Automotive current sensor

• US 5,426,416 A
• Filed: 10/19/1992
• Issued: 06/20/1995
• Est. Priority Date: 10/19/1992
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Corporation
• Original Assignee: Westinghouse Electric Company LLC
• Inventors: Naviasky, Eric H., Jefferies, Daniel W., Henderson, Joseph G., Grone, Donald J.
• Primary Examiner(s): Hofsass, Jeffery A.
• Time in patent office: 974 Days
• Field of Search: 340/664, 340/641, 340/642, 340/635, 340/455, 340/458, 340/657, 307/494, 361/86, 361/87, 361/91, 361/93
• US Class Current: 340/664
• CPC Class Codes: G01R 1/203 Resistors used for electric measuring, e.g. decade resistors standards, resistors for comparators, series resistors, shunts resistors in general H01C; microwave or radiowave terminations H01P1/26; coupling devices H01R
• CPC Class Codes: G01R 15/146 Measuring arrangements for current not covered by other subgroups of G01R15/14, e.g. using current dividers, shunts, or measuring a voltage drop if no voltage isolation is involved G01R1/203 or G01R19/0092
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G01R 31/006 on road vehicles, e.g. automobiles or trucks testing of ignition installations peculiar to internal combustion engines F02P17/00

Abstract

A high-amperage current sensor is disclosed which is suitable for use in an automotive electrical system and which is operatively unaffected by changes in ambient temperature. The current sensor utilizes a shunt assembly having at least one low-resistance shunt element connectable in line between a source of electrical energy and a load. Circuitry preferably configured on an application specific integrated circuit measures voltage drop across the shunt element due to current flow. As a result, an output signal is produced which may be fed to external circuitry for further processing. In presently preferred embodiments, the sensor may comprise analog circuitry producing an analog output signal and/or digital circuitry producing a digital output signal.

Claims

1. An essentially temperature invarient current sensor suitable for use in an automobile to measure a current delivered from a source of electrical energy to a load and configured upon occurrence of internal failure to indicate a maximum current level, said sensor comprising:

a shunt assembly connectable in line with said source and said load, said shunt assembly having at least one low-resistance shunt element constructed of a material having characteristically small resistance drift due to variations in ambient temperature;

a difference mode amplifier having a first input electrically connected to a first terminal side of said shunt and a second input electrically connected to a second terminal side of said shunt element, said difference mode amplifier producing a difference signal representative of a voltage drop across said shunt element due to a flow of current;

said difference mode amplifier further including means for producing upon disconnection of said first and second inputs from said shunt element a voltage difference sufficient to indicate said maximum current level;

scaling circuitry electrically connected to receive said difference signal and operable to produce during normal operation of said difference mode amplifier a ratiometric current level signal; and

said scaling circuitry further operable during failure of said difference mode amplifier to produce a signal indicating said maximum current level.

2. The current sensor of claim 1 further comprising a buffer amplifier having a high impedance input electrically connected to receive said ratiometric current level signal and operable to produce at a low impedance output a current level output signal.

3. The current sensor of claim 2 further comprising means electrically connected to said low impedance output for indicating said maximum current level upon failure of said buffer amplifier.

4. The current sensor of claim 1 wherein said at least one low resistance shunt element is constructed of manganin.

5. The current sensor of claim 1 further comprising transient suppression means electrically connected to said first and second inputs of said difference mode amplifier for limiting a voltage difference thereacross to a preselected maximum.

6. The current sensor of claim 5 wherein said transient suppression means comprises first and second transient suppression networks respectively connected between said first and second inputs and a ground reference, each of said first and second transient suppression networks having, in parallel, a zener diode and a capacitor.

7. The current sensor of claim 1 wherein said scaling circuitry comprises:

a first, a second and a third resistor connected in series between a positive no-current voltage and a negative power supply voltage;

a first nodal connection between said second and third resistors electrically connected to receive said difference signal; and

said current level signal being produced at a second nodal connection between said first and second resistors.

8. The current sensor of claim 7 wherein said scaling circuitry further comprises a diode connected in reverse bias arrangement between said second nodal connection and a ground reference.