There are more than 20 types of different flow transmitters. Unless the process engineer knows the advantages and disadvantages of each type, selectingflowmeter correctly can be a challenge.
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Flowmeter size and variety of measurement
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Chemical compatibility
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Process accuracy requirements
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Pressure requirements
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Acceptable pressure drop
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Cleaning requirements
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Desired measurement units
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Fluid viscosity limitations
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Necessary approvals for use in dangerous fields, sanitation, etc.
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Calibration and re-calibration requirements
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Maintenance issues
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Operating costs
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Connection styles (flanged, wafer, threaded, weld-on and so on)
Factors Relating to Flow meter 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. Fluid and flow characteristics:
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Nature of the fluid to be measured
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Liquid or Gaseous fluid used
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Corrosive fluid or other
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Is the fluid conductive or not?
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Does the slurry or big objects contain the fluid?
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viscosity of the fluid
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Will the 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.
4. Determine the variety of flow meters needed. Identify the minimum and maximum flows to be measured (mass or volumetric, depending on the application).
Accuracy:
The absolute accuracy is highly essential in instances where the flow meter is used for commercial purposes. Repeatability may be far more essential than accuracy for other applications, so it is advisable to set up individually for each flow meter implementation for accuracy and repeatability requirements.
It is also suggested that the user 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.
All accuracy statements are converted into uniform percentage of real reading units in correctly prepared flow meter specifications and these percentage of real reading demands are set individually for minimum, normal, and peak flows.
Flow meter accuracy comes in diffferent ways:
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Percentage of Flow Rate (% FR)
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Percentage of Calibrated Span (% CS)
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Percentage of Full Scale units (% FS)
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Percentage of Actual Reading (% AR)[/size]
Turndown ratio:
Some flowmeters provide the stated accuracy over a very restricted range, while others provide the stated accuracy over a very broad range.
Turndown ratio is simply the elevated end of the spectrum compared to the low end of the spectrum of measurement.