Airflow Sensors
Microbridge Mass Airflow
AWM Series
AWM 1000/2000/3000 Series
1 State-of-the-art silicon
1 Sensitive to low flows – 0.1 sccm to
1 Adaptable for use with higher flows
(See Application Note 2 page 128.)
1 Fast response time
1 Analog output
1 Low power consumption
The microbridge mass airflow sensor operates on the theory of heat transfer. Mass
airflow is directed across the surface of
the sensing elements. Output voltage varies in proportion to the mass air or other
gas flow through the inlet and outlet ports
of the package. The specially designed
housing precisely directs and controls
the airflow across the microstructure
sense element. Mechanical design of the
package allows it to be easily mounted to
printed circuit boards.
The microbridge mass airflow 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 elements. The bridge structure provides a sensitive and fast response to the flow of air or other gas over
the chip. Dual sensing elements positioned on both sides of a central heating
element indicate flow direction as well as
flow rate. Laser trimmed thick film and thin
film resistors provide consistent interchangeability from one device to the next.
AWM 40000 Series
Repeatable response
Laser-trimmed interchangeability
Accurate, cost effective flow sensing
In-line printed circuit board terminals
Standard 0.100N (2,54mm) mounting
1 Accurate sensing of low pressure
0.001N to 4.0N H2O (.003 to 10mBar)
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, shown below. 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 elements. 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.
AWM 5000 Series
1 Damper control for heating, ventilation,
and air conditioning systems
1 Gas analyzers
1 Low vacuum control
1 Process control
1 Medical respirators and ventilators
1 Oxygen concentrators
1 Leak detection equipment
1 Vent hoods
1 Anesthesia control
1 Gas metering
1 Gas chromatography
Dust contamination may be possible in
some applications, the effects of which
can be minimized. By design, dust particles that may be present in the air
stream will flow past the chip parallel to
the chip surface. In addition, the microstructure chip produces a thermophoretic effect, which repels micrometer-sized
dust particles away from the bridge
Dust adherence to chip edges and
channel surfaces can be prevented using a simple filter. A disposable fivemicron filter used in series on the upstream side of the airflow device will
provide adequate filtering in most applications. For a list of possible filter sources, see Filter Manufacturers, page 126.
AWM Series Microbridge Mass Airflow
Sensors are NOT designed to sense
liquid flow and will be damaged by liquid
flow through the sensor.
Honeywell 1 MICRO SWITCH Sensing and Control 1 1-800-537-6945 USA 1 F1-815-235-6847 International 1 1-800-737-3360 Canada