LMM-H04型氣體流量傳感器

LMM-H04.pdf

LMM-H04 is a thermodynamic sensing element for the unidirectional measurement of mass air flow in a well
defined channel. It is intended for applications with high reliability requirements such as automotive, medical or
industrial gas flow applications. Mounted directly within the flowing media the LMM-H04 is sensitive against the
heat transfer on a micrometer scale. This heat transfer is detected by a micro-machined silicon device which is
mounted on ceramic substrate defining the geometry of the sensing element.

The functional principle of the LMM-H04 is a hot film anemometer, which is the thin film version of the hot wire
anemometer. A thin film heating element (heater) is heated to a defined temperature difference with respect to
the air. At zero flow there is heat dissipation due to the thermal conductivity of the air. With applied flow the heat
dissipation increases steadily with the flow rate.

The sensing element can be operated at Constant Power and Constant Voltage mode. However, it is
recommended to operate LMM-H04 in the described Constant Temperature Difference (CTD) mode. In the CTD
mode the electronics detects any change of the thermal equilibrium very quickly and compensates it by
adjusting the power settings through the heaters. This allows a very reliable mass flow measurement with a very
short time constant which is in the order of milliseconds.