What is Flow Meter? How it Works and Its Types

Also known as a flow sensor, a flow meter is a device designed for measuring nonlinear or linear flow rate. It measures the volumetric or mass flow rate of gases or liquids. Before choosing a flow meter to use in an application, a few factors need to be considered. These factors include whether or not the personnel is familiar with the plant. Does it know how to maintain and calibrate the device? What about the meantime failure history? Are spare parts easy to get based on the plant site? After going through all these, the next step is to compute the setup cost.

In plants that make or use fluids, getting the flow rate is crucial. This data is vital because it determines whether the company makes profits or loses. In other words, a flow meter is a tool used to measure either mass or volumetric flow rate or the amount of fluid flowing inside a pipe.

Flow Measurement Overview 

Flowmeters are tools used to monitor the amount of vapor, liquid, or gas passing through them. Some flowmeters are meant to measure the fluid amount flowing inside them after a period of time (100 liters per minute, for instance). Other flowmeters are meant to count the total amount in liters of fluid that has gone through them (such as 100 liters).

Most flowmeters have three parts: the primary device, a transducer, and a transmitter. The work of the transducer is to sense the fluid passing the primary device. Raw signal from the transducer is then turned into usable data by the transmitter. A flowmeter may consist of one or many physical devices since these components are most of the time combined.

What is the Purpose of a Flow Meter?

Flowmeters are used to measure the mass flow rate or the volumetric flow rate of a fluid in many types of applications. The type of airflow meter is based on its application. Volumetric flow rate and mass flow rate are units used to measure gases and liquids. Both volumetric mass rates are related to the density of the fluid. Q denotes the volumetric flow rate, and ṁ denotes the mass flow rate in the equation ṁ=Q x ρ.

The Main Step to Choose the Right Flow Meter

Knowing whether the flow rate data will be continuous or totalized is the first step in picking the right flow meter or sensor. One should also know whether the info given will be relayed remotely or locally. Should it be done locally, will it be transmitted digitally or analog, or shared. If it is going to be shared, what will be the min and max data update frequency required. When all these are addressed, what follows is an evaluation of the fluid flow properties. The piping system that the fluid will flow through also needs to be stated.

This task is done in an organized manner by creating forms that these data types are going to be entered in each application:

Download the Flowmeter Evaluation Form.

mass flow meter- Flow meter

Image Source: Omega

Fluid and Flow Characteristics 

The fluids are described by their pressure, conductivity, temperature, density (or specific gravity), allowable pressure drop, viscosity (Newtonian or not?), and vapor pressure at maximum operating temperature. All these forms define a certain fluid that is going to be measured by the airflow meter.

Another aspect that should be stated is how these fluids interact or vary from one another. Moreover, all toxicity and safety information needs to be known. Details of data on the fluid’s presence of a bubble, the tendency to coat, light transmission qualities need to be known. The presence of solids in fluid should be stated, including the size of particles, abrasive or soft, and fibers.

Also, you can read High-Quality Liquid Flow Control Valve for Systematic Flow of Liquids

Pressure & Temperature Ranges

Another vital piece of info that should be laid bare when choosing a flowmeter is about temperature value. What are the expected min and max pressure? Data about the normal operating values should also be known when choosing a flow meter. It is also good to know if sudden temp changes are expected and whether extra safety measures are required when cleaning or carrying out repairs. The system efficiency also depends on knowing whether slug flow will be present (air-solids-liquid). Users should also know whether the flow will always fill the pipe or whether the flow can reverse. Will the flow always feel the pipe or not? Knowing if pulsating and aeration will be there is also vital.

Flow Meters – How Do They Work?

A flow meter is meant to measure the amount of gas, steam, or liquid passing around or through it. Although there are many kinds of flow meter sensors that work in different ways, they all have one set goal, and that is to give the most accurate flow rate report based on the application. The data gotten could either be for general research, process control, or processing. Flow meters are either used to measure volume or mass.

In a volumetric flow meter, the flow (Q) is equal to the cross-sectional area of the pipe (A),

and the flowing fluid’s velocity (v): Q = A * v. In mass flow, the flow rate in a flow meter is given as ṁ = Q ∗ρ ( ρ here, is the fluid density and Q is the volumetric flow rate).

Many times, sectors consider mass flow rate, more so in combustion, selling or buying gases, or chemical reactions.

Choose the right Flowmeter

6000 Series

In Proteus 6000 Series Flow Meters, a simple turbine principle is used to create a pulse output that’s directly proportional to the flow rate. When fluid is going through the flow sensor, a Hall Effect transistor is turned on and off by magnets in the six-spoke rotor. Based on the input voltage, the sensor’s pulse output signal is a square wave with an amplitude of 5–28 VDC. At each meter’s max flow rate, the output frequency ranges to 240 Hz. NPN and PNP outputs are given.

6000 Series- flow meter

6000 Series Flow Meter

Easy interfacing due to pulse output with your PLC

  • Flow rates from 0.2 to 227 LPM / 0.06 to 60.0 GPM
  • Has an option for RTD temperature integration
  • The pulse output from 5–24 VDC
  • FluidVision USB option
  • Can be customized for OEMs
  • Optional digital display
  • 5-year warranty

PV6000 Series Vortex Flow Meters

PV6000 Series flow meters provide cost-effective, accurate, and concise reading of heat-transfer fluids and other liquids using the vortex principle. The total frequency of vortices shed by a bluff body is detected by an in-line sensor in the flow stream. A pulse output signal is then generated, which is directly proportional to the liquid’s flow rate.

You can check out Vortex Flow Meters

PV6000 Series Vortex Flow Meters - flow meter

Vortex Flow Meters

  • Flow ranges from 0.9 to 85 LPM / 0.2 to 22 GPM
  • Better than 3% of flow range accuracy
  • Measures from -40 to 100°C / -40 to 212°F liquid temperatures
  • No moving parts – performance is not affected by fluid!
  • Optional integrated temperature sensor
  • Rugged glass-fiber-reinforced PPA construction
  • Interfacing with your PLC is made by 0–10 VDC or 4–20 mA analog output or pulse output
  • IP65 enclosure
  • Can customize for OEMs

FluidVision™ USB

FluidVision™ USB - flow meter

FluidVision™ USB from Proteus provides an easy and affordable method to connect flow meters directly to a PC. By doing this, it results in the reliable and accurate flow rate of liquids in closed-loop cooling systems. Through the standard USB connection, the output signals from temperature sensors and compact flow are monitored, analyzed, and transmitted for on-screen display in real-time. Accuracy is ensured by sensor-specific calibration factors stored in the device memory. Alarm accuracy for both flow and temperature have advanced monitoring capabilities.

Monitoring and collection of status data and flow rate from FluidVision USB devices is done using a software application. The measurement can also easily be incorporated into existing monitoring and data-acquisition systems.

FluidVision™ USB Flow and Temperature Meters

  • A standard USB port connects flow sensor directly to a computer
  • No auxiliary power needed since electronics and paired flow sensors are powered by a USB port
  • Both flow rate and temperature have multiple programmable alarm levels
  • System monitoring and data-logging are done using specialized software
  • Compatible with V7000 Series and PV6000 Series vortex flow meters with pulse output
  • Compatible with Windows XP, Windows Vista, and Windows 7
  • 5-year warranty

How much maintenance does a flowmeter require?

A flow meter’s maintenance and lifespan is influenced by various factors. One obvious factor is using the right flow meter with the right application. Failure to match a proper flow meter to the right application will lead to breakages and device damages at an early stage. Flow meters that consist of moving parts usually need more attention in terms of maintenance than flow meters with no moving parts. However, all flow meters require maintenance one way or another.

For over 30 years and now, Proteus is offering the best flow meter products to valuable clients. Some industries that use our devices like flow meters, flow-switches, and sensors are medical, thermal industries, and technicians. Proteus products like sensors are used to guard thousands of robotic welders, induction furnaces, and devices that include plasma cutting and high-power laser systems. You can order the products according to your preference. Customization is available on many of the products.

Proteus has an ISO 9001 certified quality system.


How is flow measured? Flow is generally measured either by weight or volume of the fluid.

1. How is the flow rate calculated?

For example, if you fill up a 50 Liter bucket in 10 minutes, you can calculate the flow rate as 50/10 = 5 Liters per 1 minute.

2. Where are flow meters used?

Flow meters are usually used in domestic and various industrial sectors to measure the volume or mass of a liquid or gas, depending on the application.

3. Which flow meter is the most accurate?

Although Coriolis mass flow meters are costly, they are the most accurate types of flow meters.

4. How do you calibrate a flow meter?

Calibration in flowmeters can be done in various ways that mainly entail contrasting and adjusting the flow meter to conform to a standard under test.

5. What is the unit for measuring flow?

Liquid flow measurement is usually measured in cubic meters/second, gallons/minute, and units of cubic feet/second.

There you go, an overview of a flow meter. It is a unique device for measuring gas flow rate, steam, or liquid that goes inside a pipe. Various kinds of applications such as natural gas, compressed air, mixing and blending of gas, water, burner control, boiler efficiency, & steam flow.

Here is a question for you: Do you know the pros and cons of flow meters?

Here are a few more topics that you shouldn’t miss:
How to Find the Right Liquid Flowmeter Manufacturer
What Is Plasma Cutting And Best Sensors To Protect Plasma Cutting Systems?
Different Types of Standard Liquid Flowmeter

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