Method and apparatus for monitoring the voltage of a battery

• US 20060267554A1
• Filed: 05/27/2005
• Published: 11/30/2006
• Est. Priority Date: 05/27/2005
• Status: Active Grant

• Current Assignee: Savi Technology Incorporated
• Original Assignee: Savi Technology Incorporated
• Inventors: Chan, Joseph S., Cargonja, Nikola, Ahn, Don H.
• Granted Patent: US 8,164,307 B2
• Time in Patent Office: Days
• US Class Current: 320/130
• CPC Class Codes: G01R 31/2822 of microwave or radiofrequency circuits of attenuation, gain, e.g. using network analyzers G01R27/28
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/3835 involving only voltage measurements

Abstract

One aspect of the invention involves: monitoring a voltage of a battery over time; evaluating whether a rate of voltage decrease of the battery is in excess of a threshold; and indicating that the battery is subject to a low voltage condition when the rate of voltage decrease exceeds the threshold. Another aspect of the invention involves: causing a circuit powered by a battery to respond to battery replacement by thereafter applying a selected load to the battery during a selected time interval. A further aspect involves: periodically sampling a voltage of a battery; and applying a load to the battery during a selected time interval before each sampling of the battery voltage.

Claims

1. A method comprising:

monitoring a voltage of a battery over time;

evaluating whether a rate of voltage decrease of said battery is in excess of a threshold; and

indicating that said battery is subject to a low voltage condition when said rate of voltage decrease exceeds said threshold.

2. A method according to claim 1, wherein said monitoring of said voltage over time includes:

monitoring an ambient temperature; and

normalizing measured voltage values as a function of the ambient temperature.

3. A method according to claim 1, wherein said monitoring includes:

tracking the drain of charge from said battery;

determining a series of points in time for which a substantially equal amount of charge is drained from said battery between each pair of successive said points in time;

sampling said voltage of said battery at each of said points in time;

calculating the difference between said voltage samples from successive said points in time; and

comparing said calculated difference to said threshold.

4. A method according to claim 3, including applying a load to said battery for a selected time interval before each said sampling of said voltage of said battery.

5. A method according to claim 1, including providing a radio frequency identification tag that includes and is powered by said battery, said tag having an antenna, and having a circuit that includes a transmitter coupled to said antenna, said circuit transmitting through said transmitter and said antenna a radio frequency signal that indicates whether a determination has been made that said battery is subject to a low battery condition.

6. A method according to claim 1, including selecting a lithium cell to serve as said battery.

7. A method comprising:

causing a circuit powered by a battery to respond to battery replacement by thereafter applying a selected load to said battery during a selected time interval.

8. A method according to claim 7,

including configuring said selected time interval to have a plurality of alternating first and second time intervals;

and

wherein said applying of said selected load includes applying said load to said battery during each of said first time intervals and removing said load from said battery during each of said second time intervals.

9. A method according to claim 8, including:

selecting said first time intervals to each be about 25 ms;

selecting said second time intervals to each be about 25 ms; and

selecting said selected time interval to be about 2 seconds.

10. A method according to claim 7, including sampling a voltage of said battery at a point in time after said applying of said selected load.

11. A method according to claim 7, including selecting a lithium cell to serve as said battery.

12. An apparatus comprising:

a battery; and

a circuit that is powered by said battery and that responds to battery replacement by thereafter applying a selected load to said battery during a selected time interval.

13. A apparatus according to claim 12,

wherein said selected time interval includes a plurality of alternating first and second time intervals;

and

wherein said circuit applies said selected load to said battery during each of said first time intervals and removes said load from said battery during each of said second time intervals.

14. A apparatus according to claim 13,

wherein said first time intervals are each about 25 ms;

wherein said second time intervals are each about 25 ms; and

wherein said selected time interval is about 2 seconds.

15. A apparatus according to claim 12, wherein said circuit samples a voltage of said battery at a point in time after said selected time interval.

16. A apparatus according to claim 12, wherein said battery is a lithium cell.

17. A method comprising:

periodically sampling a voltage of a battery; and

applying a load to said battery during a selected time interval before each said sampling of said voltage of said battery.

18. A method according to claim 17, wherein said applying of said load is carried out by continuously applying said load to said battery throughout said selected time interval.

19. A method according to claim 18, including selecting said selected time interval to be about 500 ms.

20. A method according to claim 17, including selecting a lithium cell to serve as said battery.