How Does Thermal Flow Measurement Work?

The MMS50X and MMS65X series sensors utilize MEMS thermal technology for flow measurement. At the heart of the sensor is a thermal flow chip containing a heater sandwiched by two equally spaced thermopiles. With the absence of gas flow, the thermopiles absorb roughly the same amount of heat and the temperature difference between the two thermopiles is negligible. As gas flow increases, convection forces the downstream thermopile to receive more heat and a difference in temperature between the upstream and downstream thermopiles can be correlated to flow velocity or volumetric flow rate.