Detection of passing magnetic articles with a peak referenced threshold detector

A detector for detecting passing magnetic articles comprising:

• a magnetic-field-to-voltage transducer having an output at which an analog voltage, Vsig, is generated, said Vsig voltage being commensurate to the strength of the ambient magnetic field and having at least one peak;
• an analog-to-digital converter coupled to the output of said transducer and operative to convert to a corresponding digital signal at least a portion of said Vsig voltage, which portion includes said peak;
• and
• a circuit coupled to said analog-to-digital converter and operative to generate an output signal indicative of the occurrence of the times t.sub.xpk when the difference between Vsig and said peak of Vsig has exceeded a predetermined amount.

A method for detection of passing magnetic articles comprising the steps of:

• a) sensing an ambient magnetic field that is influenced by the passing of magnetic articles and generating a voltage, Vsig, that is commensurate to the magnetic field, wherein Vsig has positive excursions, negative excursions, and peak excursions;
• b) converting at least a portion of the analog signal Vsig to a digital signal Vcount;
• c) at a peak excursion in Vsig, remembering Vcount;
• and
• d) when, at time t.sub.xpk after a peak in Vsig, Vsig has varied from the remembered Vcount by a predetermined amount, producing an output signal indicating the detection of a passing magnetic article.