| 摘要 |
<p>EDDY CURRENT TESTER An Eddy Current Tester for Detecting defects in conductive materials employs phase rotation curcuitry for eliminating the effects of lift-off signals from the reactive component of the output of an eddy current probe. An operator digitally selects a frequency which is input to the eddy current probe which is adjacent a test material. The signal output from the eddy current probe is amplified and demodulated into reactive and resistive components which are processed by phase rotation circuitry. The phase rotation circuitry is calibrated by applying a lift-off signal thereto while a phase adjust switch is on. When the phase adjust switch is on the reactive signal component is applied to a zero crossing detector which in conjunction with a flip flop controls the counting direction of an counter which addresses a sine-cosine table in a erasable programmable read only memory. The sign-co-sine values are strobed into a latch which provides the sine-cosine information to multiplying curcuits which multiply the reactive and resistive signal components output of the demodulator by the sine and cosine stored in the latch. The outputs of the multiplying curcuit are input to a phase rotator which outputs signals which are rotated in the complex plane by the angle corresponding to the sine and cosine stored in the latch. While the phase adjust switch is on, the reactive component of the output of the phase rotator hunts about zero. When the phase adjust switch is off, the phase rotator rotates the phase of any signal input into the multiplying circuitry by the angle indicated by the last sine and cosine values strobed into the latch.</p> |
