Capacitance sensing drop counter

A simple and inexpensive capacitive sensor which fits around any normal drip chamber has been devised. When it is made part of a suitable AC bridge circuit, the small changes in capacitance caused by the presence of a drop between the sensor plates can be reliably detected. The sensor is insensitive to its position on the drip chamber or to tilt of the chamber and unlike optical drop sensors, it is insensitive to ambient lighting.