FOERFARANDE FOER ATT UTFOERA ICKE-DESTRUKTIV KONTROLL MED TILLHJAELP AV VIRVELSTROEMMAR OCH HAERFOER LAEMPAD ANORDNING DAER MAN ANVAENDER EN FLERFREKVENT MAGNETISERING OCH MED VARS HJAELP MAN KAN ELIMINERA VISSA PARAMETRAR

摘要

1521203 Eddy current testing COMMISSARIAT A L'ENERGIE ATOMIQUE 8 Sept 1976 [9 Sept 1975] 37174/76 Heading G1N The invention relates to a process and apparatus for eddy current testing of objects wherein a part of the initial signal produced in the process or apparatus is eliminated, the part being due to a parameter or parameters of the object. The process comprises the steps of displacing a probe 12 in the proximity of the object, supplying the probe with an excitation current of n different frequencies as from oscillators 26, 28 and analyzing the components of each of the n frequencies in the signal provided by the probe. The analysis comprises for each component separating the resistive part in phase with the excitation current from the reactive part Y in quadrature. Parts X, Y of a component at a first frequency are then modified so that in the overall signal the part of the signal corresponding to a parameter to be eliminated is coincident and equal to the part of the signal corresponding to the parameter of a second frequency. The modified signal and signal at the second frequency are then subtracted to provide a signal corresponding solely to a fault. The signal produced by the subtraction is displayed as on a CRT 90. As shown the probe 12 comprises a bridge network of two resistances 18 and two inductances 20 the output at 24 being fed through a circuit comprising a pre-amp 34 or imbalance compensating circuit 36, an amplifier 42, two band pass filters 44, 46 each centred on one of the two frequencies respectively, amplifiers 48, 50, analyzing memory circuits 52, 54 receiving reference signals from respective oscillators 26, 28 and low pass filters 68, 70 to provide the respective resistive and reactive parts X A , Y A , X B , Y B . The last mentioned parts pass to the elimination circuit which comprises for each frequency a weighting circuit 80, 82 whereby the signals may be partly modified as stated above as by the employment of multipliers 80x, 80y, 82x, 82y. The phase of the partly modified signals from circuit 80 is then phase shifted in a dephasing circuit 84 from where the signals are fed to subtraction circuits 86, 88. A circuit 92 is interposed between the subtraction circuits 86, 88 and the CRT 90 such that the orientation of the signal displayed thereon may be adjusted. Switching means 94 may be provided such that signals at various points of the circuit may be applied to the CRT 90.