The OPB350 Liquid Sensor Series is designed to work with 1/16” [1.6mm], 1/8”[3.2mm], 3/16” [4.8mm], and 1/4” [6.3mm] outside diameter clear tubes. Multiple output states such as “fluid present”, “no fluid present”, and “no tube present” can be recognized. Clear liquid causes the phototransistor to sink the maximum current, while a dark liquid causes it to sink the least current. As bubbles pass through the tube, the signal will vary between the “liquid present” and “no liquid” states. If no tube is present, the phototransistor sinks current between the dark fluid and clear fluid states. The designer must identify the typical current values for each situation and design the output reference circuitry to match.