Mass Flow Meters – Basic Principles Of Mass Flow Measurement

Mass flow meters are used in many applications where there is a need for repeatable and accurate readings and to determine the mass of any flow of liquid, gas or air. They are generally used to monitor the flow of the particular substance to gauge the operational efficiency of certain machines or processes. These machines and processes are found in many industries from chemical engineering, semi conductor fabrication, water control and production of heavy machinery. This article will explain the basic principles of the mass flow meter.

Flow metering is the application of measuring the flow of a substance or medium. A meter has to have the following qualities :

• Repeatability – can the device repeat the same result or flowrate repeatedly under the same circumstances.
• Uncertainty – As it is impossible to get the exact mass flow rate, the uncertainty is a ratio of probable accuracy.
• Accuracy – the correct flowrate as a relative value to a highly calibrated procedure when setting up the flow meter.
• Turndown – the turndown or turndown ratio is the range of flowrate or mass under which the flow meter will return repeatable and accurate results. The tolerance of the meter.

There are two technologies that underpin how a mass flow meter works. These are thermal dispersion and the Coriolis effect. The thermal dispersion technology is used for measuring the mass of gases and air. The Coriolis flow meters are used for liquids.

Thermal dispersion mass flow meters work by having two sensors, known as resistance temperature detectors or RTD's. One RTD is kept at a constant temperature by an external heat source. The other has the media or gas passed over it. This influences the temperature of the sensor. As the mass flow increases the temperature of the sense changes. By determining the differential change between the two sensors the mass flow rate can be determined.

The coriolis or inertial flow meter is a separate pipe from the rest of the machine or process technology. When a fluid mass passes into the inlet part of the pipe it exerts a force on that part of the pipe causing it to move or vibrate. As it leaves the pipe via the outlet, it exerts an opposite force causing that part of the pipe to vibrate at a different frequency. By mapping the change in frequency from inlet to oulet the mass flow of the liquid can be determined.

Uses of Mass Flow Meters 

mass flow meters can be small so that they work in car engines, or even smaller engines like lawn mower engines. they are also used in many heavy machinery in large industrial industries like the petroleum industry or water management. A mass flow meter can save money on a grand scale by revealing exactly how much fluid is passing through the tubes of the small car engine or the machinery at large water reclamation plants.