Patent ID: 7548056
Filing Date: 2009-06-16
Classification: G01D,G01P

Abstract:
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 positive digital to analog converter (PDAC) operative to provide a PDAC signal that tracks positive peaks of the magnetic field sensor signal, wherein the PDAC signal increases in response to increasing positive peaks of the magnetic field sensor signal and wherein the PDAC signal decreases in response to a predetermined number of positive peaks of the magnetic field sensor signal occurring that are less than a positive update threshold signal; a negative digital to analog converter (NDAC) operative to provide an NDAC signal that tracks negative peaks of the magnetic field sensor signal, wherein the NDAC signal decreases in response to decreasing negative peaks of the magnetic field sensor signal and wherein the NDAC signal increases in response to a predetermined number of negative peaks of the magnetic field sensor signal occurring that are greater than a negative update threshold signal; and a comparator having a first input responsive to the magnetic field sensor signal, a second input responsive to a threshold signal, and an output at which the detector output signal is provided, wherein the threshold signal is a percentage of the difference between the PDAC signal and the NDAC signal.