• Flow meters measure the flow of gas or liquid streams and are often combined with a valve to control and change the flow rate
• When selecting flow meters, consider the phase and content of the process stream, flow rate range, process pressures and temperatures, and installation requirements of the flow meter
• Some applications can use low cost and quality flow meters while other applications may require high performance, accuracy, and repeatability, or flexible use

Do you need a flow meter for your application? You’ll need to know what aspects you should take into consideration when selecting the best flow meter for your application. We will guide you along the way to help you make an informed selection.

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Before you can start conducting experiments or developing skids for your customers, it is essential that your research setup or your system is working properly. A key component herein is often a flow meter. This can be a gas, liquid, or vapor instrument. Of course, there is a big difference between laboratory research and industrial applications but most of the considerations are required for all application fields.

But first, let’s explain a bit more about what flow meters are, how they work, what they are used for, and the criteria to select the best flow meter for the application.

Learn More About Flow Meters in our 6 Modules:

1. What is a flow meter?
2. How does a flow meter work?
3. How to select the best flow meter
   • Phase of the fluid: gas, liquid, vapor 
   • For which fluid do you use the flow meter?
   • What is the flow rate?
   • What is the inlet and outlet pressure?
   • What is the ambient temperature and the temperature of the fluid?
   • What is the location of the flow meter?
4. What do you want to achieve with your flow meter?
   • Performance versus price  
   • Flow meter accuracy versus repeatability 
   • Flexible use
5. Which process conditions can be relevant?
6. Examples of applications that use flow meters

The basic purpose of a flow meter is measuring the flow of gas or liquid between two points in a process. Sometimes controlling or regulating the flow is necessary. This is done by combining a flow meter with a valve, creating a flow controller. In this case, besides measuring a flow, you can also control it to change the flow rate. The output can help you understand your process better to make decisions regarding product quality, speed of process, and cost reduction.

2. How Does a Flow Meter Work?

There are two basic types of fluid measurement – mass and volume flow measurement. The volumetric flow measurement is temperature and pressure dependent and will be shown in units of volume such as ml/min or m3/h. When measuring mass flow, you see units of mass such as kg/h or g/min.

However, mass flow is frequently expressed as standardized volumes. The European definition uses an underlying “s” or “n” to indicate standard or normal reference conditions, respectively (e.g. mls/min or m3n/h). Whereas the American definition uses an “s” as the beginning of the unit to refer to standard reference conditions (e.g. sccm or scfh). Therefore, you can either choose for a mass flow meter or a volumetric flow meter for your application.

Besides these two types of measurement, there are different measuring principles that all have their specific advantages and disadvantages:  

Mass Flow Measuring Principles

• Thermal measuring principle; within this category we distinguish three sensor principles:
  • By-pass principle for gases
  • Inline CTA for gases
  • Inline CTA for liquids
• Coriolis measuring principle

Volume Flow Measuring Principles

• Ultrasonic flow measurement
• Vortex
• Magnetic inductive
• Differential Pressure
• Positive displacement

Gas & Liquid Flow Meters

Some flow meters are developed for gas flow control, some especially for liquid flow control. There are also flow meters available on the market that are independent of the fluid properties and therefore can handle both gas and liquids.

3. How to Select the Best Flow Meter for Your Application

In this section, we will discuss some of the essential elements that go into the decision making process of selecting a flow meter. Thereby, we consider the differences between various measurement principles.

Phase of the Fluid: Gas, Liquid, Vapor

Some flow meters can be easily eliminated because they simply will not work with the application. For instance, electromagnetic flow meters will not work with hydrocarbons and require a conductive liquid to function. Many flow meters cannot measure vapors or slurries. Listed below are some of the main flow meter categories paired with the fluid type the meters can handle:

• Gas – Coriolis Mass, Thermal Mass, Ultrasonic, Variable Area, Variable Differential Pressure, Positive Displacement, Turbine 
• Liquid – Coriolis Mass, Thermal Mass, Ultrasonic, Variable Differential Pressure, Positive Displacement, Turbine, Electromagnetic 
• Slurry – Coriolis Mass, some subsets of Variable Differential Pressure, Electromagnetic, Ultrasonic
• Vapor – Vortex, Ultrasonic, Diaphragm, Floating Element 

For which Fluid do You Use the Flow Meter?

Chemical and physical properties of the medium can influence the material of the flow meter and therefore how the instrument works. Commonly, these wetted parts (parts that are exposed to or in direct contact with the medium) may be offered:

• aluminum
• stainless steel
• hastelloy
• monel in combination with Viton (FKM), Kalrez (FFKM), or EPDM elastomer seals

Please note that MEMS or CMOS (chip) sensors, which are applied in some gas flow meters, are only suitable for a restricted number of non-aggressive gas types. Another aspect you must consider is the viscosity of the fluid, the density, and dispersion (solid content). Not all measurement technologies can be used for all fluids.

What is the Flow Rate?

The flow rate is usually the most important specification to consider when selecting a flow meter. Fluid quantity can be displayed in volume, standardized volume, and true mass units. The flow rate is the quantity of fluid per unit time flowing through a measuring device. 

It is important to know what reference conditions you are working with. A supplier usually indicates the minimum and maximum full scale range of a product series. This should meet your process requirements.  

What is the Inlet and Outlet Pressure?

When selecting a flow meter, it is important to know if you need a low pressure drop or not. The pressure drop is defined as the difference between the inlet and the outlet pressure. Next to this, flow meters have a maximum operating pressure. If you have a high-pressure application, you need to take this pressure rating into consideration. In case of mass flow control, the inlet pressure (P1) and outlet pressure (P2) are required for selection and dimensioning of the most appropriate control valve.

What is the Ambient Temperature and the Temperature of the Fluid?

The temperature of your fluid and of the instrument’s environment are the next topics on the list to check. Variations in fluid temperature may affect the accuracy of your measurement. In case of temperature fluctuations, it could be useful to select a flow meter with temperature compensation such as the EL-FLOW Prestige.

Too high or too low environmental temperatures may also harm the electronic components of your flow meter during operation or storage. When you use a flow meter in a furnace, burner, or in areas with very low temperatures, it’s important to check whether the instrument can withstand these extreme temperatures. Therefore, check the temperature specifications as provided by the supplier before selecting your flow meter.

4. What do You Want to Achieve with Your Flow Meter?

When selecting your flow meter, you need to think of what is important in your process. What do you want to achieve?

Performance versus Price  

The most common criteria to select a flow meter are price and performance. If you place price at the top of your criteria, you are likely to get a basic instrument with less than average performance.  Next to the price of the component, installation, maintenance, and repairs over time should be included in calculating the total cost of ownership. How much the meter costs to operate, like its electrical consumption, can also increase the overall cost of the flow meter. 

Flow Meter Repeatability

Repeatability is producing the same outcome given the same conditions. In other words, a flow meter should produce the same readings when operated under the same variables and conditions. This, too, is expressed as a ± percentage. For example, especially important for burner applications. 

Flexible Use

Sometimes it makes sense to select a flow meter that can be used in multiple applications. For instance, when you need an instrument in a research project and you know that other projects will follow in the future, but you have no idea what fluids will be used then. In cases like this, it can be beneficial to select a flow meter that is fluid independent and has a wide flow range as well such as Mini CORI-FLOW from Bronkhorst.

In case you have an application with high fluctuations in flow rate, you probably prefer a flow meter with a high turndown ratio. Turndown ratio is also commonly referred to as rangeability. It indicates the range in which a flow meter or controller can accurately measure the fluid. In other words, it’s simply the high end of a measurement range compared to the low end, expressed in a ratio and is calculated using a simple formula: Turndown Ratio = maximum flow / minimum flow.

5. Which Process Conditions can be Relevant?

Cleaning

In the food and beverage and pharmaceutical industry, cleaning your instrumentation is important to avoid cross contamination. Clean-in-place (CIP) is a method of cleaning the interior surfaces of pipes, vessels, equipment, filters, and fittings. A typical CIP cycle consists of various steps including washing with a hot cleaning agent and hot acid with temperatures up to 200˚F. 

Steam-in-place, also referred to as sterilization-in-place (SIP), consists of a phase in which the instrument is sterilized with saturated steam with a temperature up to 284 °F. Not all flow meters are suitable for these cleaning methods, so it’s an important factor to consider when applicable. Please also note that these markets often require the application of FDA approved seals as well.

Available Space

Is space limited in your process? Then select a flow meter that is compact and does not require a straight run of pipe at the inlet or outlet. There are ultra compact flow meters on the market based on MEMS technology (e.g. the IQ+FLOW gas flow meter).

Type of Communication

Check whether you need a digital or analog flow meter. Besides that, you need to know what type of communication is used in your process. Popular types of fieldbus communication are Profinet, EtherCAT, CANopen, Ethernet/IP, and POWERLINK, but also the more established versions such as Modbus, Profibus, and DeviceNet can be integrated.

There is also the possibility of using a manufacturer’s own fieldbus communication, such as Bronkhorst’s FLOW-BUS. This has the advantage of a simple and cost-effective network setup that can be transferred to common interfaces such as RS232, Profinet, and Profibus. 

Moisture

Some flow meters are more sensitive to moisture or particles than others. Appropriate filtering to protect your instruments may be a good investment, saving costs for cleaning, repair, interruption of your process, and possibly also the waste of raw material or finished product.

6. Examples of Applications that Use Flow Meters

Flow meters are used in a wide variety of applications; here are some examples:

Top 6 Water Flow Meter Types and Maintenance

Oct 26 ,

What are the most common water flow meters? There are the six most common types of flow meters for measuring water:

Electromagnetic Flow Meters

These meters use Faraday’s law of electromagnetic induction to measure the flow rate of conductive fluids.

Electromagnetic flow meters are known for their high accuracy, available in various sizes, making them suitable for a wide range of pipe diameters. And since they have no moving parts, it reduces the need for maintenance.

They can come out in different materials of liners, electrodes, housing, making them highly resistant to corrosion and suitable for various water quality conditions.

Ultrasonic Flow Meters

Ultrasonic flow meters use ultrasonic waves to measure the flow velocity of water. They are non-invasive and can be mounted externally, making them suitable for a wide range of pipe sizes and applications, with no demand for pipe penetration and production stop. And the price will not change greatly for large DN sizes.

Turbine Flow Meters

Turbine flowmeters use a spinning rotor to measure flow rate. They are commonly used for water and other low-viscosity liquids. Turbine flow meters provide precise measurements and can measure a broad range of flow rates, from low to high.

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If you are looking for more details, kindly visit radar flow meter.

Vortex Flow Meters

Vortex flow meters use the principle of vortex shedding to measure flow rate. They provide high accuracy. With no moving parts in contact with the fluid, they are robust and require minimal maintenance, reducing downtime and operational costs. Vortex flow meters can handle a wide range of fluid types and temperatures, enhancing their versatility.

The above-mentioned four types are used to measure water in pipes, while to measure water flow in rivers, channels, we have these two options.

Radar Flow Meters

Radar flow meters utilize microwaves to measure flow. They send out radar signals that are reflected off the surface of the liquid or solid being measured. The time it takes for the signal to return is used to calculate the flow rate.

Radar flow meters do not come into direct contact with the fluid or solid, reducing the risk of contamination and minimizing maintenance requirements. They can handle a broad range of flow rates and are suitable for both high and low flow applications. With no moving parts, they require minimal upkeep, resulting in reduced downtime and lower operational costs.

Open Channel Flow Meters

Open channel flow meters are used to measure the flow of liquids in open channels like rivers, streams, or wastewater treatment channels. These meters typically use principles like weirs, flumes, or ultrasonic sensors to measure the flow rate based on the depth of the liquid and its velocity.

Open channel flow meters don’t interfere with the flow of the liquid and are non-intrusive. With no moving parts, they require minimal maintenance, which is especially beneficial in remote or challenging locations.

They are often a cost-effective solution for measuring flow in open channels and can be easily integrated into existing systems.

Below are the main parameters comparison for easy reference.

How to Maintain Water Flow Meters

Maintaining water flow meters is essential to ensure accurate and reliable measurements over time. Here’s a general guide on how to maintain water flow meters:

Regular Inspection

Periodically inspect the flow meter for physical damage, corrosion, or signs of wear. Replace any damaged components or seals.

Clean the Meter

Keep the flow meter clean from debris, sediment, or any buildup that may affect accuracy. Use a soft cloth or a gentle cleaning solution for this purpose.

Calibration

Schedule regular calibration checks to ensure the flow meter’s accuracy. The frequency of calibration depends on the type of flow meter and the specific application.

Check Seals and Gaskets

Inspect the seals, gaskets, and O-rings for leaks or wear. Replace them if necessary to maintain a watertight seal.

Electronics and Wiring

Examine the electronic components and wiring connections for signs of damage or corrosion. Ensure all electrical connections are secure.

Pressure and Temperature Checks

Verify that the pressure and temperature of the fluid being measured are within the specified operating range of the flow meter. Extreme conditions can affect accuracy.

Environmental Considerations

Consider the environmental conditions in which the flow meter operates. For instance, in cold climates, make sure the meter is protected from freezing, and in corrosive environments, use appropriate materials and coatings.

Manufacturer’s Recommendations

Follow the manufacturer’s specific maintenance guidelines

Conclusion

The choice of the appropriate flow meter depends on factors such as the application, fluid properties, accuracy requirements, and budget constraints. Selecting the right flow meter is crucial to obtaining accurate measurements in a given water flow application.

Ask our expert to select the most suitable water flowmeter for your project today.

Customer Cases

1. How Radar Flow Meter Used in Wireless Monitoring Solution

2. Ultrasonic Open Channel Flow Meter for Textile Industry

3. Why Our Singapore Customer Satisfied with Our Clamp on Water Flow Meters

4. Electromagnetic Flow Meter for Chemical Industry