Patent ID: 8601866

Claim:
A sensing device for sensing whether an electrically-conductive fluid has reached a predetermined level within a container, said sensing device comprising: a first electrode that is electrically connected to a source of alternating positive and negative pulses; a second electrode that is electrically connected to ground; a gap between the first electrode and the second electrode, this gap being filled with the fluid when it reaches the predetermined level in the container, but not when the fluid is below this predetermined level; circuitry causing current flow from the first electrode to the second electrode when gap is filled with the fluid and the first electrode is receiving one of a positive voltage pulse or a negative voltage pulse from the source, and causing current flow from the second electrode to the first electrode when the gap is filled with the fluid and the first electrode is receiving the other of a positive voltage pulse or a negative voltage pulse from the source; wherein the circuitry comprises: a capacitor (C 2 ) that charges during positive voltage pulses and a resistor (R 6 ) that ensures that the capacitor (C 2 ) discharges when the gap is not filled with fluid; and a diode (D 1 ) that insures that the capacitor (C 2 ) does not drain during negative voltage pulses.