Methods and apparatus for dynamic offset adjustment in a magnetic article detector
First Claim
1. Apparatus for detecting passing magnetic articles and providing a detector output signal indicative of the passing magnetic articles comprising:
- a magnetic field sensor providing a magnetic field signal proportional to an ambient magnetic field;
an offset adjustment circuit responsive to the magnetic field signal for adjusting an offset of the magnetic field signal based on a dynamically adjustable offset threshold signal to provide an offset-adjusted signal;
a Positive Digital-to-Analog converter (PDAC) operative to provide a PDAC signal that tracks positive peaks of the offset-adjusted signal;
a Negative Digital-to-Analog converter (NDAC) operative to provide an NDAC signal that tracks negative peaks of the offset-adjusted signal; and
a comparator responsive to the offset-adjusted signal and a switching threshold signal to provide the detector output signal, wherein the switching threshold signal is a percentage of the difference between the PDAC signal and the NDAC signal.
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Accused Products
Abstract
Apparatus and methods for detecting passing magnetic articles including an offset adjustment circuit for adjusting the DC level of the magnetic field signal based on a dynamically adjustable offset threshold signal. The detector includes a PDAC for tracking the positive peaks of a magnetic field signal and an NDAC for tracking the negative peaks of the magnetic field signal. In one embodiment, the offset threshold signal includes a positive offset threshold signal and a negative offset threshold signal that are initially set at fixed respective signal levels and that become the level of the PDAC signal and NDAC signals, respectively, in response to a counter, that counts a number of increments of the PDAC signal and decrements of the NDAC signal, reaching a predetermined count value.
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Citations
12 Claims
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1. Apparatus for detecting passing magnetic articles and providing a detector output signal indicative of the passing magnetic articles comprising:
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a magnetic field sensor providing a magnetic field signal proportional to an ambient magnetic field; an offset adjustment circuit responsive to the magnetic field signal for adjusting an offset of the magnetic field signal based on a dynamically adjustable offset threshold signal to provide an offset-adjusted signal; a Positive Digital-to-Analog converter (PDAC) operative to provide a PDAC signal that tracks positive peaks of the offset-adjusted signal; a Negative Digital-to-Analog converter (NDAC) operative to provide an NDAC signal that tracks negative peaks of the offset-adjusted signal; and a comparator responsive to the offset-adjusted signal and a switching threshold signal to provide the detector output signal, wherein the switching threshold signal is a percentage of the difference between the PDAC signal and the NDAC signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for detecting passing magnetic articles by comparing a magnetic field sensor signal proportional to an ambient magnetic field to a switching threshold signal, comprising:
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adjusting a DC offset of the magnetic field sensor signal based on a dynamically adjustable offset threshold signal to provide an offset-adjusted signal; generating a PDAC signal that tracks positive peaks of the offset-adjusted signal; generating an NDAC signal that tracks negative peaks of the offset-adjusted signal; providing a switching threshold signal as a percentage of the difference between the PDAC signal and the NDAC signal; comparing the switching threshold signal to the offset-adjusted signal to provide a detector output signal. - View Dependent Claims (9, 10, 11, 12)
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Specification