An Electronic Eddy Current Sensing Circuit U.S. Patent 3,609,580 Figure 5, sheet 2 of 2
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						The schematic at left presents Figure 5 of U.S. Patent 3,609,580.  The circuit is a three transistor oscillator circuit that is designed to detect eddy currents caused by a cold rolled steel pole piece that is inserted in the ID of the oscillator coil shown as item 14.
		The coil inductor located in the top left side of this picture and shown as a 176 uH inductor in the schematic can be designed to generate a voltage at the output of the circuit indicating a linear travel position movement or point.  The coil in this picture will generate a linear travel position indication of .5 to 4.5 Volts which represents a linear position travel  from 0 to .75 Inches when one inserts a round cold rolled steel core into the coil ID.