Electricity: measuring and testing – Electrolyte properties – Using a battery testing device
Reexamination Certificate
1999-10-08
2001-09-04
Wong, Peter S. (Department: 2838)
Electricity: measuring and testing
Electrolyte properties
Using a battery testing device
C324S428000
Reexamination Certificate
active
06285191
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the measurement of electrical current and particularly to measuring current in a vehicle using one or both of the cables of a vehicle connected to its battery.
BACKGROUND OF THE INVENTION
In many applications an electrical current has to be measured and monitored. For example, in vehicles having a battery used for various purposes, such as starting an engine or powering electrical systems such as lights and instruments, current is measured and monitored for instrumentation control purposes. For example, U.S. Pat. No. 4,937,523 entitled “Method for Monitoring Automotive Battery Status”, which is assigned to the assignee of the subject application, describes an analysis system in which current is measured and monitored during operation of an automobile to determine capacity, state of charge and certain fault conditions of the vehicle's battery. Such a system can also be used for other types of vehicles, such as aircraft, buses, etc.
One technique for electrical current measurement and/or monitoring the current flow in the electrical systems of automotive, aircraft and other vehicles requires a sensor that effectively measures the magnetic field caused by a current flowing through a conductor. Some of the commonly used sensor types are Hall effect and inductive devices. Another technique, used in the aforesaid patent, is that of a precision resistance shunt of a known resistance value which is placed in series with a part of the conductor carrying the current to be measured. By measuring the voltage across the shunt and knowing its resistance, the current can be calculated.
While the use of a shunt is adequate for many purposes, it has disadvantages in that it requires the cost of the shunt itself and additional electrical connections. More importantly, the shunt results in a power loss which is a product of the square of the current value times the resistance value of the shunt. For example, if a one ohm shunt is used to measure current flow in the electrical system of an automobile, the power loss due to the resistance heating of the shunt would be substantial and could cause unnecessary fuel consumption in the vehicle.
Accordingly, it would be desirable to be able to measure current in a vehicle having a battery without the necessity of using an additional element such as a shunt or another type of sensor.
SUMMARY OF THE INVENTION
The battery used in a vehicle typically has two terminals, one of which is connected to a vehicle electrical reference point (ground) such as its metal chassis and the other to provide the operating voltage to a takeoff supply point. In most vehicles, a cable is provided between each of the battery terminals and its connecting point, such as ground or the vehicle system voltage supply takeoff point. In accordance with one embodiment of the invention, one or both of the battery cables is made to have a known resistance value. For example, a typical value would be 1.0 millohm for the cable connected to the positive battery terminal and 0.1 millohm for the cable connected to the battery negative terminal.
In accordance with the invention, the current flow through a cable connected to the battery into the battery, such as during charging by the vehicles alternator, or the flow from the battery, such as during engine starting or operation of any other vehicle electrical system component, is determined by measuring the voltage across the existing and necessary vehicle cable. The current is determined by measuring the voltage drop across the cable of known resistance value and computing, such as by using a computer, the current by the well known Ohm's law formula I=E/R.
In one embodiment of the invention, a differential current sensor is used. The current sensor is an electronic amplifier type device whose characteristics can be modified to accommodate different current ranges. In a preferred embodiment, to accommodate for the possibility of the cable resistance being different from the desired value and other circuit tolerance variations, an auto-calibration circuit is used which permits an accurate measurement of battery current to be made without the need to know the exact resistance of the cable. Also, provision is made to automatically compensate for component tolerances that would cause an offset when the system input current is zero.
It is therefore an object of the present invention to provide for the monitoring and measurement of current in a vehicle having a battery using one of the existing and necessary battery cables as a part of a sensor arrangement.
In accordance with one aspect of the invention a cable of known resistance value is connected to one of the terminals of a vehicle battery through which current flows is used to provide the input to a differential current sensor to measure and monitor battery current flow.
In accordance with another aspect of the invention a current sensor for a vehicle in which one or both of the cables connected to the vehicle's battery terminals is made to be of a known resistance value and is used as shunt for measuring current.
In accordance with a further aspect of the invention the voltage across a cable connected to one of the terminals of a vehicle battery through which current flows is provided to a circuit for measuring and monitoring the battery current having auto-calibration capability which permits an accurate measurement of the current to be made without the need to know the exact resistance of the cable.
REFERENCES:
patent: 5381097 (1995-01-01), Hirzel
patent: 5444378 (1995-08-01), Rogers
patent: 5589757 (1996-12-01), Klang
patent: 5691078 (1997-11-01), Kozaki et al.
patent: 5847566 (1998-12-01), Marritt et al.
patent: 6037749 (2000-03-01), Parsonage
Gollomp Bernard P.
Kacerek John
Palanisamy Thirumalai G.
Allied-Signal Inc.
Luk Lawrence
Wong Peter S.
Yeadon Loria B.
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