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 magnetic field sensor signal having an amplitude proportional to an ambient magnetic field and having a gain; an automatic gain control circuit coupled to the magnetic field sensor and configured to receive the magnetic field sensor signal, the automatic gain control circuit configured to adjust the gain of the magnetic field sensor signal by an adjustment amount dependent on the amplitude of the magnetic field sensor signal to provide a gain-controlled version of the magnetic field sensor signal and to generate an output indicative of the adjustment amount; and a True Power On State detector comprising: means for generating a threshold signal; and a comparator having a first input coupled to the magnetic field sensor to receive the magnetic field sensor signal or the gain-controlled version of the magnetic field sensor signal, a second input coupled to the threshold signal generating means for receiving the threshold signal, and a comparator output, the comparator configured to compare the magnetic field sensor signal or the gain-controlled version of the magnetic field sensor signal with the threshold signal and to generate and provide at the comparator output the magnetic article detector output signal, the magnetic article detector output signal being indicative of whether the magnetic field sensor signal or the gain-controlled version of the magnetic field sensor signal exceeds the threshold signal, wherein the True Power On State detector is coupled to the automatic gain control circuit such that the True Power On State detector receives the output indicative of the adjustment amount, and wherein the True Power On State detector is configured to adjust the threshold signal in increments having a size that is a function of the adjustment amount. a magnetic field sensor providing a magnetic field sensor signal having an amplitude proportional to an ambient magnetic field and having a gain; an automatic gain control circuit coupled to the magnetic field sensor and configured to receive the magnetic field sensor signal, the automatic gain control circuit configured to adjust the gain of the magnetic field sensor signal by an adjustment amount dependent on the amplitude of the magnetic field sensor signal to provide a gain-controlled version of the magnetic field sensor signal and to generate an output indicative of the adjustment amount; and a True Power On State detector comprising: means for generating a threshold signal; and a comparator having a first input coupled to the magnetic field sensor to receive the magnetic field sensor signal or the gain-controlled version of the magnetic field sensor signal, a second input coupled to the threshold signal generating means for receiving the threshold signal, and a comparator output, the comparator configured to compare the magnetic field sensor signal or the gain-controlled version of the magnetic field sensor signal with the threshold signal and to generate and provide at the comparator output the magnetic article detector output signal, the magnetic article detector output signal being indicative of whether the magnetic field sensor signal or the gain-controlled version of the magnetic field sensor signal exceeds the threshold signal, means for generating a threshold signal; and a comparator having a first input coupled to the magnetic field sensor to receive the magnetic field sensor signal or the gain-controlled version of the magnetic field sensor signal, a second input coupled to the threshold signal generating means for receiving the threshold signal, and a comparator output, the comparator configured to compare the magnetic field sensor signal or the gain-controlled version of the magnetic field sensor signal with the threshold signal and to generate and provide at the comparator output the magnetic article detector output signal, the magnetic article detector output signal being indicative of whether the magnetic field sensor signal or the gain-controlled version of the magnetic field sensor signal exceeds the threshold signal, wherein the True Power On State detector is coupled to the automatic gain control circuit such that the True Power On State detector receives the output indicative of the adjustment amount, and wherein the True Power On State detector is configured to adjust the threshold signal in increments having a size that is a function of the adjustment amount.