In certain applications, it is necessary to detect larger bubbles while ignoring smaller bubbles. If the desired bubble size is too large to ignore with a typical bubble sensor calibration, another way of accomplishing this is by utilizing two bubble sensors and logic gates. The smallest bubble size requiring detection must fill the entire inside diameter of the tubing to utilize this method. To determine whether a specific bubble size fills the inside diameter of a tube, the Bubble Size Calculator can be used. When a bubble fills the inside diameter of the tubing, it occupies a specific length. If the two bubble sensors are spaced along the tubing equivalent to the length of the smallest bubble requiring detection, both sensors will output an “Air” signal when a bubble equal to or larger than the specified bubble size is present. Any bubble smaller than this size will cause one or neither bubble sensor to output an “Air” signal. Please refer to the diagram below for an example where ignoring bubbles smaller than 500 microliters is desired.

Logic Gate Bubble Detection

*Note: Two smaller bubbles passing through the two sensors simultaneously may trigger a false positive. Further processing can be done on the
timing of the signals to account for these situations.