Detection of passing magnetic articles with a peak-to-peak percentage threshold detector having a forcing circuit and automatic gain control

A method for starting a proximity detector including a magnetic-field-to-voltage transducer which provides a signal voltage, Vsig to a peak-to-peak percentage threshold detector which includes first and second tracking circuits and a threshold comparator and which generates an output signal voltage Vout, the method comprising the steps of:

• (a) setting an output value of the first tracking circuit to a value which is lower than the least positive expected value of the signal voltage Vsig wherein the first tracking circuit receives the signal voltage Vsig, and generates at an output port thereof a voltage PDAC, that tracks the highest peak of the signal voltage Vsig;
• (b) setting an output value of the second tracking circuit to a value which is greater than the least negative expected value of the signal voltage Vsig wherein the second tracking circuit receives the signal voltage Vsig, and generates at an output port thereof a signal voltage NDAC, that tracks the lowest peak of the signal voltage Vsig;
• and
• (c) maintaining the output signal voltage Vout at a first predetermined value by applying a reference voltage to an input terminal of the threshold comparator, wherein the value of the output signal voltage Vout is maintained at least until the peak-to-peak percentage threshold detector detects a change in the signal voltage Vsig which is greater than a predetermined voltage.

A proximity detector for sensing magnetic articles comprising:

• (a) a magnetic-field-to-voltage transducer for generating at an output port thereof a signal;
• (b) an automatic gain control circuit having an input port coupled to the output port of said magnetic-field-to-voltage transducer and having an output port, said automatic gain control circuit for controlling the amplitude of a signal voltage Vsig, that is proportional to a magnetic field;
• (c) a peak-to-peak percentage threshold detector having an input port coupled to the output port of said automatic gain control circuit to receive the signal voltage Vsig and for providing an output signal voltage Vout;
• and
• (d) a circuit coupled to said automatic gain control circuit and said peak-to-peak percentage threshold detector for maintaining the value of the output signal voltage Vout at a first predetermined value to prevent said peak-to-peak percentage threshold detector from switching prior to one of a positive or negative excursion of the signal voltage Vsig reaching a predetermined threshold voltage when said automatic gain control circuit controls the amplitude of the signal voltage Vsig.

A method for operating a proximity detector including a magnetic-field-to-voltage transducer coupled to an automatic gain control circuit which provides a signal voltage Vsig to a peak-to-peak percentage threshold detector which includes first and second tracking circuits and a threshold comparator and which generates an output signal voltage Vout, the method comprising the steps of:

• (a) setting an output value of the first tracking circuit to a value which is lower than the least positive expected value of the signal voltage Vsig wherein the first tracking circuit receives the signal voltage Vsig, and generates at an output port thereof a voltage PDAC, that tracks the highest peak of the signal voltage Vsig;
• (b) setting an output value of the second tracking circuit to a value which is greater than the least negative expected value of the signal voltage Vsig wherein the second tracking circuit receives the signal voltage Vsig, and generates at an output port thereof a voltage NDAC, that tracks the lowest peak of the signal voltage Vsig;
• (c) maintaining a value of the output signal voltage Vout at a first predetermined value by applying a reference voltage to an input terminal of the threshold comparator, wherein the value is maintained at least until the peak-to-peak percentage threshold detector detects a change in the signal voltage Vsig which is greater than a predetermined voltage.