Instrumentation

Flow transmitter


In this lesson, we will discuss the flow transmitter. A flow transmitter is a differential pressure transmitter.

For creating differential pressure in the flow transmitter we use a flow orifice.


Flow transmitter

Differential pressure flow transmitters use Bernoulli’s equation to measure the flow of fluid in a pipe. Differential pressure flow transmitters introduce a constriction in the pipe that creates a pressure drop across the flow transmitters. When the flow increases, more pressure drop is created. Impulse piping routes the upstream and downstream pressures to the transmitter that measures the differential pressure to determine the fluid flow. Bernoulli’s equation states that the pressure drop across the constriction is proportional to the square of the flow rate. Using this relationship, 10 percent of full scale flow produces only 1 percent of the full scale differential pressure.

Flow transmitter or differential pressure transmitter
Flow transmitter

In an industry flow nozzle, low-loss flow tube are also used for flow measurements.
Differential pressure flow transmitters measure the flow of liquids, gases and vapor, such as water, cryogenic liquids, chemicals, industrial gases, and steam.

The relationship between the differential pressure and flow rate is derived from Bernoulli’s equation. Using Bernoulli’s equation, and conservation of square of mass , it can be shown that the differential pressure generated is proportional to the square of the mass flow rate, Qm (kg/s).
ΔP ∝ Qm^2
Industries Where Used
Differential pressure flow transmitters are generally applicable to many flows in most industries.the industries are such as mining, mineral processing, pulp and paper, petroleum, chemical, petrochemical, water, and wastewater industries. Other flow measurement technologies may perform better than differential pressure flow transmitters in many applications but differential pressure flow Transmitters are still used extensively because of long-standing user familiarity with the technology.

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