PURPOSE: To enhance accuracy in the detection of suction air flow by distinguishing the forward air flow from the reverse air flow in a casing.
CONSTITUTION: A detection head 24 projecting into a casing 22 has first and second air channels 25, 26 formed symmetrically with respect to the axis O-O of the casing 22. The air channels 25, 26 are tapered in the opposite directions with respect to the directions of air flow (shown by arrows A and B). First and second heating resistors 28, 29 and temperature compensation resistors 33, 33 are disposed in the way of the air channels 25, 26. The air channel 25 is formed so that an upstream open end 25A has smaller diameter than a downstream open end 25B with respect to the forward air flow (shown by arrow A) whereas the air channel 26 is formed so that an upstream open end 26A has larger diameter than a downstream open end 26B with respect to the forward air flow (shown by arrow A).
TSUKADA MASAO
AOI HIROSHI
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