Electricity: measuring and testing – Conductor identification or location – Inaccessible
Reexamination Certificate
1999-03-26
2001-03-06
Snow, Walter (Department: 2862)
Electricity: measuring and testing
Conductor identification or location
Inaccessible
C324S671000
Reexamination Certificate
active
06198271
ABSTRACT:
BACKGROUND
This invention relates to sensors suitable for locating objects positioned behind or within a volume of material, and in particular to a wall-stud sensor.
U.S. Pat. No. 4,464,622, issued Aug. 7, 1984, discloses an electronic sensor for locating objects, such as wall studs, positioned behind wall surfaces. That sensor detects the edges of studs by measuring changes in the capacitance of a wall due to the presence or absence of a stud as the sensor is moved along the wall surface.
That sensor includes capacitive plates, or elements, connected to circuits that detect changes in the capacitance of those elements. As the sensor is moved along a wall, any such capacitive changes are presumably due to changes in the dielectric constant of the wall; increased capacitance is generally associated with the presence of a wall stud.
While this sensor works well to locate the edges of studs within most walls, experience has shown that its performance could be improved in several respects. For example, the precision with which that sensor locates a given stud edge depends upon various extraneous factors that affect wall capacitance, such as the thickness of the wall covering material, the dielectric constant of the wall covering material and the stud, the ambient humidity, and the temperature of the electronics within the sensor. Variances in some of these factors are compensated for by calibrating the sensor prior to each use by placing the sensor against the wall covering material at a place behind which there is presumed to be no stud. However, such calibration does not completely compensate for such variances. For example, changes in the thickness of wall covering thickness change the perceived location of stud edges. Furthermore, the calibration may be erroneous if there is a stud adjacent or partially adjacent the sensor during calibration. Accordingly, there is a need for a sensor that is easier to calibrate and less sensitive to variations in extraneous parameters that affect wall capacitance, particularly various wall thicknesses.
SUMMARY
The present invention is directed to an easily calibrated sensor that is relatively insensitive to variations in extraneous factors that affect wall capacitance. The sensor includes a comparison circuit connected to each of three capacitive elements. As the sensor is moved along a wall, the comparison circuit monitors the relative charge time of three capacitive elements, the charge times providing an indication of the relative capacitances of the three capacitive elements. As the sensor is moved along a wall, changes in the relative capacitances of the three elements will occur in the presence of a hidden stud as a result of changes in the dielectric constant of the wall. The comparison circuit uses differences in the measured relative capacitances of the first, second, and third capacitive elements to locate the stud. Finally, the sensor includes an intuitive “window” display that simplifies the task of locating a stud by providing a user with an image of the hidden stud as the sensor is moved over the stud.
This summary does not purport to define the invention. The invention is defined by the claims.
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Dodd Paul W.
Heger Charles E.
Klivans Norman R.
Skjerven Morrill & MacPherson LLP
Snow Walter
Zircon Corporation
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