Patent ID: 8875495

Claim:
A tank assembly comprising: a tank defining a chamber that is configured to store a selectively variable volume of liquid having an upper surface that is movable between a maximum level of liquid and a minimum level of liquid inside the chamber; a positive temperature coefficient heater disposed within the chamber and extending from the maximum level of liquid to the minimum level of liquid, wherein the amount of the heater disposed above the upper surface increases as the liquid is drawn out of the chamber; a source of electrical energy in selective electrical communication with the heater and configured to transfer electrical current to the heater; and a controller operatively connected to the heater and configured to monitor the amount of electrical current flowing to the heater; wherein the controller is configured to determine the volume of liquid in the chamber based on the amount of current being transferred to the heater; wherein the heater is comprised of a material; wherein the electrical resistance of the material varies with the temperature of the material; and wherein the material is characterized by a switching temperature above which the rate of increase of electrical resistance per unit of temperature rises.