How Many Types of Inline Flow Meters?

First, you need to understand what factors to consider when selecting a flow meter. Before choosing the right type, it’s essential to clearly define your application purpose. Are you measuring gas, liquid, or steam? Let’s start by understanding what a flow meter is, how it works, its main applications, and the key criteria for selecting the right one for your process.

What is a Flow Meter?

A flow meter is an instrument used to measure the mass or volumetric flow rate of gases or liquids. When discussing flow meters, you may come across various related terms such as flow sensor, mass flow meter, mass flow controller, or flow transmitter.

The primary purpose of a flow meter is to measure the flow of gas or liquid between two points in a process. Sometimes, it’s also necessary to control or regulate the flow. This can be achieved by combining a flow meter with a valve to create a flow controller, which not only measures flow but also adjusts it as needed. The flow meter’s output provides valuable data that helps you better understand your process, make informed decisions about product quality, optimize production speed, and reduce overall costs.

How Does a Flow Meter Work?

There are two main types of flow measurement: mass flow measurement and volumetric flow measurement.

Volumetric flow measurement is influenced by temperature and pressure—especially for gases—and the readings are displayed in volumetric units such as mL/min or m³/h.

Mass flow measurement, on the other hand, provides results in mass units such as kg/h or g/min.

Because gases are compressible, it’s often more convenient to express mass flow in standardized volumetric units such as sccm (standard cubic centimeters per minute) or Nm³/h (normal cubic meters per hour). Therefore, depending on your specific application requirements, you can choose either a mass flow meter or a volumetric flow meter.

Common Types of Flow Meters

There are several types of on-line flowmeters on the market. The main on-line flowmeters are turbine flowmeters, electromagnetic flowmeters, water meters. Today, ARTang will tell you how to choose the most suitable online flowmeter according to your own needs.

Electromagnetic Flow Meter

An electromagnetic flow meter is a volumetric measurement instrument for conductive liquids, based on Faraday’s Law of Electromagnetic Induction. It features high measurement accuracy, excellent stability, and fast response time.

One of its key advantages is that its measurement accuracy is not affected by changes in fluid temperature, pressure, viscosity, or density. It is suitable for measuring the flow of all types of conductive liquids—especially those containing suspended solids or fibers—making it ideal for industrial applications such as wastewater treatment, chemical processing, and pulp and paper production.

Ultrasonic Flow Meter

An ultrasonic flow meter measures the volumetric flow rate of a fluid by detecting how the fluid’s movement affects the transmission of ultrasonic waves. Unlike electromagnetic types, it can measure non-conductive liquids.

It offers non-intrusive measurement, easy installation, and no flow obstruction, making it suitable for pipelines of various diameters—particularly for large pipes or fluids that are difficult to access.

However, ultrasonic flow meters are more sensitive to impurities, air bubbles, and uneven flow velocity profiles, which may slightly affect measurement accuracy under certain conditions.

Vortex Flow Meter

A vortex flow meter operates by placing a bluff body (vortex generator) in the flow path. As the fluid passes the bluff body, it generates vortices whose frequency is directly proportional to the flow velocity, allowing the meter to calculate the volumetric flow rate.

Vortex flow meters are suitable for measuring liquids, gases, and steam. Since they have no moving parts, they offer excellent durability and require minimal maintenance. They perform exceptionally well under high-pressure conditions and are particularly effective in steam measurement, making them an ideal choice for industrial process monitoring.

Coriolis Mass Flow Meter

A Coriolis mass flow meter measures mass flow by detecting the Coriolis force generated when a fluid flows through a vibrating tube. As the fluid passes through the oscillating measuring tube, it causes a slight twist or deformation. By detecting this degree of deflection, the instrument determines the mass flow rate of the fluid.

Coriolis flow meters offer high accuracy and are unaffected by temperature, pressure, or viscosity changes, making them ideal for applications that demand precise mass flow measurement. However, they are structurally complex and more expensive than other types of flow meters.

Turbine Flow Meter

A turbine flow meter measures flow by detecting the rotational speed of a turbine driven by the fluid passing through it. The turbine’s rotational speed is proportional to the fluid’s velocity, from which the flow rate is calculated.

This type of meter provides high accuracy, excellent repeatability, and fast response time, making it well-suited for measuring clean liquids and gases. However, its performance can be affected by changes in fluid temperature, pressure, and viscosity, and over time, mechanical wear on the turbine may reduce measurement accuracy.

Which Flow Meter Is Best for Measuring Dirty Liquids?

Electromagnetic flow meters are the top choice for dirty fluids or slurries because they have no obstructions or moving parts. These meters handle conductive dirty liquids, slurries, and corrosive substances extremely well, as there are no components that can clog or wear out. Ultrasonic flow meters are also suitable for fluids containing particles — in fact, Doppler-type models actually require suspended solids in the flow to operate correctly.

Which Types Are Suitable for Gases, and Which for Liquids?

Some flow meters are not equally effective for both gases and liquids. Thermal mass flow meters excel in gas applications, especially for air, natural gas, and biogas. They perform exceptionally well even at very low flow rates (as low as 25 ft/min), where other technologies often fail.

On the other hand, electromagnetic flow meters are designed only for conductive liquids (conductivity > 5 μS/cm) and cannot measure gases or oils. Coriolis flow meters are highly versatile, capable of measuring both liquids and gases with very high accuracy (±0.1%). Vortex flow meters are suitable for all types of flow media — gases, liquids, and even saturated steam.

There are many types of flow meters with various classification methods. Different flow meters differ in their measurement principles, applications, media, and installation methods, making them suitable for different measurement scenarios and requirements. When selecting a flow meter, it’s important to consider factors such as measurement accuracy, response time, measuring range, and installation conditions based on actual needs. Attention should also be given to calibration and maintenance to ensure the flow meter’s accuracy and reliability.