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What is a Thermal Mass Flow Meter?

• What is a Thermal Mass Flow Meter? It is a meter that directly measures the gas mass flow based on the conductive and convective heat transfer principle.
• All Meters have probes (Insertion Style) or Flow Bodies (In-Line Style) that support a pair of sensors in contact with the gas.
• The sensors are RTDs, which are resistance temperature detectors. They consist of highly stable reference-grade platinum windings. In fact, we use the same material that is used as Platinum Resistance Standards at the NIST.
• The RTDs are clad in a protective 316 SS sheath for industrial environments.
• One RTD [See Diagram below] is self-heated by the circuitry and serves as the flow sensor. The other RTD acts as a reference sensor and measures the gas temperature. Essentially it is used for temperature compensation.
• 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), the molecules of flowing gas carry heat away from this sensor, and the sensor cools down as it loses energy. The circuit equilibrium is disturbed, and momentarily the temperature difference between the heated sensor and the reference sensor has changed. The circuit will automatically (within 1 second) replace this lost energy by heating the flow sensor, so the overheat temperature is restored.
• The current required to maintain this overheat represents the mass flow signal. There is no need for external temperature or pressure devices.