the need for simple classifications of ultrasonic flowmeters in the industry. If one takes the time to actually study ultrasonic flow measurement techniques, they will find that some technologies may have been unfairly classified.

Take for instance the Doppler Flow meter where we have Doppler shift being measured by using a continuous wave at a fixed frequency or at varied frequencies as well as the change in Doppler shit being measured using pulses . Some technologies may be using some or all of these principles and even combining them with more popular time of flight techniques.

The transmission of these waves may be through sensors that are in direct contact with the fluid media directly or non contact type and in some cases even both. There can also be misconceptions or oversimplification of transit transit time flowmeters. Some reports classify the early types as "phase shift" meters and then later on we see meters stating they are using "transit time" and then others using cross correlation transit time.

Nowadays we can see manufacturers using combinations of both the transit time and the phase shift information and in combination with other ultrasound technologies so in many cases it impossible to know exactly how a meter is actually functioning and performing calculations without the manufacturer disclosing their actual technique. If one takes time to browse through the many patents that have been published at the US Patent Office it can be a mind boggling task to understand how one patent differs from another unless the reader has already been immersed in several ultrasonic flow measurement techniques prior to the reading.

ULTRASONIC FLOW METER SELECTION

Over the last 40 years, the term" ultrasonic flowmeter " has been seriously damaged , mainly because of inferior designs . However, this is changing in our day and age and we are seeing several companies coming up with much improved measurement techniques, sensors and electronics. Since there are so many companies producing ultrasonic flowmeters using single or multiple variations on a technology, it is almost impossible to make a hard and fast rule on their usage or application since the application could be varied.

The best rule of thumb would be to gather user experience on the application in question and also not confine the experience to one type or one manufacturer of ultrasonic flow meter. Some people have given up on the technology in certain fields of measurement simply because they have suffered some terrible experience at an earlier time in their life