PURPOSE: To eliminate the influence caused by the absorption of light in fluid flowing in a transparent tube 12, on the maximum detection signal of air bubble flowing therein.
CONSTITUTION: Light is radially directed while it passes through a transparent tube 12 in the orthogonal direction to the longitudinal axis of the tube 12 and the light extends to the inside of a specified region 14 when the tube 12 is filled with liquid while extends over the region when the tube 12 is filled with gas. By receiving only the light extending over the region after passing through the tube 12, the light is received at the opposite position to the position to which the light is directed. The output signal 19 indicating the existence of liquid or gas in the tube 12 is generated in response to the quantity of light received.
MARUUN TOUUMA
JIYOOJI II ZUABETAKISU
