MEMS sensor, or Micro-electro Mechanical Systems, is a new type of sensor manufactured by 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. Omron MEMS flow sensor, using its original high-precision processing technology, encapsulates the core device 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/s, but also enable mass production with high precision.

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 thermopile (A) on the upstream side and the thermopile (B) on the downstream side are arranged on both sides of the heater, and a base temperature measuring body is arranged near the thermopile, which are all manufactured by semiconductor technology. . A cavity is formed at the bottom of the heater and the thermopile array, so that the thermopile can efficiently detect the heat of the heater.

Detection principle of flow sensor

By applying a constant current to the MEMS chip, the heater in the center of the chip generates heat. When there is no wind passing through, the thermoelectric voltages corresponding to the upstream thermopile and downstream thermopile of the heater are equal due to the thermal balance, that is, Vu=Vd. When there is gas flow, the heat source moves downstream with the direction of the gas flow, and the electromotive force of the downstream thermopile becomes larger at this time, that is, Vd > Vu. The difference in the outputs of the two thermopiles is roughly proportional to the square root of the gas mass flow across the sensor surface. The output sensitivity and mass flow depend on the gas composition ratio. The tiny signal can be amplified by an amplifier circuit, and then the gas flow is detected electronically. The adjusted output voltage of the air flow sensor is equivalent to the flow rate at 25°C and 101.3kPa mass flow rate.

Application of flow sensor

Blockage Detection—Projector, PC, Server

Combustion control—fuel cells, water heaters, boilers

Air volume detection — ducts, airflow measurement, air conditioning

Feeding rate control—anesthesia machine, oxygen generator

Omron D6F series flow sensor types

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