What is a thermal mass flow meter?
Flow measurement is the measurement of the amount of flow. A thermal mass flow meter is a device that measures gas mass flow based on the principle of heat transfer.
These precision flow meters are widely used in various industries with a wide range of different applications. These applications are grouped into energy saving, environmental impact functions, industrial use and measurement with the specific gas specified.
How does a thermal mass flow meter work?
The thermal mass flow meter measures gas flow based on the principle of convective heat transfer. The probes are two sensors in contact with the gas. The sensors are resistance temperature detectors (RTDs). Sage measurement sensors consist of highly stable, sensitive and platinum windings covered with a protective 316 SS or Hastelloy C sheath for industrial environments.
One of the sensors is heated by the circuit and acts as a flow sensor, while a second RTD acts as a reference sensor and measures the gas temperature. The sensor circuit maintains the temperature difference between the flow sensor and the reference sensor. As gas flows through the heated sensor (flow sensor), the molecules of the flowing gas remove heat from this sensor, the sensor cools down and energy is lost. The circuit is out of balance and the temperature difference (ΔT) between the heated and reference sensors changes. The circuit restores the lost energy within one second by heating the flow sensor to correct the temperature difference. The electrical power required to maintain this temperature difference is directly proportional to the mass flow value. No external temperature or pressure transmitter is required for compensation. Mass flow is measured directly. In case of volumetric flow, since the temperature of the fluid is measured directly, the density value is also calculated directly by the electronic unit. Then the volumetric flow is calculated clearly with the mass, volume, density formulation. For volumetric flow, it can be measured directly in Nm3/h and there is no need to make extra pressure and temperature compensation for volumetric flow.
An advantage of thermal flowmeters is that they have no moving parts. They also do not require temperature or pressure compensation and provide excellent accuracy and repeatability over a wide range of flow rates. They offer the advantage of high measurement accuracy in large diameter lines and the ability to measure low flows thanks to a high turn down ratio..
