Process and apparatus for determining the state of charge of a battery

• US 4,433,295 A
• Filed: 01/08/1982
• Issued: 02/21/1984
• Est. Priority Date: 01/05/1981
• Status: Expired due to Fees

• Current Assignee: Montres Rolex SA (Rolex SA)
• Original Assignee: Montres Rolex SA (Rolex SA)
• Inventors: Zaugg, Edmond
• Primary Examiner(s): Tokar, Michael J.
• Application Number:
  US06/338,153
• Time in Patent Office: 774 Days
• Field of Search: 324/425, 324/426, 324/427, 324/429, 324/430, 324/433, 320/48
• US Class Current: 324/429
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: G04C 10/04 with means for indicating the condition of the power supply in general G01R31/36
• CPC Class Codes: Y10S 320/21 State of charge of battery

Abstract

A process and apparatus for determining the state of discharge of an electric battery by measuring the voltage drop associated with changes in its internal resistance. According to the process, the battery is periodically connected to a reference load for a brief interval during which the voltage at the terminals of the load is measured. The measured analog voltage is converted to a digital signal which is compared to a number of pre-programmed digital levels to determine the state of change of the battery. The apparatus comprises a commutation component controlled by a logic signal, a reference load, a sampler-and-hold circuit, an analog-to-digital converter and a comparator which can be programmed at n levels. The apparatus compares digital signals corresponding to the voltage at the terminals of the reference load with the n programmed levels of the decoder and a signal is generated indicating the level of the electric battery with respect to the levels programmed into the comparator.

Claims

1. A process for determining the state of charge of a battery supplying electrical power to an instrument of the type which includes a current consuming component having at least two consumption levels, one of said levels being a minimum current consumption level defined as a minimum load and a second of said levels being a maximum consumption level defined is a maximum load, said process comprising the steps of:

(a) monitoring the load condition of said current consuming component to determine if it presents said minimum or said maximum load to said battery;

(b) periodically connecting said battery to a reference load but only when said current consuming component presents said minimum load to said battery;

(c) sampling the voltage across said reference load when said battery is connected to said reference load;

(d) comparing the sampled voltage to a number of predetermined voltage levels each which correspond to a different state of charge of the battery so as to determine the state of charge of the battery; and

(e) generating at least one output signal which indicates a state of charge of the battery as determined by said comparing step.

2. The process of claim 1 in which the sampled voltage is converted to a digital signal and the digital signal is compared to a number of predetermined digital signals which correspond to said predetermined voltage levels.

3. The process of claim 1 in which the sampled voltage is converted to a digital signal by the process of:

(a) sampling and storing in analog form a voltage signal generated when said battery is applied to said reference load; and

(b) converting the stored voltage to a digital signal using an analog-to-digital converter.

4. The process of claim 3 in which said reference load is selected to draw a current such that said current drawn from said battery by said reference load and said minimum load is approximately equal said current drawn by the maximum load.

5. An apparatus determining the state of charge of a battery supplying electrical power to an instrument of the type which includes a current consuming component having at least two consumption levels, one of said levels being a minimum current consumption level defined as a minimum load and a second of said levels being a maximum consumption level defined as a maximum load, the apparatus comprising:

(a) means for monitoring the load condition of said current consuming component to determine if it presents said minimum or said maximum load to said battery;

(b) means for periodically connecting said battery to a reference load but only when said current consuming component presents said minimum load to said battery;

(c) means for sampling the voltage across said reference load when said battery is connected to said reference load;

(d) means for comparing said sampled voltage to a number of predetermined voltage levels each of which correspond to a different state of charge of said battery so as to determine the state of charge of said battery; and

(e) means for generating at least one output signal which indicates the state of charge of said battery as determined by said comparing step.

6. The apparatus of claim 5 further comprising means for converting said sampled voltage to a digital signal and means for providing a number of programmed digital signal to which said digital signal is compared.

7. The apparatus of claim 6 in which the means for converting the sampled voltage to digital form comprises:

(a) means for sampling and storing in analog form the voltage generated by the battery; and

(b) an analog-to-digital converter for converting said sampled voltage to digital form.

8. The apparatus of any one of claims 5 through 7 in which the reference load is selected to draw a current such that said current drawn from the battery by said reference load and said minimum load is approximately equal said current drawn by said maximum level.

9. The apparatus of any one of claims 6 or 7 further comprising at least one group of switches which may be used to program one of said predetermined digital signals.

10. The apparatus of any one of claims 6 or 7 further comprising:

(a) several groups of switches, each said group being used to program one of said predetermined digital signals; and

(b) means for generating a number of said output signals, the number of said output signals being equal to or less than the number of said predetermined digital signals.

11. The apparatus of any one of claims 6 or 7 comprising two groups of switches, one of said groups being used to program a pre-alarm level and the other being used to program an alarm level.

12. The apparatus of any one of claims 5 through 7 further comprising a control logic component adapted to supply at least one control logic signal to the means for periodically connecting the battery to the reference load.

13. The apparatus of claim 12 in which the control logic component activates said apparatus at predetermined instances unless said current consuming component presents said maximum load to said battery at that instance.

14. The apparatus of claim 12 in which the control logic prohibits said apparatus from being activated any time during which said current consuming component presents a load greater than minimum load.

15. The apparatus of claim 12 in which the control logis logic prohibits the apparatus from being activated any time during which the current consuming component presents a maximum load.

16. The apparatus of any one of claims 5 through 7 in which said reference load comprises at least one resistance.

17. The apparatus of any one of claims 5 through 7 in which said reference load comprises at least one diode and at least one resistance.

18. The apparatus of any one of claims 5 through 7 in which said reference load comprises at least one element having a resistance value which varies with temperature in a predetermined fashion.

19. The apparatus of any one of claims 5 through 7 further comprising indicating components responsive to said output signals for providing alarms to the user of the instrument.

20. An apparatus for determining the state of charge of a battery supplying electrical power to an instrument of the type which includes a current consuming component having at least two consumption levels, one of said levels being a minimum current consumption level defined as a minimum load and a second of said levels being a maximum consumption level defined as a maximum load, the apparatus comprising:

(a) means for periodically connecting said battery to a reference load when said current consuming component presents said minimum load to said battery;

(b) means for sampling the voltage across said reference load when said battery is connected to said reference load;

(c) means for comparing said sample voltage to a number of predetermined voltage levels each of which correspond to a different state of charge of said battery so as to determine the state of charge of said battery; and

(d) means for generating at least one output signal which indicates the state of charge of said battery as determined by said comparing means, said reference load being selected to draw a current such that the current drawn from said battery by said reference load and said minimum load is approximately equal to the current drawn by said maximum load.

21. The apparatus of claim 20 further comprising means for converting said sampled voltage to a digital signal and means for providing a number of programmed digital signal to which said digital signal is compared.

22. The apparatus of claim 21 in which the means for converting the sampled voltage to digital form comprises:

(a) means for sampling and storing in analog form the voltage generated by the battery; and

(b) an analog-to-digital converter for converting said sampled voltage to digital form.