A comparison of common flow sensor typesTim Cannon | June 08, 2022
There are many different types of flow meters used in industry today and more technologies are being developed right now. After researching all of the different types of flow meters, it might be easy to get confused among the myriad options. How do you know what type of flow meter is right for your application?
This handy guide is quick overview of the most common types of flow meters and applications.
Coriolis flow meters
Coriolis flow meters are a unique type of flow meter that is used for measuring both liquids and gases. These flow meters measure the inertia of the fluid and use that to calculate the mass flow of the fluid. This is accomplished by vibrating a small tube through which the fluid flows. This creates a force acting against the tube, which can be measured. The actual mass flow rate is determined by the angular momentum of that tube.
These flow meters have several big advantages. They are extremely accurate and are also extremely repeatable. These devices can measure flow both forwards and backwards and are compatible with a wide variety of gases and liquids.
Differential pressure flow meters
Differential pressure flow meters are one of the most tried and true methods for measuring flow. These flow meters utilize Bernoulli’s equation in order to calculate a flow based off of a pressure differential. These meters will create a constriction in the flow path of the fluid and as the liquid flows through this constriction, it will create a pressure drop that increases with higher flow. By measuring this pressure differential and utilizing Bernoulli’s equation, these meters can calculate a flow.
Suitable for application with liquids, gases and even steam, these systems are extremely common and can be very accurate. They also support a very wide temperature and pressure range since the transmitter itself is usually relatively far from the fluid flow path. They are also great for measuring extremely low flow rates and are the most common type of flow meter in industry and for good reason.
Ultrasonic flow meters
Ultrasonic flow meters are another type of flow meter used primarily for measuring the flow of liquids. These function by emitting ultrasonic sound waves through the fluid and then receiving the sound wave on the other side of the tubing. The time that it takes the sound wave to pass through the fluid is used to calculate the flow of the fluid as the velocity of the fluid is proportional to the transmit time.
One of the greatest advantages of using ultrasonic flow meters is that they can be extremely simple to install. Many of come in a “clamp on” style that emits the ultrasonic sound waves through the tubing or piping. As such, to install these, users only need to clamp it onto the outside of a pipe or tubing. Thus, installation and removal are extremely quick and do not require shutting down the system. In addition, as these flow meters utilize sound, there aren’t any components like bearings or seals that will wear out over time.
Electromagnetic flow meters
Electromagnetic flow meters, often called magnetic or mag flow meters, are another type commonly used to measure water-based fluids. These flow meters do not have any moving parts and as a result are great for applications that require minimal pressure drops. Fluid channels through a magnetic field generated by the flow meter, and as it passes through generates a voltage that is larger with higher flow. Measuring this voltage allows for the flow to be determined.
As these flow meters have no moving parts, they are great for applications where minimal maintenance is a necessity. In addition, the flow of the fluid is barely affected so operators don’t have to accommodate for larger pressure drops in a system. While these flow meters are great for fluids that are extremely conductive (such as water), they don’t work very well for fluids with low conductivity. If a water-based fluid is being measured, electromagnetic flow meters are an excellent choice.
Vortex flow meters are one of the newer flow measurement technologies available. These utilize what is known as the Von Karman effect and place what is called a shredder bar directly into the path of the fluid. As such, the fluid will begin to develop vortices that are picked up by a sensor oscillating proportionally to the fluid velocity. This oscillation frequency is converted to a voltage and can easily be used to measure the flow of the fluid.
Vortex flow meters work great for most fluids and can accommodate gases, steam and any liquid with a lower viscosity. On top of that, many of these styles of meters are capable of measuring a wide variety of different parameters apart from just flow so that operators can now obtain information such as heat transfer, mass flow and volumetric flow. One large drawback to vortex meters is that they only work with turbulent flow. As a result, in very low flow applications where the flow might begin to transition to laminar, the meter becomes incapable of measuring the flow.
So, what flow meter is best?
As we’ve discussed, there are many different types of flow meters out there, each with its own pros and cons. There is not a one size fits all best flow meter. Every application is different, so users will need to weigh out the pros and cons of each of the different styles to find the perfect match for each system. Common factors that affect this decision are fluid media, connection requirements, maintenance requirements, temperature requirements, accuracy requirements and pressure drop requirements.
About the author
Tim has a bachelor's degree in mechanical engineering from BYU-Idaho. He currently works as a control systems engineer for Ram Aviation, Space and Defense, where he designs pneumatic and hydraulic valves, and as a LabVIEW consultant for EZtech-stop. He has worked for Hyundai as a Thermal Systems Engineer and the Idaho National Laboratory as a Nuclear Systems Engineer in the past.