The micro-bridge air flowmeter works using the principle of heat transfer. The air mass is routed over the surface of the measuring elements. The output voltage varies in proportion to the air mass or the flow of other gases through the inlet and outlet ports of the package. The specially designed enclosure routes and guides the air flow over the micro-structure sensor element. The mechanical design of the package allows easy mounting on circuit boards.
The micro-bridge air flowmeter has a unique silicon chip with a highly developed micro-structure technology. It features a thermally insulated thin-film bridge structure consisting of a heater and temperature measuring elements. The bridge structure provides sensitive and rapid response to air flows and other flows on the chip. Dual measuring elements located on both sides of a central heating element indicate the flow direction as well as the flow rate. Laser-matched thick-film and thin-film resistors enable consistent interchangeability from one device to the next.
The micro-bridge air flowmeter has temperature-sensitive resistors positioned in a thin layer of silicon nitride. They are positioned in the form of two bridges over an etched cavity in the silicon. The chip is located in a precisely dimensioned air flow channel, which enables a repeatable air flow response. Highly efficient thermal insulation for the heating and sensor resistors is achieved by etching the cavity under the air flow measuring bridges. The small size and thermal insulation of the micro-bridge air flow meter enables extremely fast response and high sensitivity to flows.
Two Wheatstone bridges control the air flow measurement – one provides closed-circuit heating control and the other contains double sensor elements. The heating control circuit minimises switching operations caused by changes in the ambient temperature as one output is proportional to the mass flow. The heating circuit keeps the heating temperature (160°C) constantly above the ambient temperature, which is detected by a thermal resistor on the chip. The ratiometric output voltage of the unit corresponds to the differential voltage in the Wheatstone bridge circuit.
Micro-bridge air flow meters from the AWM series are not designed to detect liquid flows, and will be damaged by liquid flowing through the sensor.
• Precise silicon micro-machining
• Sensitive to low air flows – 0.1 sccm to 20 SLPM
• Adjustable for use with greater air flows
• Fast response time
• Analogic output
• Low power consumption
• Repeatable response
• Laser trimmed interchangeability
• Accurate, cost-effective air flow detection
• Inline PCB connectors
• Standard mounting centre points 2.54 mm (0.100 inch)
• Exact measurement of low pressure 0.001 - 4.0 inches H2O (0.003 to 10 mbar)
Technical data:
Signal conditioning: Amplified
Flow/pressure range: +1000 sccm (1.0 SLPM)
