This invention relates to sensing the presence of bubbles in a liquid, and a particular application thereof is the detection of air bubbles in serum or blood during infusion thereof into a patient. In such procedures it is important to insure that gas be prevented from being infused with the liquid, since air emboli can be extremely dangerous in a patient. To prevent gas from being infused it has become common practice to locate a bubble detector downline of the metering apparatus pump to automatically stop the apparatus should gas bubbles be detected.
Various instruments have been developed for preventing air bubbles from being infused into a patient along with a liquid, typical of which are those disclosed in U.S. Pat. Nos. 4,366,384, 4,312,341, 2,835,252, and 4,367,736. Such prior instrumentation commonly suffers from unreliable operation because of low signal level, electronic drift, and/or difficult mechanical alignment.