The AWM40000 Series Airflow Sensors are based on proven microbridge technology and include both unamplified sensor-only devices and amplified signal conditioned devices.The microbridge mass airflow sensor operates on the th-eory of heat transfer. Mass airflow is directed across the surface of the sensing ele-ments. Output voltage varies in proportion to the mass air or other gas flow through the inlet and outlet ports of the package.This sensor has a unique silicon chip based on advanced microstructure technology. It consists of a thin film, thermally-isolated bridge structure containing heater, and temperature sensing ele-ments. The bridge structure provides a sensitive and fast response to the flow of air or other gas over the chip. Dual sensing ele-ments positioned on both sides of a central heating ele-ment indicate flow direction as well as flow rate.The specially-designed housing precisely directs and controls the airflow across the microstructure sensing ele-ment. Mechanical design of the package allows it to be easily mounted to printed circuit boards.Laser-trimmed, thick film and thin film resistors provide consistent interchangeability from one device to the next. The microbridge mass airflow sensor uses temperature sensitive resistors deposited within a thin film of silicon nitride. They are suspended in the form of two bridges over an etched cavity in the silicon. The chip is located in a precisely dimensioned airflow channel to provide a repeatable flow response. Highly effective, thermal isolation for the heater and sensing resistors is attained by etching the cavity space beneath the flow sensor bridges.
The small size and thermal isolation of the microbridge mass airflow sensor are responsible for the extremely fast response and high sensitivity to flows. Dual Wheatstone bridges control airflow measurement–one provides closed loop heater control, the other contains the dual sensing ele-ments.The heater circuit minimizes shift due to ambient temperature changes by providing an output proportional to mass flow. The circuit keeps the heater temperature at a constant differential (160°C) above ambient air temperature which is sensed by a heat-sunk resistor on the chip. The ratiometric voltage output of the device corresponds to the differential voltage across the Wheatstone bridge circuit.The unamplified versions require both the heater control circuit (Fig. 2) and the sensing bridge supply circuit (Fig. 3) for operation per specification. These two circuits are not on board the sensor and must be supplied in the application. The differential amplifier circuitry (Fig. 4) may be useful in providing output gain and/or introducing voltage offsets to the sensor output (Fig. 5).The amplified versions can be used to increase output gain and introduce voltage offsets. The circuits shown in Figs. 2, 3, and 4 are all provided onboard.
FEATURES
• Precision silicon micromachining
• Sensitivity to low flows (0.1 SCCM to 6 SLPM)
• Adaptable for use with higher flows
• Low power consumption allows for use in portable devices and battery-powered applications
• Analog output
• Standard 2,54 mm [0.10 in] mounting centers
• Laser-trimmed interchangeability
• Accurate sensing of low pressure
Datasheet Download
