There are countless types of flow meters available—how do you choose the right one? This article is designed to address the challenges users face when purchasing flow meters, helping readers select the most suitable one for their needs!
Before You Buy: What Are the Types of Flow Meters?
To meet various application needs, the market offers a wide range of flow meters. However, they can be broadly categorized based on their measurement principles. Here are 10 common types:
This article focuses on the steps to selecting a flow meter, guiding readers to understand the characteristics and application conditions of 10 types of flow meters to assist with preliminary selection. The content is primarily designed for readers who are less familiar with flow meters. If you already have a basic understanding, it is recommended to contact manufacturers directly for further consultation and purchasing advice. For a deeper dive into how flow meters work, please refer to "
Understand How Different Flow Meters Operate in 5 Minutes."
Steps for Selecting a Flow Meter
1. Flow Meter Fluid Medium
When selecting a flow meter, the first step is to determine what medium needs to be measured. Are you purchasing a flow meter for liquids or gases? Since different flow meters operate on distinct measurement principles, not all are suitable for both liquids and gases.
Additionally, it is recommended to provide manufacturers with detailed information about the liquid or pipeline before purchasing. This includes factors such as the liquid's pH level, whether the pipe is full, the presence of bubbles, and the liquid's viscosity. These details will help ensure you choose the most suitable flow meter.
➤ Flow Meter Fluid Medium Reference Table:
Flow Meter Type
|
Liquid |
Gas |
| 1. Ultrasonic Flow Meter |
✔ |
✔ |
| 2. Paddle Wheel Flow Meter |
✔ |
✘ |
| 3. Variable Area Flow Meter (Rotameter) |
✔ |
✔ |
| 4. Coriolis Flow Meter |
✔ |
✔ |
| 5. Positive Displacement Flow Meter (Gear Flow Meter) |
✔ |
✘ |
| 6. Vortex Flow Meter |
✔ |
✔ |
| 7. Turbine Flow Meter |
✔ |
✘ |
| 8. Differential Pressure Flow Meter |
✔ |
✔ |
| 9. Electromagnetic Flow Meter |
✔ |
✘ |
| 10. Thermal Mass Flow Meter |
✔ |
✔ |
2. Pipeline Pressure Rating and Temperature Range
Pipeline pressure and temperature are also crucial considerations when selecting a flow meter. Different flow meters have varying levels of pressure and temperature resistance. Even within the same type of flow meter, the tolerance may vary due to differences in material or special design requirements.
In engineering design, it is generally recommended to add a safety margin of 10 units. For example, if the liquid inside the pipe is at a temperature of 50°C and the pressure is 20 kg/cm², the flow meter should ideally have a temperature tolerance of at least 60°C (50 + 10) and a pressure resistance of at least 30 kg/cm² (20 + 10) to ensure safety.
Pipeline pressure and temperature are also crucial considerations when selecting a flow meter. Different flow meters have varying levels of pressure and temperature resistance. Even within the same type of flow meter, the tolerance may vary due to differences in material or special design requirements.
In engineering design, it is generally recommended to add a safety margin of 10 units. For example, if the liquid inside the pipe is at a temperature of 50°C and the pressure is 20 kg/cm², the flow meter should ideally have a temperature tolerance of at least 60°C (50 + 10) and a pressure resistance of at least 30 kg/cm² (20 + 10) to ensure safety.
➤ Reference Table for Flow Meter Pressure Range and Operating Temperature:
Compiled from the official websites of flow meter manufacturers like Emerson, Endress+Hauser, and Doweston:
Pressure is measured in MPa:
Low Pressure: ≤ 1.0 MPa
Medium Pressure: 1.0 MPa to 10 MPa
High Pressure: > 10 MPa
➤ Temperature inside the pipe is measured in degrees Celsius (°C):
Low Temperature: -40°C to 0°C
Medium Temperature: 0°C to 100°C
High Temperature: > 100°C
Flow Meter Type
|
Pressure Range
|
Fluid Temperature Inside Pipe |
| 1. Ultrasonic Flow Meter |
High (installed outside the pipe, no pressure limit) |
Low to High |
| 2. Paddle Wheel Flow Meter |
Low |
Medium |
| 3. Variable Area Flow Meter (Rotameter) |
Low |
Medium |
| 4. Coriolis Flow Meter |
Medium |
Low to High |
| 5. Positive Displacement Flow Meter (Gear Flow Meter) |
Medium |
Low to Medium |
| 6. Vortex Flow Meter |
Medium |
Low to High |
| 7. Turbine Flow Meter |
Medium |
Low to Medium |
| 8. Differential Pressure Flow Meter |
High |
Low to High |
| 9. Electromagnetic Flow Meter |
Medium |
Medium |
| 10. Thermal Mass Flow Meter |
Low to Medium |
Low to High |
3. Flow Meter Measurement Range
The measurable range of the flow meter should exceed the fluctuation range of the liquid flow within the equipment pipeline.
It is advisable to choose a flow meter with a range that meets your needs. For example, if the equipment's measurement range is between 20–100 LPM, dividing 100 by 20 gives a ratio of 5. In this case, selecting a flow meter with a range greater than 1:5 is recommended.
Additionally, the minimum measurable flow of the flow meter should be less than 20 LPM, and the maximum measurable flow should exceed 100 LPM. For instance, you could choose a flow meter with a range of 15–150 LPM or 10–200 LPM.
The minimum range (lower limit) of the measurement range affects the zero point (boundary value), while the upper limit impacts the accuracy of the flow meter. This is because errors are typically calculated as a percentage of the upper limit (full scale). Therefore, if the interval between the minimum and maximum measurement values is too large, the accuracy at lower flow rates will generally be poorer.
➤ Reference Table for Flow Meter Measurement Ranges:
High Range Ratio: > 1:50
Suitable for applications requiring measurement of both extremely small and large flow rates.
Medium Range Ratio: Between 1:20 and 1:50
Ideal for most industrial applications.
Low Range Ratio: < 1:20
Best for applications with a narrow flow range and relatively stable flow rates.
4. Accuracy Requirements for Flow Meters
While accuracy is important, higher accuracy typically comes with a higher price. It is recommended to balance accuracy and cost based on your needs. For example:
If you only want to estimate the amount of tap water flowing through a pipeline, a flow meter with high accuracy is not necessary.
For applications like monitoring chemical agents in precision processes, a liquid flow meter with higher accuracy is essential.
Below, let's explore some key terms related to flow meter accuracy:
1) Repeatability and Measurement Accuracy
Repeatability
Definition: The consistency or closeness of measurement results when measuring the same quantity multiple times under identical conditions. Repeatability reflects the stability of the measuring device or system over multiple measurements in a short period.
Example: Suppose you use a water flow meter to measure the same flow rate (e.g., 10 liters per second) and repeat the measurement 10 times under identical conditions. If the flow meter has high repeatability, the results will be very close to each other, such as 9.98, 9.99, and 10.01 liters. The higher the repeatability, the smaller the data dispersion.
Measurement Accuracy
Definition: The closeness of a measured value to the true value (or reference standard). Measurement accuracy reflects the correctness of the measuring device.
Example: If you are measuring a liquid flow rate of 10 liters per second, an ideal flow meter should display exactly 10.0 liters per second. If the flow meter shows 9.8 liters per second, it indicates lower measurement accuracy. The higher the measurement accuracy of the flow meter, the closer the measured value is to the true value of 10.0 liters per second.
2. Full Scale (FS) vs. Reading (Rd) Accuracy in Flow Meters
When reviewing the accuracy specifications of a flow meter, it is important to note whether the accuracy is expressed as a percentage of Full Scale (FS) or a percentage of the Reading (Rd or RD).
1) What Is Full Scale (FS)?
When using Full Scale (FS) to represent error, the error is calculated based on the maximum range of the flow meter. The absolute error remains constant, but the relative error as a percentage of the actual flow rate varies depending on the flow rate.
Example: If a flow meter with a maximum range of 100 liters per second has an accuracy of ±1% FS, the absolute error is always ±1 liter per second, regardless of the actual flow rate.
At 100 L/s, the relative error is ±1%.
At 50 L/s, the relative error increases to ±2%.
At 10 L/s, the relative error becomes ±10%.
The advantage of expressing error as Full Scale (FS) is its simplicity and ease of calculation, as the absolute error is based on the full scale and remains constant. However, as the flow rate decreases, the proportion of absolute error to the flow rate (relative error) becomes significantly larger, leading to reduced measurement accuracy.
2) What Is Reading (Rd or RD)?
When using Reading (Rd or RD) to express error, the error is calculated based on the actual measured value. Regardless of where the flow rate falls within the measurement range, the percentage is always derived from the current reading.
Example: If a flow meter has an accuracy of ±1% Rd and measures a flow rate of 50 liters per second, the absolute error is ±0.5 liters per second. At a flow rate of 10 liters per second, the absolute error decreases to ±0.1 liters per second.
The advantage of using Reading (RD) to express error is that the error varies with the measured value, allowing for greater precision at low flow rates and a stable relative error. This makes it ideal for applications with fluctuating flow rates, as it maintains accuracy across a wide range.
However, its downside is that calculations are more complex, requiring dynamic computation for each reading. Additionally, at higher flow rates, the absolute error may increase, potentially reducing the accuracy of high-flow measurements.
➤ Flow Meter Accuracy Reference Table
Based on product data from manufacturers such as Emerson, Endress+Hauser, and Doweston, the following accuracy levels are classified using Full Scale (FS) error as the standard:
High Accuracy: FS ≤ ±0.5%
Suitable for laboratory measurements or high-precision industrial applications.
Accuracy: FS between ±0.5% and ±2%
Ideal for most industrial applications and routine measurement needs.
Low Accuracy: FS > ±2%
Suitable for applications with significant flow variations or low precision requirements.
5. Installation Environment for Flow Meters
When selecting a flow meter, it is essential to consider whether the equipment can or should involve pipe cutting, as well as the installation location:
Determine if the system can be stopped and the pipe cut for installation:
If the pipeline cannot be shut down or cut, a non-invasive flow meter, such as an ultrasonic flow meter, is recommended. However, installing a flow meter without cutting the pipe generally requires a higher budget.
Choose the appropriate connection method based on pipe material:
Proper connection methods enhance the sealing of the flow meter.
Metal pipelines (e.g., stainless steel, copper): Typically require welding or flange connections.
Plastic pipelines (e.g., PVC, PPH): Usually use adhesive or threaded joints.
Consider corrosion resistance needs:
If the fluid is corrosive, choose flow meters made of materials with high chemical resistance, such as PVC, PPH, PVDF, or PFA.
Pay attention to the installation position—horizontal or vertical?
Ensure the selected flow meter can be effectively installed in the intended orientation for optimal performance.
Horizontal or vertical measurement also involves specific considerations during installation, so it’s important to choose the right flow meter based on site conditions.
For horizontal pipelines:
It is best to install the flow meter at a low point, such as the bottom of a U-shaped pipe. Installing at higher positions may result in insufficient pressure, causing the liquid to not fully fill the pipe, which can lead to inaccurate flow measurements.
For vertical pipelines:
It is recommended to install the flow meter on a section where the liquid flows upward (from bottom to top). This is because when the liquid flows downward (from top to bottom), it may fall in segments, leading to unstable flow velocity. Installing the flow meter on an upward-flowing section ensures more consistent and accurate measurements.
6. Flow Meter Acquisition Cost and Special Certifications
When purchasing a flow meter, it is essential to consider not only the cost of the device itself but also the installation, maintenance, and operational expenses. For instance, while electronic flow meters have a long service life, they require periodic calibration to maintain accuracy.
Moreover, check whether the flow meter must meet specific certification requirements, particularly in industrial environments with high safety and explosion-proof standards. Examples of special certifications include:
➤Based on price ranges observed on e-commerce platforms such as Amazon and Alibaba, using DN25 (1 inch) as the standard:
High Cost: Over $1200
Medium Cost: $600–$1200
Low Cost: Below $600
7. Signal Transmission in Flow Meters
In some scenarios, there is a need for flow data storage and transmission. Additionally, in recent years, the Energy Management Act has mandated that buildings and workplaces conduct annual energy reporting, requiring flow meters with data collection capabilities.
When purchasing a flow meter, it’s crucial to ensure compatibility with communication interfaces and protocols. Check the flow meter catalog provided by manufacturers to confirm the communication modes.
For more information on communication modes, explore these resources:
8. Summary of Flow Meter Features
| Classification Criteria |
Pressure (MPa) |
Temperature (°C) |
Range Ratio |
Accuracy (FS) |
Cost (USD) |
| High |
> 10 MPa |
> 100°C |
> 1:50 |
≤ ±0.5% |
> 1200 |
| Medium |
1.0 MPa to 10 MPa |
0°C to 100°C |
1:20 to 1:50 |
±0.5% to ±2% |
600 ~ 1200 |
| Low |
≤ 1.0 MPa |
-40°C to 0°C |
< 1:20 |
> ±2% |
< 1200 |
▸ Detailed model information referenced in this article:
Ultrasonic Flow Meters: LORRIC FU-ES, KEYENCE FD-Q, EMERSON Flexim FLUXUS H721, Endress-Hauser Proline Prosonic Flow 91W; Paddle Wheel Flow Meters: LORRIC FP-AS510 P025, FineTek EPR; Rotameters: LORRIC F301, SinJin H-100; Coriolis Flow Meters: Doweston FTM-1600F, Endress-Hauser Proline Promass F 300; Positive Displacement Flow Meters: Doweston FTC-1600; Vortex Flow Meters: Doweston FTV-1600S, EMERSON Rosemount 8600; Turbine Flow Meters: Doweston FTR-1600R; Differential Pressure Flow Meters: Doweston PD-750W, EMERSON 3051SFA; Electromagnetic Flow Meters: Doweston FTE-1600S, Endress-Hauser Proline Promag W 400; Thermal Mass Flow Meters: Doweston FTW-1600T, Endress-Hauser Proline t-mass A 150
We hope the above information helps readers choose the right flow meter. With 30 years of expertise in the fluid field, LORRIC is dedicated to providing reliable products and services. We offer a wide range of flow meters for selection. You can click on the flow meter names in the table above to visit their respective product pages for more details. If you have any other purchasing or technical-related questions, feel free to leave us a message on Contact Us!