Method and apparatus for detecting a battery voltage

• US 7,911,182 B2
• Filed: 05/27/2005
• Issued: 03/22/2011
• Est. Priority Date: 05/27/2005
• Status: Active Grant

• Current Assignee: Savi Technology Incorporated
• Original Assignee: Savi Technology Incorporated
• Inventors: Cargonja, Nikola, Chan, Joseph S., Ahn, Don H.
• Primary Examiner(s): Tso, Edward
• Assistant Examiner(s): PIGGUSH, AARON C
• Application Number:
  US11/140,586
• Publication Number:
  US 20060267555A1
• Time in Patent Office: 2,125 Days
• Field of Search: 320/132, 320/133, 320/134, 320/136, 320/138
• US Class Current: 320/133
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: H02J 7/0047 with monitoring or indicating devices or circuits

Abstract

One aspect of the invention involves: maintaining a record of how long a circuit operates in each of a plurality of different operating modes thereof, starting from a point in time at which a battery that powers the circuit is replaced; calculating for each of the operating modes as a function of the record a cumulative current drain from the point in time to a current time; and determining as a function of the cumulative current drains whether the battery is subject to a low voltage condition. Another aspect involves: monitoring a voltage of a battery; periodically determining whether the voltage of the battery is subject to a low voltage condition; and maintaining a count of the number of times that the determining results in a determination that the battery is subject to a low voltage condition.

Claims

1. An apparatus comprising a battery and a circuit powered by said battery that has a plurality of different operating, modes, wherein said circuit:

operates in each of said operating modes, starting from a point in time at which said battery is substantially fully charged, said circuit operating in one of said operating modes during each of a plurality of different time intervals that are spaced from each other in time;

maintains a record of how long said circuit operates in each of said operating modes, starting from said point in time;

calculates for each of said operating modes as a function of said record a cumulative current drain out of said battery from said point in time to a current time; and

determines as a function of said cumulative current drains whether said battery presently has a low voltage condition;

wherein said apparatus includes a radio frequency identification tag, said circuit and said battery being portions of said tag;

wherein said tag has an antenna; and

wherein said circuit has 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 has a low battery condition.

2. An apparatus according to claim 1, wherein said battery is a lithium cell.

3. An apparatus according to claim 1, wherein said circuit:

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

determines that said battery presently has a low voltage condition when said rate of voltage decrease exceeds said threshold.

4. An apparatus according to claim 1, wherein said circuit:

determines a respective current drain rate for each of said operating modes; and

carries out said calculating of respective said cumulative current drains as a function of respective said current drain rates.

5. An apparatus according to claim 1, wherein said circuit effects said determining of whether said battery presently has a low voltage condition in a manner that includes evaluating a discharge specification for said battery in relation to current drain information that is a function of said cumulative current drains.

6. An apparatus comprising a battery and a circuit powered by said battery that has a plurality of different operating modes, wherein said circuit:

operates in each of said operating modes, starting from a point in time at which said battery is substantially fully charged, said circuit operating in one of said operating modes during each of a plurality of different time intervals that are spaced from each other in time;

maintains a record of how long said circuit operates in each of said operating modes, starting from said point in time;

calculates for each of said operating modes as a function of said record a cumulative current drain out of said battery from said point in time to a current time;

determines as a function of said cumulative current drains whether said battery presently has a low voltage condition;

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

determines that said battery presently has a low voltage condition when said rate of voltage decrease exceeds said threshold;

wherein said circuit effects said evaluation of said rate of decrease of said voltage by;

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 the calculated difference to said threshold.

7. An apparatus comprising a battery and a circuit powered by said battery that has a plurality of different operating modes, wherein said circuit:

operates in each of said operating modes, starting from a point in time at which said battery is substantially fully charged, said circuit operating in one of said operating modes during each of a plurality of different time intervals that are spaced from each other in time;

maintains a record of how long said circuit operates in each of said operating modes, starting from said point in time;

calculates for each of said operating modes as a function of said record a cumulative current drain out of said battery from said point in time to a current time; and

determines as a function of said cumulative current drains whether said battery presently has a low voltage condition;

wherein said apparatus includes a radio frequency identification tag, said circuit and said battery being portions of said tag;

wherein said circuit has a transmitter and a receiver; and

wherein said operating modes of said circuit include a transmit mode in which said transmitter is enabled and said receiver is disabled, a receive mode in which said transmitter is disabled and said receiver is enabled, and a standby mode in which said transmitter and receiver are both disabled.

8. A method comprising:

operating a circuit in each of a plurality of different operating modes, starting from a point in time at which a battery that powers said circuit is substantially fully charged, including operating said circuit in one of said operating modes during each of a plurality of different time intervals that are spaced from each other in time;

causing said circuit to maintain a record of the cumulative amount of time that said circuit has operated in each of said operating modes, starting from said point in time;

calculating for each of said operating modes as a function of said record a cumulative current drain out of said battery from said point in time to a current time;

determining as a function of said cumulative current drains whether said battery presently has a low voltage condition;

providing a radio frequency identification tag, said circuit being a portion of said tag; and

configuring said tag to have an antenna and said circuit to have 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 has a low battery condition.

9. A method according to claim 8, including:

determining a respective current drain rate for each of said operating modes; and

carrying out said calculating of respective said cumulative current drains as a function of respective said current drain rates.

10. A method according to claim 8, wherein said

determining includes evaluating a discharge specification for said battery in relation to current drain information that is a function of said cumulative current drains.

11. A method according to claim 8, including selecting a lithium cell to serve as said battery.

12. A method according to claim 8, including:

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

indicating that said battery presently has a low voltage condition when said rate of voltage decrease exceeds said threshold.

13. A method comprising:

operating a circuit in each of a plurality of different operating modes, starting from a point in time at which a battery that powers said circuit is substantially fully charged, including operating said circuit in one of said operating modes during each of a plurality of different time intervals that are spaced from each other in time;

causing said circuit to maintain a record of the cumulative amount of time that said circuit has operated in each of said operating-modes, starting from said point in time;

calculating for each of said operating modes as a function of said record a cumulative current drain out of said battery from said point in time to a current time;

determining as a function of said cumulative current drains whether said battery presently has a low voltage condition;

providing a radio frequency identification tag, said circuit being a portion of said tag configuring said circuit to have a transmitter and a receiver; and

configuring said operating modes of said circuit to include a transmit mode in which said transmitter is enabled and said receiver is disabled, a receive mode in which said transmitter is disabled and said receiver is enabled, and a standby mode in which said transmitter and receiver are both disabled.

14. A method comprising:

operating a circuit in each of a plurality of different operating modes, starting from a point in time at which a battery that powers said circuit is substantially fully charged, including operating said circuit in one of said operating modes during each of a plurality of different time intervals that are spaced from each other in time;

causing said circuit to maintain a record of the cumulative amount of time that said circuit has operated in each of said operating modes, starting from said point in time;

calculating for each of said operating modes as a function of said record a cumulative current drain out of said battery from said point in time to a current time;

determining as a function of said cumulative current drains whether said battery presently has a low voltage condition;

evaluating whether a rate of voltage decrease of said battery is in excess of a threshold, wherein said evaluating includes;

tracking the drain of charge from said battery;

indicating that said battery presently has a low voltage condition when said rate of voltage decrease exceeds said threshold;

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 the calculated difference to said threshold.

15. A method according to claim 14, including providing a radio frequency identification tag, said circuit being a portion of said tag.