Importance

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Abstract

Apparatus (40) locates welds or other junctures (20) in sheet material (12). The apparatus (40) includes a sensor (16) that produces a varying signal that is a function of the distance (100) between a surface (26) of sheet material (12) and the sensor (16), a differentiator circuit (42) differentiates the varying signal as a function of time, a comparator (44) compares the differentiated signal with a calculated allowable and sends a signal to an input (90) of an electronic latch (46), the electronic latch (46) sends a signal to a reject mechanism (48), and the reject mechanism (48) sends a reject-accomplished signal to a reset terminal (98) of the electronic latch (46). The method of the invention includes transporting the sheet material (12), producing a rate of change signal that is a function of changes in thickness (18) of the sheet material (12), determining an allowable rate of change signal, and comparing the produced rate of change signal with the allowable rate of change signal. Preferably, the producing step includes obtaining a varying electrical signal whose variations are a function of variations in the thickness (18) of the sheet material (12), and developing a rate of change of signal from the varying electrical signal.

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First Claim