Methods and apparatus for magnetic article detection
First Claim
1. Apparatus for detecting passing magnetic articles and providing a magnetic article detector output signal indicative of the passing magnetic articles comprising:
- a magnetic field sensor providing a signal proportional to an ambient magnetic field;
a first circuit responsive to the magnetic field sensor signal to provide a first output signal indicative of the passing magnetic articles, wherein the first output signal provides the magnetic article detector output signal during a first time interval;
a second circuit responsive to the magnetic field sensor signal to provide a second output signal indicative of the passing magnetic articles, wherein the second output signal provides the magnetic article detector output signal during a second time interval following the first time interval;
a phase comparator responsive to the first output signal and the second output signal to provide a control signal indicative of a change of a phase relationship between the first output signal and the second output signal; and
a switch having a first input responsive to the first output signal, a second input responsive to the second output signal, and an output at which the magnetic article detector output signal is provided, wherein the switch is controlled by the control signal.
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Abstract
Apparatus and methods for detecting passing magnetic articles using a first, True Power On State (TPOS) detector during a first time interval and transitioning to a second, running mode detector after the first time interval, when the output of the second detector is accurate. A phase comparator is responsive to the output signal of the first and second detectors and provides a control signal indicative of a change in the phase relationship between the two output signals. An output switch controlled by the phase comparator provides, as the detector output signal, the first detector output signal during the first time interval and the second detector output signal thereafter. A threshold signal associated with the TPOS detector is at a fixed level during a first portion of the first time interval and is adjusted during a second portion of the first time interval in response to an automatic gain control circuit in order to reduce the phase error associated with transitioning from the TPOS detector to the running mode detector. Also described are apparatus and methods for updating a running mode threshold signal that is a percentage of the peak-to-peak magnetic field sensor signal, so that unnecessary update events are reduced.
137 Citations
19 Claims
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1. Apparatus for detecting passing magnetic articles and providing a magnetic article detector output signal indicative of the passing magnetic articles comprising:
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a magnetic field sensor providing a signal proportional to an ambient magnetic field; a first circuit responsive to the magnetic field sensor signal to provide a first output signal indicative of the passing magnetic articles, wherein the first output signal provides the magnetic article detector output signal during a first time interval; a second circuit responsive to the magnetic field sensor signal to provide a second output signal indicative of the passing magnetic articles, wherein the second output signal provides the magnetic article detector output signal during a second time interval following the first time interval; a phase comparator responsive to the first output signal and the second output signal to provide a control signal indicative of a change of a phase relationship between the first output signal and the second output signal; and a switch having a first input responsive to the first output signal, a second input responsive to the second output signal, and an output at which the magnetic article detector output signal is provided, wherein the switch is controlled by the control signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. Apparatus for detecting passing magnetic articles and providing a magnetic article detector output signal indicative of the passing magnetic articles comprising:
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a magnetic field sensor providing a signal proportional to an ambient magnetic field; a first circuit responsive to the magnetic field sensor signal to provide a first output signal indicative of the passing magnetic articles, wherein the first output signal provides the magnetic article detector output signal during a first time interval, wherein the first circuit comprises a comparator having a first input responsive to the magnetic field sensor signal and a second input responsive to a threshold signal and an output at which the first output signal is provided, wherein the threshold signal is adjustable; and a second circuit responsive to the magnetic field sensor signal to provide a second output signal indicative of the passing magnetic articles, wherein the second output signal provides the magnetic article detector output signal during a second time interval following the first time interval. - View Dependent Claims (11, 12, 13, 14)
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15. A method for detecting passing magnetic articles and providing a magnetic article detector output signal indicative of the passing magnetic articles, comprising:
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providing a magnetic field signal proportional to an ambient magnetic field; detecting the passing magnetic articles with a first detector that is responsive to the magnetic field signal to provide a first detector output signal, wherein the first detector output signal provides the magnetic article detector output signal during a first time interval; detecting the passing magnetic articles with a second detector that is responsive to the magnetic field signal to provide a second detector output signal, wherein the second detector output signal provides the magnetic article detector output signal during a second time interval following the first time interval; and transitioning from the first time interval to the second time interval in response to a change in the phase relationship between the first detector output signal and the second detector output signal. - View Dependent Claims (16, 17, 18, 19)
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Specification