Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – In vehicle wiring
Reexamination Certificate
1999-10-29
2001-09-11
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
In vehicle wiring
Reexamination Certificate
active
06288552
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a sensor for detecting current flow in an electrical conductor, and more particularly to a tester for heated window grids using a giant magnetoresistive (GMR) sensor to generate an output signal from which current flow in the electrical conductors can be determined.
BACKGROUND
Most passenger vehicles include some form of defogger or deicer arranged on the rear window or backlight. The defogger or deicer is implemented by placing a grid along the back window, typically horizontally, using conductive inks printed on the interior of the rear window. An electric current is passed through the grid to generate heat which sufficiently defogs or deices the window.
In order to insure production of a quality vehicle, automobile manufacturers typically test the grid to insure that each individual electrical conductor or line of the grid conducts current to insure proper operation. Because the grid is located on the interior of the window and manufacturers prefer to test the grid after installation of the window to the vehicle body, direct testing of the grid, such as by testing voltage across the end portions of each particular grid line requires assembly personnel to get into the back seat of the vehicle to conduct the test. Manufacturers prefer to avoid having the assembly personnel enter the vehicle to minimize the introduction of dust, debris, and dirt into the vehicle. Such testing can also be time consuming, as it requires that an operator enter the vehicle, conduct a test on each grid line, and exit the vehicle before proceeding to test the grid of the next vehicle having a heater grid. Further, such a process requires an operator strictly dedicated to performing this function.
One approach to making the testing process more efficient is discussed in U.S. Pat. No. 4,395,677, issued Jul. 26, 1993 and assigned to the assignee of the present invention, and which is hereby incorporated by reference. The approach discussed in this patent utilizes a pair of Hall effect sensors to test for current flow through each electrical conductor of the rear window heated grid in order to avoid having assembly personnel enter the vehicle on the assembly line. The solution produced by this system, requires two Hall effect sensors spaced apart a predetermined distance. This system, however, requires that the sensor be passed over the grid within a predetermined range of speeds, outside of which can produce inaccuracies within the system. Further, this system has been found to be sensitive to external magnetic fields introducing possibly inaccurate readings.
Thus, it is an object of the present invention to provide a tester for heated window grids which can be passed over the grid without regard to the speed at which it is passed over the grid.
It is a further object of the present invention to provide a more robust tester for heated window grids which is relatively unaffected by external electromagnetic fields.
SUMMARY OF THE INVENTION
This invention is directed to an apparatus for detecting energization of individual electrical conductors of a plurality of generally parallel, adjacent electrical conductors. The apparatus includes a magnetic sensor which is passed over the electrical conductors. The magnetic sensor generates an output signal in accordance with variation in the magnetic field as the sensor passes over the electrical conductors. A delay element receives the output signal and delays the output signal for a predetermined period to define a delay signal. An adder determines the difference between the output signal and the delay signal to define a difference signal. A high window comparator determines whether the difference signal is above a predetermined threshold and generates a high window signal in accordance with the difference signal. A low window comparator determines whether the difference signal is below a predetermined threshold and generates a low window signal in accordance with the difference signal. A control circuit compares the high window signal and the low window signal and generates an increment signal in accordance with the low and high window signals. A counter receives the increment signal and increments in accordance with the increment signal.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 4217783 (1980-08-01), Ito et al.
patent: 4395677 (1983-07-01), Petersdorf
patent: 4542333 (1985-09-01), Koontz
patent: 4610710 (1986-09-01), Koontz
Calcaterra Mark P.
DaimlerChrysler Corporation
Snow Walter E.
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