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
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