Electronic – Using enameled copper wire as a capacitor for measuring water level in a tank

capacitorfrequencymicrocontrollersensor

I'm trying to make a capacitive water level sensor using two enameled copper wires used in transformers. I've used sanitary silicone to insulate the bottoms of the wires. (Coating is insulated by default.) The distance between them is 0.5 cm, they are submerged in a water tank made out of acrylic glass. As the fluid level rises, capacitance should change, the "sensor" is connected to a IC555 timer which is used to generate a square wave with frequency inversely proportional to the capacitance.

Then I'm calculating the time which passes between two rising edges of the pulse using an STM32 microcontroller. I've connected the IC555 timer output to an oscilloscope and when the tank is empty it gives a square wave of a certain frequency, but when the water level rises nothing changes. What did I do wrong? What could be the issue? I'd like to hear someone more experienced on the matter since I'm just a student and I lack experience. Any help would be appreciated, thanks in advance.

Best Answer

Unfortunately no. Several other good answers address the capacitance problem. Another problem is that the lacquer on enamelled copper wire is not guaranteed pinhole free i.e. the insulation is likely not perfect. In winding a transformer or inductor this doesn't matter, since the pinholes are unlikely to coincide and cause a shorted turn. Varnish impregnation after winding also helps to stop corrosion by moisture getting in the pinholes.

In your application, if there is even one pinhole in each wire, and the water conducts any of the signal, this is likely to swamp any capacitive effect.