Image Number 5 for United States Patent #4380734.
The magnetic intensity in a succession of strips (12) in an article (10) is measured by producing relative motion between the article (10) and a magnetic sensing head (23) to produce a succession of first voltage waveforms. Each such waveform has a shape substantially characterized by the positions of the poles (13 and 14) in a respective strip (12). Each incremental portion of the shape has an amplitude proportional to the magnetic intensity sensed along the surface of the strip (12) and to the instantaneous speed of the relative motion between the sensing head (23) and such surface. By coupling a generator (31) to the article (10), a second voltage waveform is produced having a shape for each strip, wherein each incremental portion has an amplitude proportional to an instantaneous speed equivalent to the speed producing the first voltage waveform for the respective strip (12). The first waveform of a strip (12) is fed into the numerator input "Z" of a dividing circuit (36) and, simultaneously therewith, the second waveform for the same strip (12) is fed into the denominator input "X1" of the same circuit (36). Advantageously, the circuit (36) has a processing speed sufficient to produce a third voltage waveform of a shape wherein each incremental portion is independent of the speed of the relative motion and is faithful in amplitude and position to the poles (13 and 14) in each respective strip (12).