Picking the perfect flowmeter for your process measurement and control needs can be difficult. There are so many different flow measurement technologies available, and so many different models for each type, that your choices can seem virtually endless.
However, some flowmeter technologies do set themselves apart from the rest in terms of accuracy and reliability. Two such technologies are Coriolis mass flowmeters and ultrasonic flowmeters.
Of these two, which is better for your particular application? The answer depends on the specific nature of your application, as each of these flow measurement technologies have their own strengths and weaknesses.
Let’s take a look at these strengths and weaknesses for comparison:
About Ultrasonic Flowmeters
Ultrasonic flowmeters operate in one of two ways:
- Transit Time Flowmeters. These units use two ultrasonic transducers that send ultrasonic waves back and forth. The difference between the upstream and downstream transit times is used to measure the flow rate.
- Doppler Flowmeters. These units use a single transducer to transmit an ultrasound wave into a fluid, and then catches the reflected wave to measure the flow rate. The faster the flow, the more distorted the reflected wave will be.
Ultrasonic flowmeters can have numerous strengths. High accuracy (typically about ±0.5% to 1% of flow) is a hallmark of this technology. The repeatability of measurements with these devices is also strong (± 0.05% of flow).
Another strength of this technology is that there are clamp-on versions which can be attached to the outside of a pipe. This allows for accurate flow measurement without needing to cut into your pipes, practically eliminating the risk of creating a leak point when installing these flowmeters.
Additionally, if you’re able to invest in them, ultrasonic flowmeters with multiple paths are available. The more paths the ultrasonic flowmeter uses, the less affected it will be by swirl and asymmetry in fluid flows, allowing you to place these meters close to a bend in your pipe.
Some drawbacks include a high initial cost (especially for 4-path or higher meters), interference from pipe walls when using clamp-on models, and possible interference caused by vibrations and noise from external sources.
About Coriolis Mass Flowmeters
Coriolis mass flowmeters are among the most accurate meters on the market today for measuring the flow of liquids. By passing fluids through a set of oscillating or vibrating tubes, the tubes will twist. Coriolis flowmeters measure the amplitude of this twist to calculate flow.
Part of the reason why these flowmeters are so accurate is that, unlike volumetric flowmeters, mass flowmeters take their flow measurements directly. These meters are also reknown for their reliability and their measurement repeatability (often as strong as ±0.05%), especially in measuring fluids in smaller-size pipelines (2” or smaller).
Key weaknesses of this technology include a loss of accuracy when measuring low-density gases, pressure drops in bent-tube meter designs, and high initial setup costs.
Which is Best?
Both of these technologies can be excellent process measurement tools, depending on your needs. Each of these technologies have high initial costs, but low cost of ownership over time compared to other common flowmeter types. Also, both of these flowmeters are highly accurate, with a high repeatability.
So, which is better?
If you need to measure low-density gases, or are worried about creating leak points, ultrasonic flowmeters are probably the better option for you.
If you need top-notch accuracy for liquids in custody transfer applications, or want to directly measure mass flow rather than using claculated inferred mass, then you may prefer to use a coriolis mass flowmeter.