With mutual capacitance sensors, moisture droplets on an isolated sensor node will not cause accidental touch detection. The sensor will show a negative touch delta, often denoted an ‘anti touch’, as the droplets increase the X-Y coupling – via the capacitance formed between the water and the X line, Cwx, and the one between the water and the Y line, Cwy, – but do not provide a significant ground return path.
In many designs, the sensor is one of a group of sensors near each other and shares the PCB with many components and signals. In this case, a water droplet that crosses from the sensor node over to any other circuit component and forming a capacitive coupling to both will cause an increase in ground return coupling. In this case, the net result may be towards touch delta and false touch detection.
