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M ass Flow Sensors

M ass Flow Sensors. A process cannot be understood by stopping it. Understanding must move with the flow of the process, must join it, must flow with it. Muhammad Usman Afzal (07-chem-33). Synopsis. Flow measurement Selection criteria Types of flow sensor References.

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M ass Flow Sensors

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  1. Mass Flow Sensors A process cannot be understood by stopping it. Understanding must move with the flow of the process, must join it, must flow with it. Muhammad UsmanAfzal (07-chem-33)

  2. Synopsis • Flow measurement • Selection criteria • Types of flow sensor • References

  3. Flow Measurement • Flow sensors Flow sensors are devices for sensing the rate of fluid flow whether it be a gas, steam, liquid.

  4. Selection criteria • Flowing media • Accuracy sensitivity and precision • Local or remote display • Working range (span) • Area of installation • Flow measurement type • Process conditions

  5. Types of Flow Sensor

  6. (A)Mass Air Flow Sensors • A mass air flow (MAF) sensor responds to the amount of fluid (usually a gas) flowing through a area containing the sensor. It is supposed to be insensitive to the density of the fluid.

  7. Types of MAF

  8. Vane Meter Sensor • Rotating vane • Count the rotations • Connect it to the electric circuit • Wright’s spirometer

  9. Drawbacks with VMS • It restricts air flow which limits engine output. • The moving electrical or mechanical parts can wear. • Finding a suitable mounting location within a confined engine compartment is problematic.

  10. Hot Wire Sensor • Electrical resistance function of temperature • Temperature is again increased to establish a equilibrium

  11. Advantages with HWS • Responds very quickly to changes in air flow. • Low air flow restriction. • Less sensitive to mounting location and orientation. • No moving parts improve its durability. • Less expensive. • Separate temperature and pressure sensors are not required.

  12. Drawbacks with HWS • Dirt and oil can contaminate the hot-wire deteriorating its accuracy. • Installation requires a laminar flow across the hot-wire

  13. Cold Wire Sensor • The inductance of a small sensor changes with the air mass flow over that sensor. • An oscillatory circuit whose oscillation frequency changes with sensor inductance • Frequency is related to the amount of air passing over the sensor.

  14. Pneumotachograph • Pressure drop across the resistance

  15. (B)Turbine Sensors • A propeller is placed in the path of the fluid or gas. • Frequency based output signals

  16. (C)ElectromagneticSensor • Faraday law of electromagnetic induction is the basic principle.

  17. (D)Thermal Transport Sensor • Replacement for marking the flowing media

  18. (E)Drag ForceSensor • Used for high turbulence (wind flow rate)

  19. References • Jacob Fraden, “Handbook of modern sensors”, Ed. 3rd , chapter 11, page 361-379 • http://www.frca.co.uk/article.aspx?articleid=100390 [11/05/2010] • http://www.worldlingo.com/ma/enwiki/en/Mass_flow_sensor [11/07/2010] • http://www.reference.com/browse/Mass_flow_sensor [12/13/2010]

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