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Difference between revisions of "Differential Pressure Flow Meters"
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Differential Pressure Flow Meters (view source)
Revision as of 23:53, 23 March 2013
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[[Category:Meters, Gauges]]{{Knoppen}} | [[Category:Meters, Gauges]]{{Knoppen}} | ||
[[File:Differential Pressure Flow Meters.jpg|thumb|right| Differential Pressure Flow Meters]] | [[File:Differential Pressure Flow Meters.jpg|thumb|right| Differential Pressure Flow Meters]] | ||
[[File:Differential Pressure Flow Meters1.jpg|thumb|right| Differential Pressure Flow Meters]] | [[File:Differential Pressure Flow Meters1.jpg|thumb|right| Differential Pressure Flow Meters]] | ||
'''Differential Pressure Flow Meters'''are also known as head type flow meters. They are the most prevalent type of flow meters in use today. It has been projected that more than 50 percent of all liquid flow measurement applications make use of this type of unit. The basic working principle of differential pressure flow meters is based upon the Bernoullis equation | '''Differential Pressure Flow Meters''' are also known as head type flow meters. They are the most prevalent type of flow meters in use today. It has been projected that more than 50 percent of all liquid flow measurement applications make use of this type of unit. The basic working principle of differential pressure flow meters is based upon the Bernoullis equation | ||
which states the fact that the pressure drop across the meter is directly proportional to the square of the flow rate. The flow rate is calculated by measuring the pressure differential and extracting its square root. | which states the fact that the pressure drop across the meter is directly proportional to the square of the flow rate. The flow rate is calculated by measuring the pressure differential and extracting its square root. | ||
==Basic Elements== | ==Basic Elements== | ||
Differential pressure flowmeters consist of two elements. | Differential pressure flowmeters consist of two elements. | ||
===Primary element=== | ===Primary element=== | ||
This element causes a change in kinetic energy which results in the differential pressure in the pipe. The unit must be suitably matched to the | This element causes a change in kinetic energy which results in the differential pressure in the pipe. The unit must be suitably matched to the | ||
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* liquid's properties | * liquid's properties | ||
Besides, the measurement accuracy of the element must be fine over a practical range. | Besides, the measurement accuracy of the element must be fine over a practical range. | ||
===Secondary element=== | ===Secondary element=== | ||
The secondary element measures the differential pressure created by primary element and gives the signal or read-out which is in turn transformed to the actual flow value. | The secondary element measures the differential pressure created by primary element and gives the signal or read-out which is in turn transformed to the actual flow value. | ||
==Types of differential pressure flow meters== | ==Types of differential pressure flow meters== | ||
Most widely used differential pressure flowmeters are: | Most widely used differential pressure flowmeters are: | ||
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* Venturi tubes | * Venturi tubes | ||
* Variable area flowmeters, i.e. Rotameters | * Variable area flowmeters, i.e. Rotameters | ||
==Errors and Noise== | ==Errors and Noise== | ||
In case of compressible fluids, the ratio of differential pressure divided by upstream pressure should not exceed 0.25 for reduction of error and correction of density. Metering errors caused due to wrong installation of the primary element can become considerable i.e. up to 10%. Following are the possible causes of these errors: | In case of compressible fluids, the ratio of differential pressure divided by upstream pressure should not exceed 0.25 for reduction of error and correction of density. Metering errors caused due to wrong installation of the primary element can become considerable i.e. up to 10%. Following are the possible causes of these errors: | ||