With hundreds of flow meters available, how do you choose the right one? This article addresses the challenges users face when purchasing flow meters, introducing key considerations and summarizing the usage conditions of different types in a table. This will help you select the flow meter that best fits your needs. If you want to understand how flow meters work, please refer to Understanding How Different Flow Meters Work in 5 Minutes

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(This table is for preliminary selection reference only. Due to varying characteristics of flow meters from different manufacturers, it is recommended to refer to catalogs or consult manufacturers when purchasing to confirm whether the temperature and pressure resistance meet your usage conditions.)

&#; 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:Fluid temperature inside the pipe is measured in degrees Celsius (°C):

Moreover, pipe pressure and temperature are crucial. Different flow meters have varying tolerances to pressure and temperature. Even the same type of flow meter may have different resistance levels due to material differences or special design requirements. In engineering design, it's recommended to have a safety margin exceeding 10 degrees. For example, with a pipe pressure of 20 kg and sodium hydroxide solution at 50 degrees inside the pipe, using Lorric flow meters as an example, although the liquid temperature tolerance is greater than 50+10, the pipe pressure tolerance should be greater than 20+10.

(This table is for preliminary selection reference only. Due to varying characteristics of flow meters from different manufacturers, it's recommended to refer to catalogs or consult manufacturers to confirm if the flow meter's measurement range meets your usage conditions.)

&#; Reference Table for Measuring Ranges of Various Flow Meters:The following data is compiled from flow meter product information published on the official websites of manufacturers like Emerson, Endress+Hauser, and Doweston, based on the turndown ratio:

We can refer to the measuring range to select a flow meter that meets our needs. If the measurement range of the equipment is between 10-150 lpm, dividing 150 by 10 equals 15. It is recommended to choose a flow meter with a turndown ratio greater than 1:15. Additionally, it's advisable that the minimum measurable flow of the flow meter is less than 10 lpm, and the maximum flow is greater than 150 lpm. For example, you can choose a flow meter with a measuring range of 5~180 lpm or 3~300 lpm. The minimum value of the measuring range (lower limit) affects the zero point (boundary value); the upper limit affects the accuracy of the flow meter. Since errors are usually calculated as a percentage of the upper limit value (full scale), if there's a large gap between the minimum and maximum measurement values, the accuracy at low flow rates will be poorer.

The measurable range of the flow meter should be greater than the variation range of the liquid flow in the equipment pipeline:

While flow meter accuracy is important, higher accuracy often means a higher price. It's advisable to balance accuracy and cost based on your needs. For instance, if you just need to know the approximate flow in a pipeline, high accuracy isn't essential. However, for precise chemical monitoring in manufacturing processes, higher accuracy is crucial. Let's understand some related terms:

| Flow Meter Accuracy

1. Repeatability and Measurement Accuracy

Repeatability

Definition: The consistency or closeness of measurement results when the same quantity is measured multiple times under identical conditions. Repeatability reflects the short-term stability of the measuring device or system.
For example, if you use a flow meter to measure the same flow rate (e.g., 10 liters per second) and repeat the measurement 10 times under the same conditions, a flow meter with high repeatability will yield results very close to each other, such as 9.98, 9.99, 10.01 liters. Higher repeatability means less data dispersion.

Measurement Accuracy
Definition: The closeness of the measured value to the true value (or reference standard). Measurement accuracy reflects the correctness of the measuring device.
If you aim to measure a liquid flow of 10 liters per second, ideally, the flow meter should display 10.0 liters per second. If it shows 9.8 liters per second, it indicates lower measurement accuracy. The higher the measurement accuracy, the closer the measured value is to the true value of 10.0 liters per second.

2. Full Scale (FS) vs. Reading (Rd)

When you see the accuracy specifications of a flow meter, pay attention to whether it's expressed as a percentage of Full Scale (FS) or Reading (Rd or RD). 

1) What is Full Scale (FS)?

Using FS to express error means the error is calculated based on the maximum range of the scale. The absolute error remains constant, but the relative error percentage changes with the flow rate.

For example: Suppose a flow meter has a range of 3&#;300 LPM with an accuracy of ±3.0% FS.
Then, Absolute Error = 300 LPM × 3.0% = 9 LPM

If the displayed flow is 250 LPM, the actual flow could be 250 LPM ±9 LPM (241&#;259 LPM). The relative error is 9 LPM / 250 LPM = ±3.6%.

If the displayed flow is 100 LPM, the actual flow could be 100 LPM ±9 LPM (91&#;109 LPM). The relative error is ±9%.

The advantage of FS is that it's simple to calculate since the absolute error doesn't change. It's suitable for indicating errors at high flow rates. However, at lower flow rates, the absolute error constitutes a larger percentage of the flow rate, leading to poorer measurement accuracy.

 

2) What is Reading (Rd or RD)?
When using Rd to express error, the error is calculated based on the actual measured value. The percentage remains constant regardless of where the flow rate is within the range.

For example: Suppose a flow meter has an accuracy of ±0.3% Rd.

When the actual measured value is 100 LPM, the absolute error is 100 LPM × 0.3% = 0.3 LPM.

When the actual measured value is 50 LPM, the absolute error is 50 LPM × 0.3% = 0.15 LPM.

The advantage of Rd is that the error varies with the measured value, offering more precise measurements at low flow rates and stable relative errors. It's suitable for applications with varying flow rates, maintaining accuracy across different ranges. The downside is that calculations are more complex, requiring dynamic computation for each reading. At high flow rates, the error might increase, affecting measurement accuracy.

Based on data from manufacturers like Emerson, Endress+Hauser, and Doweston, using Full Scale (FS) error as the standard:

• High Accuracy: FS &#; ±0.5%, suitable for laboratory measurements or high-precision industrial applications.
• Medium Accuracy: FS between ±0.5% and ±2%, suitable for most industrial applications and daily measurement needs.
• Low Accuracy: FS > ±2%, suitable for applications with large flow variations or lower accuracy requirements.

&#; Flow Meter Accuracy Reference Table:Based on data from manufacturers like Emerson, Endress+Hauser, and Doweston, using Full Scale (FS) error as the standard:

Flow Meter Type

Accuracy Range

1. Ultrasonic Flow Meter

High

2. Paddle Wheel Flow Meter

Low

3. Variable Area Flow Meter (Rotameter)

Low

4. Coriolis Flow Meter

High

5. Positive Displacement Flow Meter (Gear Flow Meter)

Medium to High

6. Vortex Flow Meter

Medium

7. Turbine Flow Meter

Medium

8. Differential Pressure Flow Meter

High

9. Electromagnetic Flow Meter

High

10. Thermal Mass Flow Meter

High

(This table is for preliminary selection reference only. Due to varying characteristics of flow meters from different manufacturers, it is recommended to refer to catalogs or consult manufacturers to confirm if the flow meter's accuracy meets your usage conditions.)

V. Installation Environment

Whether the equipment can be shut down, whether pipe cutting is necessary, and the installation location must be considered when selecting a flow meter:

• Determine if the equipment can be shut down and pipes cut for flow meter installation: When the pipeline cannot be stopped or cut, it's recommended to use non-intrusive flow meters like ultrasonic flow meters, although installing without cutting the pipeline usually requires a higher budget.
• Select the connection method based on the pipe material: Choosing an appropriate connection method can enhance the sealing of the flow meter. Metal pipes (such as stainless steel, copper) usually require welding or flange connections, while plastic pipes (such as PVC, PPH) often use adhesive bonding or threaded connections.
• Pay attention to corrosion resistance requirements: When the fluid is corrosive, you need to choose flow meter materials with good chemical resistance, such as engineering plastics (PVC, PPH, PVDF, PFA).
• Note whether the installation position is horizontal or vertical?

 

There are considerations when installing on horizontal or vertical pipes; choose the flow meter based on site conditions. If installed on a horizontal pipe, it's best to install at a low point or the bottom of a U-shaped pipe, because insufficient pressure at higher points and incomplete filling of the pipe can lead to inaccurate flow measurements.

Contact us to discuss your requirements of Gas Flow Meters. Our experienced sales team can help you identify the options that best suit your needs.

If installed on a vertical pipe, it's recommended to install the flow meter where the liquid flows upward from bottom to top. If the liquid flows from top to bottom, it may create segmented falling flow, causing unstable flow rates. Therefore, install the flow meter on a pipe section where the liquid flows upward.

| Flow meter installed on a vertical pipe

VI. Purchase Cost and Special Certifications

When purchasing a flow meter, besides the price of the flow meter itself, you also need to consider installation, maintenance, and operating costs. For example, electronic flow meters have a long service life but may require periodic calibration.
Additionally, consider whether you have special certification requirements for the flow meter, especially in industrial environments with high safety and explosion-proof demands. Special certifications include:
CE: The European Union's safety, health, and environmental standards; all equipment sold in the EU must comply with these regulations.  
UL: U.S. safety certification, mainly for electrical safety and fire protection, widely used in the North American market.  
ATEX: European explosion-proof certification for explosive environments, applicable to high-risk areas like chemical and petroleum industries.  
Measurement Certification: Certification for flow meter accuracy and measurement compliance to ensure the accuracy of commercial measurements.

Based on price ranges of flow meters found on Amazon and Alibaba, using DN25 (1 inch) as the standard:

• High Cost: Above 15,000 TWD
• Medium Cost: 5,000~15,000 TWD
• Low Cost: Below 5,000 TWD

&#; Flow Meter Cost Reference Table:Based on price ranges of flow meters found on Amazon and Alibaba, using DN25 (1 inch) as the standard:

Flow Meter Type

Purchase Cost

1. Ultrasonic Flow Meter

Medium to High

2. Paddle Wheel Flow Meter

Medium

3. Variable Area Flow Meter (Rotameter)

Low

4. Coriolis Flow Meter

Medium

5. Positive Displacement Flow Meter (Gear Flow Meter)

Medium

6. Vortex Flow Meter

High

7. Turbine Flow Meter

Medium

8. Differential Pressure Flow Meter

Low

9. Electromagnetic Flow Meter

High

10. Thermal Mass Flow Meter

High

(This table is for initial selection reference only. Due to varying characteristics of flow meters from different manufacturers, it is recommended to consult catalogs or contact manufacturers to confirm whether the flow meter price meets your cost considerations.)

VII. Signal Transmission

For example, recent "Energy Management Act" regulations require equipment in buildings and workplaces to submit annual energy reports. This necessitates flow meters with data collection capabilities. When purchasing flow meters, pay attention to whether the communication interfaces and protocols are compatible.
Learn more:
&#; Ultrasonic Flow Meters Simplify Energy Reporting
&#; What Is Analog Current Output?
&#; What Is RS485?
&#; What Is a Switch Signal?

In some cases, there is a need for flow data storage and transmission. You should ensure that the signal transmission method is compatible with other equipment, such as Pulse, 4-20mA, RS485, I/O LINK, etc.For example, recent "Energy Management Act" regulations require equipment in buildings and workplaces to submit annual energy reports. This necessitates flow meters with data collection capabilities. When purchasing flow meters, pay attention to whether the communication interfaces and protocols are compatible.Learn more:

VIII. Summary of Various Flow Meter Features

4 Factors to Consider When choosing a Gas Flow Meter

A Quick Guide

Of all machines you&#;ve ever used or even the ones you&#;re yet to use, you&#;ll realize that none of them requires as much attention when selecting as a gas flow meter. You pick the wrong one and you&#;ll end up crying no matter how hard you try to make things work. Gas flow meters are usually designed and calibrated for different and specific needs.

You need to have some great knowledge about the things to look for when picking your next pack. For instance, some gas flow transmitters have been designed to work well under very low pressure while others can only perform best if the gas pressure is high enough.

It&#;s equally important to note that you can&#;t get all the things you want in one type of meter technology. Each type gas meters has got certain advantages and limitations. So, it&#;s just a matter of playing your cards right in order to end up with the one offering more advantages. Therefore, if you want an easy time, here are the four factors to consider when selecting a gas flow meter technology.

1. The Application for Which the Gas Flow Meter is meant

What are you going to use the gas flow meter for? Is your gas flow meter going to be put in Industrial, residential, or commercial applications? Answering these two questions accurately will be a huge win on your side. For example, not all gas flow meters can be used for custody transfers. There are specific ones that have been approved for this use.

Also, you could use the meter for measuring either mass flow or volumetric flow. This is very common in industrial applications. However, be reminded that gas flow meters for mass flow rate analysis will require additional devices for measuring temperature and pressure, however currently thermal mass flow meters does not require external temperature and pressure compensation to realize mass flow measurement, thermal flow meter is now more and more popular for gas flow measurement for its low price cost and easy installation. Coriolis mass flow meter can also detect gas mass flow , but the price cost is not low , also it is only for high pressure and high density gas flow measurement.

2. The Nature of the Gas you want to be Measured or Monitored

A gas can either be single or a mixture. But because single gases have got different thermal conductivity with the mixed gases, you must ensure that the gas flow meter you&#;re picking is calibrated according to your needs. You should also note that the gas flow sensors have been designed to operate within specific ranges of temperature and pressure. You know the range for the gases you want to measure &#; so, go for the right device to avoid getting incorrect readings.

3. The Location of Installation gas flow sensor

The site where you&#;re intending to install your gas flow meter comes with a number of other challenges which you must take care of. Keep in mind that environmental factors such as excess heat or coldness, and electric fields could greatly interfere with the performance of the gas meter. So, understand your site well so that you can pick the best device. You should also consider that you need to ensure enough straight pipelines to install gas flow meter sensor.

Apart from the environmental conditions, it&#;s advisable that you check if there are any government restrictions that might dictate the kind of a gas flow meter you should be operating. Ensure that what you have settled on meets all the regulations if there are any.

4. The Duration of Operation of the Meter

Gas flow meters can be operated on a long-term or short-term basis. However, you may also want a meter than can serve on both terms. Some of them have been designed to show total flow after a given period while others can show readings for broken periods. You must have a proper understanding of your meter&#;s calibration needs. Don&#;t just pick anything you come across.

Please note that the best thing you should always do is to read the user manual provided by the China flow meter manufacturer. Doing so will prevent cases of wrong installations and guarantee you the accuracy all the time.

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