LMM-H03

LMM-H03 is a thermodynamic sensing element for the bidirectional
measurement of mass air flow in a well defined channel. It is dedicated for
applications with high reliability requirements such as medical or industrial
gas flow applications. Mounted directly within the flowing media the LMMH03
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-H03 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-H03 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.