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Measuring technique for flow rate measurement

Flow rate measuring instruments measure the amount of substance that flows through a pipe cross-section per time unit. The measured quantity is outputted as mass or volume. Typical flow rate applications measure gases, vapours and aggressive or viscous liquids in pipelines as well as bulk solids on conveyor belts.
VEGA uses two different physical measuring principles for flow rate measurement:
  • Differential pressure
  • Radiometric

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Measuring principles
Function
Application

Measuring technique for flow rate measurement

Differential pressure

VEGADIF: Flow-rate measurement via differential pressure
VEGADIF: Flow-rate measurement via differential pressure

Radiation-based

 WEIGHTRAC: Measurement of mass flow on conveyor belts with radiometric measuring principle
WEIGHTRAC: Measurement of mass flow on conveyor belts with radiometric measuring principle

Briefly explained: What is flow measurement?

Every day, a wide variety of substances are transported and distributed through tubes and pipelines. They can be liquids such as water, oils and gases or chemicals, or even slurries containing solids. In order to determine the quantity of a substance that flows through a pipe cross-section per unit of time, plant operators use a flow measuring system. The amount of substance is specified as mass or volume and recorded with special flow meters.

How are flow meters constructed?

A flow meter basically consists of two main components: a sensing element, which serves as a flow sensor, and a transducer, which converts and evaluates the measured values. The sensing element can gather qualitative or quantitative information on certain physical or chemical properties as well as the material composition of its environment. The transducer then converts this recorded information into appropriate values, which are then output as processable variables, usually in the form of electrical signals.

 

What measuring methods does VEGA use for flow measurement?

VEGA uses basically two different physical measuring principles for flow measurement: Differential pressure and radiometry. Measurement of flow via differential pressure operates by means of a differential pressure generator, e.g. an orifice plate or a dynamic pressure probe. A differential pressure transmitter calculates the flow rate from the measured value. Differential pressures of only a few mbar can be detected even if the basic static pressure is very high. Thanks to the very high resolution of the measuring cell and the very small deviation, precise flow measurements can be realised. What is more, the large selection of measuring ranges opens up a wide spectrum of applications for differential pressure measurement.

What areas of application are there for flow measurement?

Along with temperature, pressure and force, flow measurement is one of the most important parameters in industrial measurement engineering. Typical applications measure gases and steam, aggressive or viscous liquids as well as bulk solids on conveyor belts. Since all of these substances have very different properties, there are different methods for measuring them:  differential pressure and radiometry.

Mass flow determination on a conveyor belt

The measuring principle of radiometry, i.e. radiation-based measurement, is used, for example, to measure mass flow on conveyor belts . The process begins with an isotope emitting focussed gamma radiation. The sensor, located on the opposite side of the conveyor belt, picks up this radiation. The scintillator of the sensor converts the gamma radiation into signals, the number of which is recorded and evaluated. Because gamma rays are attenuated as they pass through matter, the sensor can calculate the mass flow based on the change in intensity in combination with the belt speed. One big advantage of radiometry is that it is wear and maintenance free, due to being a non-contact measuring method. The simple installation of the measuring system, for example around the frame of a conveyor belt system, as well as the simple setup and commissioning, are the other main advantages. These benefits make it ideal for achieving the goal of this application: reliable and exact determination of the conveyed quantity of solids.
And, radiometry can also be used to measure mass flow in pipelines. In this case, too, a source holder with a slightly radioactive isotope emitting gamma rays is deployed, mounted on one side of the pipe. The sensor on the opposite side of the pipe measures the intensity of the incoming radiation. The higher the density of the conveyed liquid, the less radiation received. Together with an input from a flow meter, the output signal can be used to calculate the mass flow from the measured density. A typical example is the mass flow of abrasive materials such as slurries.