What Is Turndown Ratio in Flow Meters? In simple terms, turndown ratio refers to the range of flow rates that a flow meter can accurately measure. This ratio is a crucial factor in selecting the right flow meter for your application, as it determines the meter’s ability to measure low and high flow rates with precision and accuracy.

Choosing a flow meter with a high turnover ratio can save you money and increase efficiency by eliminating the need for multiple flow meters or reducing maintenance and calibration costs. In this blog post, we will explore turnover ratio in flow meters, its importance, and how it impacts various industries.

RFQ Flow Meters
Turndown Ratio in Flow Meters

Definition of turndown ratio

So, what exactly is turndown ratio?

Well, it’s the measurement range of a flow meter from the highest to the lowest flow rate it can accurately measure. Essentially, it tells you how much the flow rate can be turned down or decreased while still maintaining accurate readings.

For example, a flow meter with a turndown ratio of 10:1 can accurately measure flow rates from 100 L/H down to 10 L/H.

This ratio is an important consideration when selecting a flow meter for your application, as it determines the meter’s versatility and ability to handle varying flow rates.

A higher turndown ratio means more flexibility and potentially cost savings, as you may not need multiple flow meters for different flow rates.

Why is Turndown Ratio important?

In flow measurement, the turndown ratio indicates the range of flow over which the flowmeter can measure with acceptable accuracy. It is also known as adjustable range. This is very important when selecting a flow meter technology for a specific application.

If the airflow to be measured is expected to vary between 100,000 cubic meters per day and 1,000,000 cubic meters per day. The turndown ratio for a specific application is then at least 10:1. Therefore, the meter requires at least a 10:1 turndown ratio.

What Is Turndown Ratio in Flow Meters

Formula for calculating Turndown Ratio

The turndown ratio can be expressed as:
TR = Q(max)/Q(min)

TR = Regulation Ratio
Q(max) = maximum flow
Q (min) = minimum flow

Example calculation

If the gas to be measured varies between 100000 m3/day and 1000000 m3/day.
This particular application has TR = 10:1.
The TR of the required flow meter should be at least 10:1
If the flow meter has a maximum flow rate of 2000000 m3/day, then the required turndown ratio (TR) will be 20:1

Typical turndown ratios for various flowmeters

The examples here are for gas flow, but the same gauge type can be used for liquids, with similar turndown ratios.

Different types of flow meters have varying turnover ratios. Here are some common flow meters and their typical turnover ratios:

It’s important to note that these are general ranges and actual turnover ratios may vary depending on the specific model, size, and operating conditions. When selecting a flow meter, it’s crucial to consider the turnover ratio and ensure that it can accurately measure the flow rate needed for your application.

T-series Triangle Coriolis Mass Flowmeter

T-series Triangle Coriolis Mass Flowmeter

Gear flow meter for Micro flow

Gear flow meter for Micro flow

Pointer Type Oval Gear Flow Meter

Magnetic Water Flow Meter

Choosing the right flow meter for your application

Selecting the right flow meter for your application is crucial to ensure accurate and precise measurements. Here are some key considerations when choosing a flow meter:

  • Flow rate range: Consider the expected flow rate range and select a flow meter with an appropriate turndown ratio.
  • Fluid properties: The properties of the fluid being measured, such as viscosity and corrosiveness, can affect the selection of a flow meter.
  • Environmental conditions: The operating environment, such as temperature and pressure, can impact flow meter performance.
  • Accuracy requirements: Consider the level of accuracy required for your application and select a flow meter that meets those requirements.

To maximize the turndown ratio of your flow meter, follow these best practices:

Proper installation: Ensure that the flow meter is installed correctly according to manufacturer specifications.

Regular calibration: Regular calibration of the flow meter is essential to maintain accuracy.

Maintenance: Proper maintenance of the flow meter, such as cleaning and inspection, can prolong its lifespan and improve performance.

Avoiding extremes: Avoid operating the flow meter at the extreme ends of its turndown ratio range, as accuracy may be compromised.

By considering these factors and following these best practices, you can select and maintain a flow meter that will provide accurate and reliable measurements for your application.

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In conclusion, turndown ratio is an essential factor to consider when selecting a flow meter for your application. It determines the range of flow rates that a flow meter can accurately measure, and a high turndown ratio can increase efficiency and potentially save you money.

Remember to consider the flow rate range, fluid properties, environmental conditions, and accuracy requirements when selecting a flow meter.

By following best practices such as proper installation, regular calibration, maintenance, and avoiding extremes, you can maximize the turndown ratio of your flow meter and ensure accurate and reliable measurements.

By selecting and maintaining the right flow meter, you can improve your operations and increase productivity.

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