What is a thermal mass flow meter?
Flow metering is the measurement of flow. A thermal mass flow meter is a device that measures gas mass flow based on the principle of convective heat transfer. These precision meters are widely used in various industries with a wide range of different applications. Those applications are grouped into energy conservation, environmental functions, industrial usage, and measurement by specified gas.
How do mass flowmeters operate?
A thermal mass flow meter measures gas flow based upon the principle of convective heat transfer. Either insertion style probes or in-line flow bodies support two sensors that are in contact with the gas. The sensors are resistance temperature detectors (RTDs). The Sage Metering sensors consist of highly stable reference-grade precision-matched platinum windings clad in a protective 316 SS or Hastelloy C sheath for industrial environments.
One of the sensors is heated by the circuitry and serves as the flow sensor, while a second RTD acts as a reference sensor and measures the gas temperature. The Sage proprietary sensor drive circuitry maintains a constant overheat between the flow sensor and the reference sensor. As gas flows by the heated sensor (flow sensor), molecules of the flowing gas transport heat away from this sensor, the sensor cools, and energy is lost. The circuit equilibrium is disturbed, and the temperature difference (ΔT) between the heated and reference sensors has changed. The circuit will restore the lost energy within one second by heating the flow sensor to fix the overheat temperature.
The electrical power required to maintain this overheat represents the mass flow signal. There is no need for external temperature or pressure devices.
An advantage of thermal flow meters is that they have no moving parts. This reduces maintenance and permits the use in demanding application areas, including saturated gas. They also do not require temperature or pressure corrections and provide excellent overall accuracy and repeatability over a wide range of flow rates. This meter style calculates mass flow rather than volume and is one of the few categories of meters that can measure flow in large pipes.
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