Level detector for storage tanks for fluids

• US 20040200277A1
• Filed: 04/10/2003
• Published: 10/14/2004
• Est. Priority Date: 04/10/2003
• Status: Active Grant

• Current Assignee: Donald Edward Hewson, Joseph Rait, Robert S. Feldstein
• Original Assignee: Donald Edward Hewson, Joseph Rait, Robert S. Feldstein
• Inventors: Rait, Joseph, Hewson, Donald Edward, Feldstein, Robert S.
• Granted Patent: US 6,959,599 B2
• Time in Patent Office: Days
• US Class Current: 73/304R
• CPC Class Codes: G01F 23/246 thermal devices

Abstract

A level detector for storage tanks for fluids comprises a microprocessor, a network of resistive elements connected in series or parallel, and a plurality of conductive elements between them, connected across a power source. The resistive elements have a high temperature coefficient, and are heated by passing a high electric current through them, after which a low electric current is passed through them and the voltage between them is sampled by the microprocessor. The resistive elements lose heat through conduction, so that a pair of resistive elements can be detected having differential cooling between them as a consequence of being adjacent to the void within the tank or the fluid within the tank. Thus, an approximation of the fluid level within the storage tank can be determined and signalled remotely.

Claims

1. 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; and

wherein said microprocessor is further adapted to periodically measure the voltage at each of said conductive elements in said network and to store and analyse the voltage at each said conductive element over a period of time;

whereby after a series of measurements of the voltages of said conductive elements has been taken and analysed, while said resistive elements are giving up heat through conduction through 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.

2. The level detector of claim 1, wherein said network of resistive elements comprises said plurality of resistive elements connected in series.

3. The level detector of claim 1, wherein said network of resistive elements comprises said plurality of resistive elements connected in parallel.

4. The level detector of claim 1, wherein the resistance value of each of said plurality of resistive elements increases as a high electric current is passed through them.

5. The level detector of claim 1, wherein the resistance value of each of said plurality of resistive elements decreases as a high electric current is passed through them.

6. The level detector of claim 1, further comprising a signalling means for communicating data to a remote location;

whereby after an approximation of the fluid level within a storage tank has been made, data indicative of that approximation are sent to a remote location.

7. The level detector of claim 6, wherein said resistive elements are thermistors.

8. The level detector of claim 6, further comprising a substrate on which said resistive elements and said microprocessor are placed, whereby said substrate together with said power source and said remote signalling means may be adhered as a unitary entity to the wall of a storage tank.

9. The level detector of claim 8, wherein said resistive elements are areas of resistive ink applied to said substrate, and said conductive elements are areas of low resistivity material applied to said substrate.

10. The level detector of claim 1, wherein said power source is at least two batteries which are connected in series to provide said high voltage, together with switch means adapted to by-pass at least one of said at least two batteries to provide said low voltage from a remaining battery.

11. The level detector of claim 1, wherein said lower source is adapted to provide high power to said network of resistive elements during a heating cycle thereof, and to provide low power to said network of resistive elements during a measurement cycle thereof.

12. The level detector of claim 9, wherein said low resistivity material is copper.

13. The level detector of claim 6, wherein said microprocessor and said signalling means are further adapted to at least periodically test the voltage level of said power source and to send a signal to a remote location when said voltage level falls below a predetermined level.

14. The level detection of claim 8, wherein said substrate is polyaramide.