This is a question regarding the measurement of a fluid level (in my case water) using a capacitive sensor. Capacitive sensors are a common topic, but I have one specific question: It is necessary for both electrodes to be insulated from the fluid?
This is the basic concept that I am intending to implement: Capacitive Fluid Level Sensor (Instructables)
In that sensor design, both the inner and the outer electrodes are insulated from the fluid. (Note the remark that the sensor only worked correctly when the outer electrode was the ground pole.
I would like to implement a simplified design where the outer electrode is an aluminium tube, and the inner electrode is sealed inside in a PVC pipe. (obviously with an electrical connection though!)
Hence my question: Is it necessary to insulate the outer electrode? What effect will it have on the capacitance of the sensor if the dielectric medium (i.e. the water) is effectively connected to the outer electrode? Bear in mind that we are only trying to achieve a measurable change in capacitance.
The following topics here are of interest: