Method for monitoring the integrity of an eddy current inspection channel

#The present invention relates to non-destructive testing and inspection systems (NDT/NDI) and, more particularly, to Eddy Current (EC) or Eddy Current Array technology (ECA), employing eddy current probes with a test loop linked to it, which allows checking the integrity of the testing system.

#Eddy current inspection is commonly used as a non-destructive method to detect flaws in surfaces of manufactured components fabricated from a conductive material, such as bars, tubes, and special parts for automotive, aeronautic or energy industries.

#Typical eddy current sensor configurations are impedance bridge, pitch-catch (alternatively called reflection or transmit-receive) and differential, but can also include more complex combinations such as pitch-catch with differential receivers, multi-differential, etc.

#FIG. 1 shows the test loop for a simple configuration of one channel composed of one coil.

#FIG. 2 illustrates the impedance plane signal associated with the activation of the test loop. This figure shows the reference test loop signal (operation point shift vector) as well as the signal associated with the current probe check evaluation.

#FIG. 3A shows the test loop for a pitch-catch coil configuration. Each transmitter or receiver is composed of a channel. Each channel can be composed of a different coil number and configuration.

#The test loop of the present invention is based on eddy current basics. Thus, when a shielding loop is positioned around an eddy current test coil, a signal will be induced in the loop and this signal will change the magnitude and phase of current flowing in the coil. The detection of these changes enables checking the ECA inspection system functionality.

#FIG. 1 is a simple configuration of the test loop in one channel, which is composed of a single coil 1, which is being used for both the generation and reception of the eddy current signals. The test loop 3 in this case consists of a conductive circuit, which turns around the inspection coil 1. The switch 5 is utilized to activate test loop 3. Once the switch 5 is closed, an eddy current is induced in the test loop 3. Consequently, the coil 1 impedance is changed. However, when the coil 1 is broken, it does not induce current in test loop 3 and consequently, shows no changes in coil's 1 impedance associated with the switch 5 position.

#The electrical impedance (Z) is the total resistance that a circuit presents to an alternating current. In Eddy current circuits, impedance includes the possible resistance (R) and the inductive reactance (XL) components. The resistance component and the reactance component are not in phase, so vector addition must be used to relate them to the overall impedance. For an eddy current circuit with resistance and inductive reactance components, the total impedance is calculated using Z=√{square root over (R2+XL2)}.