Digital loop detector with automatic tuning
First Claim
1. In a digital device for detecting a metal object in the field of influence of a detector loop controlling an oscillator, said digital device including means for creating a series of counting intervals;
- pulse counting means for counting pulses during a current counting interval, with the magnitude of the pulse count during an interval being indicative of metal detected by said loop;
means for storing a pulse count of a prior counting interval; and
means for indicating a detection when said pulse count of a current interval differs from said stored pulse count by at least a selected amount, the improvement comprising;
reading means for creating a signal when said pulse count of a counting interval differs in a selected numerical direction from a selected count magnitude, and shifting means responsive to said signal for shifting the length of subsequent counting intervals toward a length producing a pulse count including said selected count magnitude.
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Accused Products
Abstract
A digital device for detecting a metal object in the field of influence of a detector loop controlled by an oscillator which device creates a series of counting intervals and counts pulses during the intervals. The magnitude of the count during an interval is then indicative of metal detected by the loop. The count of a prior counting interval is stored and compared with the count of the next interval to determine whether or not there has been a detection. In this type of device there is provided an improvement wherein the magnitude of the counts stored during an interval is used to change the length of subsequent counting intervals. This maintains a generally high count magnitude for the counting interval to improve the sensitivity of the detecting device.
31 Citations
25 Claims
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1. In a digital device for detecting a metal object in the field of influence of a detector loop controlling an oscillator, said digital device including means for creating a series of counting intervals;
- pulse counting means for counting pulses during a current counting interval, with the magnitude of the pulse count during an interval being indicative of metal detected by said loop;
means for storing a pulse count of a prior counting interval; and
means for indicating a detection when said pulse count of a current interval differs from said stored pulse count by at least a selected amount, the improvement comprising;
reading means for creating a signal when said pulse count of a counting interval differs in a selected numerical direction from a selected count magnitude, and shifting means responsive to said signal for shifting the length of subsequent counting intervals toward a length producing a pulse count including said selected count magnitude. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
- pulse counting means for counting pulses during a current counting interval, with the magnitude of the pulse count during an interval being indicative of metal detected by said loop;
Specification