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2032 |
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Development of a Thermal Type Micro Flow Sensor for Pulsating Flow Measurement |
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Equipment, Machines & Instruments: MEMS, LIGA & Nanotechnology |
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Development of a Thermal Type Micro Flow Sensor for Pulsating Flow Measurement
Koichi Igarashi, Kenji Kawashima, Toshiharu Kagawa
Tokyo Institute of Technology
4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503. Japan,
Recently, there are demands for the development of flow sensor with quick response and high sensitivity to realize unsteady gas flow measurement in various fields like semiconductor manufacturing, fuel cells and artificial ventilators. Therefore, many researchers have developed micro sized thermal type flow sensor using micromachining technologies [1]. Most of traditional micro thermal flow sensors have introduced constant-power method that is to keep the supplying electric power to heater and obtain the flow rate by measuring the temperature distribution. However, dynamic characteristics of these traditional sensors are examined just from the response at transient flow rate change. Therefore, we have developed a new thermal type micro flow sensor which is introduced constant-temperature method. This sensor achieved quick response to sinusoidal flow rate change up to 5 Hz [2].
However, its electric power consumption was not reduced enough. And also, frequency characteristic of the sensor was not enough to use high speed flow rate control. Therefore, the purpose of this research is to redesign the driving circuit of the sensor to reduce the power consumption and improve the sensor characteristic.
We have developed and fabricated a new thermal type micro flow sensor measured 3 times 3 mm square. The driving electric circuit works to keep the temperature deference between the heater and the working gas constant, and we can obtain the flow rate by measuring the electric power consumption of this circuit. This sensor has a simpler structure compared with traditional one because of the driving method. To fabricate this sensor, we used micromachining technologies.
The electric power consumption depends on the electric characteristic of the hot wire. So, we designed the shape of the hot wire to achieve the ideal driving condition and redesigned a driving electric circuit. As a result, the electric power consumption was reduced more than 50% even the resolution of the sensor remained almost the same as compared with the former one at the steady flow. Therefore, it was showed that the circuitry method which we have proposed is effective in power-saving.
Additionally, we have measured pulsating flow rate change using the newly developed sensor. Because the quantity of direct measurements depends upon the flow velocity, the sensor should be positioned in a location with a known flow rate. Therefore, we designed the flow channel and the sensor position to decrease the difference between the steady and unsteady velocity profiles. We also considered the velocity profile theoretically and confirmed experimentally that the sensor follows up to 10Hz of sinusoidal flow.
This sensor is expected to use for a semiconductor manufacturing process, gas flow rate management of a fuel cell, and minute leak land survey system.
[1] N. T. Neguyen, Micromachined flow sensors - a review, Flow Meas. Instrum. , 8-1, pp. 7–16 (1997).
[2] K. Igarashi et al, Effect of sensor structure on constant-temperature type micro flow sensor characteristics, SICE Annual Conference, CD-ROM (2004).
Keywords:MEMS, flow sensor, pulsating flow measurement |
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