Pulse eddy current testing apparatus using pulses having a 50% duty cycle and precise quadrature gates

TLDR: In this paper, a sine wave oscillator feeds a square wave generator, and the generator produces 50 percent duty cycle pulses having leading and trailing edges coinciding with alternate edges of the square wave.

Abstract: A sine wave oscillator feeds a square wave generator. Pulse generator means produces 50 percent duty cycle pulses having leading and trailing edges coinciding with alternate edges of the square wave and 25 percent duty cycle pulses having leading and trailing edges coinciding with successive edges of the square wave. Gate generating means produces one series of gating pulses coinciding with the leading or trailing edges of the 50 percent duty cycle pulses and a second series coinciding with edges of the 25 percent duty cycle pulses lying halfway between the edges of the 50 percent duty cycle pulses or halfway between successive pulses. The 50 percent duty cycle pulses drive test coil means whose output is supplied to an amplifier tuned to the PRF thereof, and then to a pair of quadrature detectors supplied with respective series of gating pulses.