A laminar flow element in the main channel generates a slight pressure drop, which drives a small proportion of the full flow through the bypass channel. The sensor located therein records the mass flow rate directly by measuring the temperature differential. The measurement in this case is taken in a specially shaped flow channel whose walls contain a Si chip in one place with an exposed diaphragm. Using CMOSens ® technology, a heating resistor is connected to this diaphragm along with two temperature sensors upstream and downstream of it. If the heating resistor is supplied with a constant voltage, the voltage differential of the temperature sensors is a measure of the mass flow of the gas flowing through the flow channel past the chip.
Function diagram of the bypass sensor in CMOSSens - technology (cross section from the bypass channel)