This paper reports the effect of the operation mode of a thermal micro flow sensor on the response characteristics. Micro Flow Sensor (MFS) is a thermal type fluid mass flow sensor fabricated by utilizing the MEMS technology. The performance of MFS greatly depends on the operation mode. The constant temperature mode provides wider measuring range and faster dynamic characteristics than the others. In the constant temperature mode, it is typically classified into two types of the control circuit, individual or integrated mode. The purpose of the present study is to clarify the effect of the operation mode on static and dynamic characteristics of MFS. Two arrangements of MFS with the different distance between the heaters are tested. In the static characteristic test, the output signal level of the individual mode is much larger than that of the integrated mode. It depends on the distance between the heaters. The dynamic characteristics are evaluated in the frequency range up to 500 Hz under the oscillating flow condition generated by an acoustic speaker in an air flow channel. As a result, the individual mode indicates faster response than the integrated mode, and it is found that the frequency response of the individual mode depends on the distance between the heaters.

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