Detection of passing magnetic articles while periodically adapting detection threshold

A magnetic article proximi detector comprising:

• a magnetic field-to-voltage transducer providing a voltage output signal, Vsig, proportional to a magnetic field;
• a threshold voltage generator operative to generate a threshold voltage that is a percentage of the peak-to-peak voltage of Vsig, wherein the threshold voltage is periodically updated in each of a plurality of update time intervals to remain the percentage, within a predetermined tolerance, of the peak-to-peak voltage of Vsig in response to changes that may occur in the peak voltages of Vsig, wherein each of the update time intervals encompasses a plurality of positive peaks in Vsig;
• and
• a comparator comparing Vsig to the threshold voltage to generate a proximity detector output voltage that becomes one binary level when Vsig rises to exceed the threshold voltage and another binary level when Vsig falls to below the threshold voltage.

A method for detection of passing magnetic articles comprising;

• a) sensing an ambient magnetic field and generating a voltage, Vsig, that is proportional to the magnetic field;
• b) generating threshold voltages V.sub.Pth and V.sub.Nth referred, respectively, to the positive and negative peaks of Vsig and that are respectively fixed percentages of the peak to peak voltage in Vsig at the beginning of, each of a succession of update time intervals;
• c) generating a proximity-detector output voltage that becomes one binary level when Vsig rises to exceed V.sub.Pth and that becomes another binary level when Vsig falls to below V.sub.Nth ;
• and
• d) periodically updating in each of a plurality of update time intervals the threshold voltages V.sub.Pth and V.sub.Nth to remain the fixed percentage, within a predetermined tolerance, of the peak-to-peak voltage of Vsig in response to changes that may occur in the peak voltages of Vsig, wherein each of the update time intervals encompasses a plurality positive peaks in Vsig.

A method for detection of passing magnetic articles comprising:

• a) sensing an ambient magnetic field and generating a voltage, Vsig, that is proportional to the magnetic field;
• b) generating threshold voltages V.sub.Pth and V.sub.Nth to be fixed percentages of the peak to peak voltage in Vsig at the beginning of each of a succession of update time intervals, each of the update time intervals encompassing a plurality of positive peaks in Vsig;
• c) generating a proximity-detector binary output voltage that becomes high when Vsig rises to exceed V.sub.Pth and that becomes low when Vsig falls to below V.sub.Nth ;
• d) generating a signal voltage V.sub.Pold that is equal to the first positive peak in Vsig, at the beginning of the first update time interval, and holding the voltage V.sub.Pold during the first update time interval;
• e) generating a signal voltage V.sub.Pnew that is equal to the highest positive peak voltage in Vsig during the each update time interval, and holding the voltage V.sub.Pnew ;
• f) at the end of each update time interval, generating a binary voltage, Vupdt, that is momentarily high when V.sub.Pnew lies outside the range V.sub.Pold -.DELTA.to V.sub.POld +.DELTA.v, where .DELTA.v is an incremental DC bias voltage;
• generating a signal voltage V.sub.NOld that is equal to the first negative peak in Vsig, at the beginning of the first update time interval, and holding the voltage V.sub.Nold during the first update time interval;
• h) generating a signal voltage V.sub.Nnew, that is equal to the lowest negative peak voltage in Vsig during the each update time interval, and holding the voltage V.sub.Nnew ;
• i) at the end of each update time interval, generating a momentary high in the binary voltage, Vupdt, when V.sub.Nnew lies outside the range V.sub.NOld -.DELTA.v to V.sub.Nold +.DELTA.v, where .DELTA.v is an incremental DC bias voltage;
• j) when Vupdate goes momentarily high, changing the signal voltages V.sub.Pold and V.sub.Nold to equal respectively the voltages V.sub.Pnew and V.sub.Nnew at the end of the preceding update time interval and holding the voltages V.sub.Pold and V.sub.Nold until the end of the each update time interval so that the threshold voltages V.sub.Pth and V.sub.Nth have the fixed percentages of the updated peak-to-peak voltage V.sub.Pold -V.sub.Nold.