Note that the present disclosure is described in terms of a preferred embodiment of the invention for use with eddy current probes. However, the applicability of the invention is not limited to eddy current probes, and all applications of the invention to other types of non-destructive inspection probes, such as ultrasonic probes, are within the scope of the present disclosure.
Eddy Current (EC) is a commonly used method for non-destructive testing and inspection (NDT/NDI). Single-coil probes use a single EC sensor for inspection, whereas Eddy Current Array (ECA) probes use multiple sensors in order to increase the inspection coverage. Using multiple excitation coils and receiving coils (sensors) allows the user to inspect a given surface faster than with a single EC sensor. Array probes using up to 32 sensors are not uncommon.
An important aspect of NDT/NDI with EC probes is management of the noise in the EC signal. In absolute single-coil probes, generator noise coming in on the same line as the much weaker EC receiver signal is a limiting factor. Differential probes permit the receiver to reject most of the excitation signal and consequently differential EC probes are often preferred, even though differential probes, having two coils instead of one, are less compact and more costly than absolute probes. Reducing the generator noise would increase the signal-to-noise ratio (SNR) of absolute probes, making these probes usable in applications where only differential probes could be used before. Alternatively, less power could be used to drive the probes, while obtaining the same SNR as before the generator noise reduction.
For differential probes, generator noise is less of a problem, however some generator noise bleeds through because of probe imbalance or imperfect common-mode rejection of the differential amplifier. Therefore improvement of the SNR would be beneficial also for differential probes.
The same advantages of noise reduction apply both to single EC probes and to ECA coil arrays. Likewise, noise reduction is advantageous for all other types of NDT probes.
Therefore, there exists a need in existing practice for reduction of noise and increase of SNR for NDT/NDI.