Guard ring for Capacitance sensor

Thread Starter


Joined Jun 24, 2011
Hi All
I would like to develop a capacitive sensor for diesel level for 6 inch depth. What I know are two types simple capacitive sensors
1- parallel plate and
2- cylinderical

I have found to use guard ring. I am not getting what is Guard ring and how it will be used in capacitive electrodes?

Please send me any good links or tutorials if you have for detailed design of capacitive electrodes.

Thanks in advance.


Joined Apr 24, 2011
I once worked on a capacitive level sensor of a cylindrical style. There was an inner solid cylinder enclosed within a hollow tube, the hollow tube had some extra holes to allow fluid to freely flow out. Together they formed a small capacitance which varied with the level of liquid within it, as the dielectric was changing.

The sensor was connected to a control box which would be in intimate electrical and mechanical contact with the liquid enclosure. The outer tube was intended to connect to earth ground, which was also the common ground of the sensor. The inner plate was connected thru two (for redundancy) large caps to isolate the circuit DC from the sensor and thus the interior liquid. (As a small cap in series with a much larger cap yields a net of the smaller cap value.)

I am unsure what the "guard" ring is, it is probably a third "plate" surrounding the inner two plates for either mechanical or electrical isolation. If you post a link to your reference I'll peek at what they may mean.