A High Performance MEMS Flow Sensor Based on a New Sensing Method

Abstract

This paper presents a new type of bidirectional thermal flow sensor which has a wide dynamic range and excellent temperature characteristics. This sensor has a pair of heaters and a temperature sensor on a diaphragm. The heaters are located on opposite sides to each other. A single bridge circuit provides an adequate heating current to the upper stream heater so as to keep the voltages supplied to each heater balanced. The heating current, which represents the required sensor output, increases as the flow rate increases. A reverse flow can be also detected since the current decreases when the flow is reversed. A wide dynamic range of 500 and excellent temperature characteristics of less than ±3% of the reading value of flow rate (from 0 to 50°C) were obtained. This sensor responded to a step change of flow rate from 40 to 137 L/min within 0.5 sec.