Abstract: A strain relief device for protecting a power cord includes a tubular base member defining a lumen adapted to accommodate a power cord. The lumen includes a trailing lumen, a leading lumen, and an annular recess formed between the trailing and leading lumens. The leading lumen has flat, tapered sidewalls. A tapered cylindrical plug is sized to snugly fit within the leading lumen and has a protruding annular rim at its narrow end. The diameter of the protruding annular rim is about equal to the diameter of the annular recess so that the rim snaps into the recess when the plug is inserted into the leading lumen. The plug is disposed in encircling relation to the power cord prior to insertion of the plug. Pulling on the power cord increases the compression of the plug about the cord due to the common taper of the plug and the leading lumen.

Abstract: A portable, battery-operated AC electromagnetic yoke for detecting surface defects in ferrous materials by employing an AC magnetic field. The yoke includes a circuit that produces a quasi AC square wave voltage. The resulting AC magnetic field is the required inspection method of common practice and is capable of demagnetizing upon completion of inspection. A first bank of batteries supplies approximately sixty volts positive DC and a second bank of batteries supplies approximately sixty volts negative DC to power transistors that are in electrical communication with the yoke. Logic circuitry is employed to switch the respective banks of batteries on and off to simulate an AC circuit. The logic circuit includes a clock for generating pulses that are fed to a phase splitter circuit and to a delay and pulse shaping circuit. The respective outputs of those circuits are fed to logic gates that are in electrical communication with a voltage level shifting circuit that triggers the power drivers.