| 摘要 |
PURPOSE:To prevent the detection of an abnormality of a flow rate even when a float fluctuates a little in the vicinity of the center of a set flow rate, by detecting the abnormality of the flow rate only when the float moves beyond a prescribed range between an optical sensor for the upper limit and a sensor for the lower limit. CONSTITUTION:A flow rate is determined to be normal when a float 2 of a flowmeter 3 is located within a prescribed range (w) between optical sensors 17a, 19a for the upper limit which detect the upper limit of a set flow rate and optical sensors 17b, 19b for the lower limit which detect the lower limit of said flow rate. Only when the float 2 moves up and down beyond the range (w), an abnormality of the flow rate can be detected by the optical sensors 17a, 19a for the upper limit or the optical sensors 17b, 19b for the lower limit. Even when the float 2 fluctuates a little in the vicinity of the center of the set flow rate accordingly, the abnormality of the flow rate is not detected, and thus the detection of the flow rate can be stabilized.
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