Patent ID: 7469601

Claim:
A flow meter using digital signals comprising: a tapered tube made of a substantially transparent or translucent material and mounted substantially perpendicularly and through which a fluid is made to flow; a float arranged in the tapered tube so that it is displaced in the vertical direction corresponding to a flow rate of the fluid; light emitting means for irradiating a ray to the tapered tube and the float to have it transmitted or reflected; entering means to which the transmitted or reflected ray is entered and reflected; first reflecting means in which the ray is entered from the entering means and reflected; second reflecting means provided opposite to the first reflecting means and reflecting the ray reflected from the first reflecting means toward the first reflecting means at least once and having the ray reflected by the first reflecting means several times; emitting means for having the ray reflected from the first reflecting means or the second reflecting means entered and emitting it; an image sensor into which the ray is entered from the emitting means and outputting an image of the float in the tapered tube; and a control portion for input-processing the image, detecting the position of the float in the tapered tube and outputting an electric signal indicating the flow rate; said flow meter further comprises at least one or more mask means having a hole portion being provided on the surface of the first reflecting means and/or the second reflecting means so as to narrow the ray to a light path only in a predetermined range.