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Internal Structure and Detection Principle of Flow Sensor

MEMS sensors are micro-electromechanical systems (Micro-electroMechanicalSystems), which is a new type of sensor manufactured using microelectronics and micromachining technology. Compared with traditional sensors, it has the characteristics of small size, low cost, low power consumption, high reliability, and easy integration. Avcray’s MEMS flow sensor uses its unique high-precision processing technology to encapsulate the core components of the flow sensor in a MEMS chip with a size of only 1.5*1.55*0.4mm. This ultra-fine MEMS sensor can not only detect changes in gas flow rate of 1 mm/sec, but also achieve high-precision mass production.

Internal structure of flow sensor

This sensor chip adopts a mass flow detection method using a hot wire. There is a heater in the center of the chip. The upstream thermopile (A) and the downstream thermopile (B) are arranged on both sides of the heater, and a base temperature measuring body is arranged near the thermopile. They are all manufactured by semiconductor technology. . The heater and the bottom of the thermopile array form a cavity, so that the thermopile can efficiently detect the heat of the heater.

Detection principle of flow sensor

By adding a constant current to the MEMS chip, the heater in the center of the chip generates heat. When there is no wind, the thermopile upstream of the heater and the thermopile downstream of the heater are thermally balanced, and the corresponding thermoelectromotive voltages of the two are equal, that is, Vu=Vd. When there is gas flowing, the heat source moves downstream along the direction of the gas flow. At this time, the electromotive force of the downstream thermopile becomes larger, that is, Vd>Vu. The output difference of the two thermopiles is roughly proportional to the square root of the gas mass flow through the sensor surface. The output sensitivity and mass flow rate depend on the composition ratio of the gas. Tiny signals can be amplified by an amplifier circuit, and then the gas flow can be detected electronically. The adjusted output voltage of the air volume sensor is equivalent to the flow velocity when the mass flow is 25°C and 101.3kPa.

Application of flow sensor

Blockage detection—projector, PC, server

Combustion control—fuel cell, water heater, boiler

Air volume detection—pipe, airflow measurement, air conditioning

Feeding rate control—anesthesia apparatus, oxygen generator

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