Flow Measurement

How to Select flow meter? Flow meter selection guide:

In an industrial plant, one of the most significant measurements is flow. How much of a fluid do you need to perform a specified job? Or how much petrol do you need to sell at the gas pump?

Whether you do the in-house selection of flow meters or a seller or contractor does the selection for you, there are many variables to consider effectively.

To select the right flow sensor or meter, you need to consider many important factors:

Application Requirements:

A clear and thorough knowledge of the demands of the specific implementation for which the flow sensor is designed is the foundation of a successful flow meter choice. Some of these criteria for implementation include:

  • Evaluate the nature of the process fluid and the overall installation
  • Flow rate information: is it continuous or totalized or both
  • Is the flow rate needed locally or remotely? If remotely, should the transmission be analog, digital or shared.
  • If shared, what is the minimum data update rate or frequency.

Factors effect to Flowmeter Operation:

We need to be able to analyze the properties and flow characteristics of the process fluid, the piping requirements that will accommodate the flow meter and many other operational factors in order to successfully select a flow meter that will be able to operate in the desired manner. These variables that should be closely regarded include:

1. Flow characteristics:
  • Nature of fluid
  • Liquid or gas fluid or slurry
  • Is the fluid is corrosive?
  • Is the fluid conductive or not?
  • Does the fluid contains slurry or large amount of solid substance.
  • viscosity of the fluid
  • fluid density or viscosity change

2. In relation to ordinary working values, minimum and maximum pressure and temperature expected.

3. Consider the piping and the region of installation or location of the flow meter. Specify the direction, size, material, timetable, flange (stress rating), accessibility, up or down stream turns, valves, controllers, and accessible straight-pipe run lengths for flow meter piping.

With regard to the region where the flow meter is installed, we must understand whether there are or are feasible vibration or magnetic fields, whether there is pneumatic or electrical power accessible, whether the area is categorized for explosion risks or if there are other unique conditions such as sanitary regulations.

4. Determine the required flow meter range. To accomplish this, identify the minimum and maximum flows (mass or volumetric depending on the application) that will be measured

5. Accuracy:

Determine the required flow measurement accuracy. Flow meter accuracy comes in different ways:

  • Percentage of Flow Rate (% FR)
  • Percentage of Calibrated Span (% CS)
  • Percentage of Full Scale units (% FS)
  • Percentage of Actual Reading (% AR)

The accuracy specifications should be indicated individually at the minimum, normal and maximum flow rates regardless of the accuracy metrics. Failure to do so may compromise your flow meter’s efficiency across its full range.

The absolute precision is highly essential in instances where the flow meter is used for business purposes (buying or selling). Repeatability may be far more essential than precision for other apps, so it is advisable to set up individually for each flow meter implementation for precision and repeatability requirements.

Care should be taken to properly interpret the accuracy of the flow meter. Flow meter accuracy can be inaccurate if misinterpreted. Meter accuracy in percentage flow rate, calibrated span of full-scale units all differ from minimum to maximum flow rate of the flow meter

The only proportion of real reading (percent AR) is the steady precision metric. Therefore, it is advisable to transform all cited error statements into the same percentage of real reading units in order to make a reasonable comparison in terms of precision between ranges of flow meter techniques in account for a specified implementation.

It is also suggested that the customer compare facilities of flow meters based on the complete flow loop mistake. Total inaccuracy is calculated by taking at the required flow rates the root of the sum of the component squares inaccuracies.

The above rules for the choice of flow meters are the fundamental minimum you should try to integrate into any specification and selection method for flow meters.


Instrumentation Engineer

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