Activity-based battery monitor with a universal current measuring apparatus
A battery monitoring apparatus that obtains a current measurement for a current in a conductive element. The battery monitoring apparatus includes conductive lines configured to couple to a conductive element having an electrical current, a filter coupled to the conductive lines and configured to filter noise from a signal derived from a voltage difference between the conductive lines, an analog-to-digital converter that converts the signal filtered by the filter and outputs a digital signal, and a controller that receives the digital signal from the analog-to-digital converter.
1. A battery monitoring apparatus comprising:
conductive lines configured to couple to a conductive element having an electrical current;
a filter coupled to the conductive lines and configured to filter noise from a signal derived from a voltage difference between the conductive lines, wherein the signal represents a current in the conductive element resulting from the voltage difference;
an analog-to-digital converter that converts the signal filtered by the filter and outputs a digital signal;
a meter configured to measure an actual current; and
a controller that receives the digital signal and the measured actual current and computes a correction factor using the received digital signal and the received actual current.
2. The battery monitoring apparatus of claim 1 , wherein the conductive element comprises a direct current (DC) shunt.
3. The battery monitoring apparatus of claim 1 , further comprising an operational amplifier circuit configured to filter the signal filtered by the filter.
4. The battery monitoring apparatus of claim 3 , wherein the filter, the analog-to-digital converter, the controller, and the operational amplifier circuit are located on a current sensing microprocessor card.
5. The battery monitoring apparatus of claim 1 , further comprising a thermistor coupled to the conductive element and configured to measure temperature at the conductive element.
6. The battery monitoring apparatus of claim 5 , wherein the thermistor provides temperature information used by the controller to compute a temperature correction factor according to the formula:
TCF= 1 +TC x ( T−T o )
where T is the measured temperature. T o is the reference temperature at which calibration is performed, and TC x is the temperature coefficient of resistance of the conductive element.
7. The battery monitoring apparatus of claim 1 , wherein the controller computes the correction factor as the received actual current over the received digital signal.
8. The battery monitoring apparatus of claim 1 , wherein the controller is further programmed to perform a calibration procedure by which a multi-point correction line is computed using the received digital signal and the received actual current.
9. The battery monitoring apparatus of claim 1 , wherein the meter is a clamp-on meter.
10. A method for obtaining a current in an activity-based battery monitoring apparatus, the method comprising:
filtering a signal from wires coupled to a conductive element, wherein the signal represents a sensed current resulting from a voltage drop across the conductive element;
converting the signal from an analog form to a digital form; and
performing a calibration procedure by which a correction factor is computed using an actual current measurement and the sensed current.
11. The method of claim 10 , further comprising performing a calibration procedure by which a multi-point correction line is computed from the actual current measurement and the sensed current.
12. The method of claim 10 , further comprising presenting a user interface to read the sensed current and receive the actual current measurement as an input.
13. The method of claim 10 , further comprising correcting the digital form of the signal based on a temperature at the conductive element according to the formula:
TCF= 1 +TC x ( T−T o )
where T is the measured temperature, T o is the reference temperature at which calibration is performed, and TC x is the temperature coefficient of resistance of the conductive element.
14. A battery monitoring apparatus comprising:
(a) a voltage sense input port to which leads extending to a battery may be connected such that a voltage signal representing the voltage across the battery is provided to the voltage sense input port; and
(b) a current sense input port to which leads extending to a universal current measuring apparatus may be connected such that a current signal representing the current through the battery is provided to the universal current measuring apparatus, wherein the universal current measuring apparatus comprises a first filter to remove noise from a received current signal, an analog-to-digital converter to convert the filtered current signal to a digital signal, and a controller programmed to receive an actual current measurement and the digital signal and to compute a correction factor using the received actual current measurement and the received digital signal.
15. The battery monitoring apparatus of claim 14 , further including a temperature sense input port coupled to the universal current measuring apparatus to receive a temperature signal during a battery event.
16. The battery monitoring apparatus of claim 14 , wherein the universal current measuring apparatus is connected in series with the battery to detect a level and direction of current flowing through the battery.
17. The battery monitoring apparatus of claim 14 , wherein the universal current measuring apparatus components are mounted on a printed circuit board.
18. The battery monitoring apparatus of claim 14 , wherein the universal current measuring apparatus is coupled to an amplifier connected to receive the filtered current signal and a second filter to low-pass filter an output signal from the amplifier, and further wherein the analog to digital converter is connected to receive the filtered output signal from the second filter and to convert the received output signal into the digital signal.
19. The battery monitoring apparatus of claim 18 , wherein the amplifier includes a high gain amplifier and a low gain amplifier, each amplifier connected to receive the filtered current signal, and wherein the analog to digital converter includes a first channel connected to receive an output signal from the high gain amplifier and a second channel connected to receive an output signal from the low gain amplifier, the controller further programmed to selectively receive the digital signal from the first analog to digital converter channel when the current signal is below a threshold value and from the second analog to digital converter channel when the current signal is above a threshold value.
20. The battery monitoring apparatus of claim 19 , wherein the high gain amplifier saturates at a selected current level and the controller is programmed to select data from the second analog to digital converter channel when the digital signal from the first analog to digital converter channel is at the saturation level of the high gain amplifier.
21. The battery monitoring apparatus of claim 14 , wherein the controller is further programmed to store one or more stationary data fields in a non-volatile memory selected from the group consisting of installation time, high voltage setpoint, low voltage setpoint, high current setpoint, high temperature setpoint, battery nominal capacity in ampere hours, battery nominal voltage, a cycle counter, total hours of open circuit overall events, total hours of discharge overall events, total hours of charge overall events, total amp-hours of discharge overall events, total amp-hours of charge overall events, and a count of the number of events recorded.
22. The battery monitoring apparatus of claim 21 , wherein the controller is further programmed to store all of the stationary data fields from the group of stationary data fields.
23. The battery monitoring apparatus of claim 14 , wherein the controller is programmed to perform a calibration procedure by which a multi-point correction line is computed using the received digital signal and the received actual current measurement.
24. The battery monitoring apparatus of claim 14 , further comprising a thermistor configured to measure a temperature.
25. The battery monitoring apparatus of claim 24 , wherein the controller is further programmed to compute a temperature correction factor according to the formula:
TCF= 1 +TC x ( T−T o )
where T is the measured temperature, T o is the reference temperature at which calibration is performed, and TC x is the temperature coefficient of resistance of the conductive element.