| 摘要 |
<p>Method and device for phase-selective testing and/or measuring of test objects, such as hot steel billets, with eddy current techniques with respect to surface cracks or other magnitudes, whereby at least one signal, e.g. A sin omega t, derived from this magnitude is detected by means of at least one phase-sensitive detector The output signal from an ordinary phase-controlled rectifier can be substantially described via, e.g. sin alpha and/or cos alpha functions in which alpha indicates the phase position of the control signal in relation to the input signal. By e.g. multiplying sin alpha by cos alpha , sin 2 alpha or cos 2 alpha functions are obtained which in turn can be multiplied to obtain the function sin 4 alpha corresponding to narrow sensitivity lobes in the transducer's impedance plane, thus permitting effective separation of the various types of vector. The invention thus provides an improved conventional phase-sensitive detector, making it more phase-selective by adding at least one product and/or one quotient former.</p> |
