سنسور و مبدل سنسور جریان سیال (فلو)

Product Attributes

Introduction

The AWM40000 Series airflow sensors are based on proven microbridge technology, available in both unamplified sensor-only devices and amplified signal-conditioned devices. The microbridge mass airflow sensor operates on the principle of heat transfer. Mass airflow is directed across the surface of the sensing element. The output voltage varies proportionally to the mass of air or other gas flowing through the inlet and outlet of the package. The sensor features a unique silicon die based on advanced microstructure technology. It consists of a thin-film thermally isolated bridge structure containing a heater and temperature-sensing elements. The bridge structure provides sensitive and fast response to air or other gas flow across the die. Dual sensing elements located on either side of the central heating element indicate both flow direction and flow rate. A specially designed housing precisely guides and controls airflow through the microstructure sensing element. The mechanical design of the package allows easy mounting onto a PCB. Laser-trimmed thick-film and thin-film resistors ensure consistency and interchangeability between devices. The microbridge mass airflow sensors use temperature-sensitive resistors deposited within silicon nitride thin films. These are suspended in bridge form over silicon-etched cavities. The die is located in a precisely dimensioned airflow channel to provide repeatable flow response. Efficient thermal isolation of the heater and sensing resistors is achieved by etching a cavity beneath the flow sensor bridge. The small size and thermal isolation characteristics of the microbridge mass airflow sensor provide extremely fast response and high sensitivity to flow. Dual Wheatstone bridges govern airflow measurement — one for closed-loop heater control and the other containing dual sensing elements. The heater circuit minimizes drift due to ambient temperature variations by providing an output proportional to mass flow. The circuit maintains the heater temperature at a constant differential of 160°C above the ambient air temperature, which is sensed by an on-chip heat-sink resistor. The proportional voltage output of the device corresponds to the differential voltage across the Wheatstone bridge circuit. The unamplified version requires a heater control circuit (Figure 2) and a sense bridge supply circuit (Figure 3) to operate per specification. These two circuits are not on the sensor board and must be provided in the application. A differential amplifier circuit (Figure 4) can be used to provide output gain and/or introduce a voltage offset to the sensor output (Figure 5). The amplified version can be used to increase output gain and introduce a voltage offset. The circuits shown in Figures 2, 3, and 4 are all integrated on-board.

Features

• Precision silicon micromachining
• Sensitive to low flow rates (0.1 SCCM to 6 SLPM)
• Suitable for higher flow rates
• Low power consumption for portable and battery-powered applications
• Analog output
• Standard 2.54 mm [0.10 in] mounting centers
• Laser-trimmed interchangeability
• Accurate low-pressure detection

Applications

• Respirators and ventilators
• Oxygen concentrators and oxygen conservers
• Anesthesia machines
• HVAC damper control
• Gas analyzers