Hi, my RV has these sensors on the tank: https://www.recpro.com/rv-water-tank-adhesive-sensors/ They stick to the outside of the tank so they must be some kind of capacitance sensor.

Unfortunately the display board does not provide much precision, it has LEDs for Full, 2/3, 1/3, and Empty. I'd like to rig up a much more precise system, I assume I'll have to install a new sensor and display, but I am wondering what kind of signal comes out of these sensors? Maybe I could just tap into that? All 3 sensors connect to the display board using only two wires, which is interesting.

Occasionally on the display board I'll see one LED starting to light while the previous one starts to flicker. So maybe this is a linear signal that comes from these three sensors, and the control board interprets it as 1/3, 2/3, etc?

Thoughts on this these sensors work? I probably won't hurt the system by measuring voltage from each wire to ground, right?

 

I believe they are capacitive sensors, and it's likely that the wires are carrying an oscillating signal, so metering won't show much. An oscilloscope would be more informative.

You won't hurt anything by making voltage measurements across the wires.

 

Considering the type of sensors they are designed to replace, I'm certain they are a capacitive sensor that provides a digital signal when fluid is at its level.

So all that's possible to know is:

Less than ¼ tank

Between ¼ and ½ tank

Between ½ and ¾ tank

Greater than ¾ tank


"Analog" capacitive level sensors are available if you want better resolution. These can be a flexible tape or pcb adhered to the side of the tank running from top to bottom.

 

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Hi, my RV has these sensors on the tank: https://www.recpro.com/rv-water-tank-adhesive-sensors/ They stick to the outside of the tank so they must be some kind of capacitance sensor.

Unfortunately the display board does not provide much precision, it has LEDs for Full, 2/3, 1/3, and Empty. I'd like to rig up a much more precise system, I assume I'll have to install a new sensor and display, but I am wondering what kind of signal comes out of these sensors? Maybe I could just tap into that? All 3 sensors connect to the display board using only two wires, which is interesting.

Occasionally on the display board I'll see one LED starting to light while the previous one starts to flicker. So maybe this is a linear signal that comes from these three sensors, and the control board interprets it as 1/3, 2/3, etc?

Thoughts on this these sensors work? I probably won't hurt the system by measuring voltage from each wire to ground, right?
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Here is a review that may help: