Point Capacitance Biological filter detector
![](https://www.hawker-electronics.co.uk/images/capap4_resized.gif)
The tip of the capacitance probe will detect the metal arm of the biological filter as it rotates.
To improve the system you can mount a metal plate on the end of the arm.
As the filetr rotates the probe will detect the metal probe as it passes by.
A simple but effective system
The probe can be a low powered stand alone probe or a probe with a separate controller incorporating time delays