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Mass Flow Meter Measuring Principle


How Does a Mass Flow Meter Work?

The ability a flow meter to accurately measure and control flow is essential in maintaining the process conditions required to maximize plant production, efficiency and product quality.  Oftentimes, flow measurements are used as indicators of overall process performance.  This is due to the law of conservation of mass which states that the mass entering a system is equal to the mass leaving the system when both are measured over the same interval.  Therefore, mass flow meters and mass flow transmitters become crucial in overall plant operations.

The relationship between mass flow and volumetric flow is as follows: Mass Flow Rate = Density x Volumetric Flow Rate

Although volumetric flow under nominal conditions may be accurately calculated, the process conditions and fluid properties can vary sufficiently such that it is questionable if the measured volumetric flow rate (or derived using velocity) represents the required mass flow rates.  Process conditions such as density and viscosity, and their effect on the accuracy of flow measurement must be taken under consideration. The effects of temperature on density of fluids vary widely.  Gases and steam are most affected while solids are least affected, and liquids generally range somewhere in between.  The effects of pressure on the density of solids are negligible because both are non-compressible.  However, liquids requiring higher accuracies (better than ±1%) such as fuel monitoring, mass balancing of liquids and others require liquid mass flow meters.  Please go to Industrial Measurement Applications for applications requiring Coriolis flow meters. However, the effect of pressure on the density of gases and steam is considerable.  The SmartMeasurement™ ATMF family of thermal mass flowmeters for gases are ideal for accurately monitoring mass flow of gases, while our ALVT-mass flow meters are ideal for direct steam flow meter measurement.

Direct mass flow measurement vs indirect mass flow measurement

Indirect mass flow measurement

Flow meters such as Magnetic, Ultrasonic, Differential pressure, Positive Displacement, Variable Area, non-compensated Vortex and Turbine meters are strictly volumetric flow meters.  However often times, these flowmeters are combined with pressure & temperature measurement and a flow computer to measure mass flow.  These are indirect mass flow meters because one must have several types of sensors as well as a computer to calculate mass flow.  Indirect mass flow measurement is usually used to measure mass flow because often direct mass flow measurement cannot satisfy some application parameters. However, SmartMeasurement™ has direct mass flow solutions for any application.

Direct mass flow measurement of Gases

SmartMeasurement‘s ATMF thermal mass flow family has the ability to measure mass flow of gases directly without the use of other equipment to measure mass flow.

Direct mass flow measurement of Liquids

SmartMeasurement‘s ALCM Coriolis flow meter family has the ability to measure mass flow of liquids directly without the use of other equipment to determine mass flow.

Direct mass flow measurement of Liquids

SmartMeasurement‘s ALVTN vortex flow meter family has the ability to measure mass flow of steam directly without the use of other equipment to measure mass flow.  Our mass flow vortex flow meter has an integrated temperature and pressure sensor as well as a mass flow transmitter.  Vortex flow meters are ideal for steam flow measurement because other mass flow meters or volumetric flow meters cannot measure steam.  Differential pressure techniques can be used for indirect mass flow measurement of steam, but as mentioned above, direct mass flow measurements are much better than indirect mass flow measurement.