Patent ID: 6959599

Claim:
A level detector for storage tanks for fluids, comprising: a power source, a microprocessor, a plurality of resistive elements connected in a network across said power source, and a plurality of conductive elements joining said resistive elements in said network; wherein, in use, said plurality of resistive elements are attached to the side wall of a storage tank over the height thereof where the level of fluid within the storage tank is expected to vary over time, so that at least the approximate level of fluid in the storage tank may be detected from time to time; wherein said resistive elements have a high temperature coefficient whereby when a high electric current is passed through them their resistance changes significantly from a first resistive value towards a second resistive value, and they become heated; and when a low electric current is passed through them after they are heated their resistance returns from their second resistance value towards their first resistive value, and their heat is given up through heat conduction; wherein said power source is adapted to provide a high voltage and a low voltage across said network of resistive elements; wherein the spacing between adjacent pairs of said resistive elements is greater than the thickness of the wall of the storage tank to which said resistive elements are attached; wherein said microprocessor is adapted to control said power source to switch from said high voltage operation to said low voltage operation after a predetermined heating period; wherein said microprocessor is further adapted to periodically measure the voltage at each of said conductive elements in said network and to store and analyze the voltage at each said conductive element over a period of time; and wherein the resistance value of each of said plurality of resistive elements decreases as a high electric current is passed through them, whereby after a series of measurements of the voltages of said conductive elements has been taken and analyzed, while said resistive elements are giving up heat through conduction though the wall of the storage tank to which they are attached, an adjacent pair of resistive elements can be identified wherein the resistance of the lower resistive element of said pair is decreasing at a greater rate than the resistance of the upper resistive element of said pair due to increased heat conductance away from said lower resistive element, so as to provide an approximation of the fluid level within said storage tank.