ABSTRACT
The point measurement of velocity of gaseous fluids has been made for some time with hot wire anemometer type sensors. Sensitivity of certain micro-sensors to gaseous fluid parameters might form a basis for the measurement of energy flow under advantageous conditions of automatic compensation for pressure and temperature changes. The sensor measures mass flow quite accurately under density changes caused by variations in ambient temperature and ambient pressure. The sensor circuit is a conventional Wheatstone bridge circuit. The error integrator is the active component in the heater circuit. It integrates the voltage differences seen on the Wheatstone bridge, and changes the voltage to the heater to maintain the bridge circuit balance. The resulting temperature and corresponding resistance differential yields a circuit output measurement of the flow rate. Standard silicon was chosen for the substrate because of its desirable anisotroplc etching properties and its suitability for later circuit integration with the transducer.
