Evaluation of four-point transient potential drop on conductive plates

Abstract

We have derived an analytical solution for the transient potential drop due to a step function excitation of a four-point probe on a conducting plate. Similar expressions have already been developed based on a previous analysis for a conducting half-space. The purpose of this article, however, is to extend the theory to measurements on conductors of arbitrary thickness and thereby broaden the practical applicability of the technique. The results are useful for non-destructive measurements of the conductivity, permeability and wall thickness of metals. Further applications of the technique include monitoring material loss due to corrosion and measurement of factors that affect the electromagnetic properties of materials such as mechanical stress.

Potential difference methods for measuring crack growth: A review

“…Compared with the whole body affected in DCPD, in ACPD the current field concentrates in a narrower layer near the material surface, thus a lower excitation current is sufficient to supply easily measurable potentials [10,13,29,40,41,74,76,84,96,124,125,127,131,137,139], thereby minimising the risk of localised heating [13,96,139]. Hence, ACPD is able to achieve higher sensitivity than DCPD, especially for small crack lengths near the surface of materials [13,34,40,41,132,141] and the effect of specimen geometries is reduced [13]. Verpoest et al [132] have applied high frequency ACPD to detect and monitor surface cracks in un-notched steel rods and gave the conclusions that a 40 current frequency would allow detection of cracks in an area of 0.05% of the specimen cross-section, which was unachievable by the other NDT techniques.…”

“…where and are of magnetic permeability and electrical conductivity, respectively, and is the AC frequency. Hence by applying multi-frequency AC in ACPD tests, specific inspection can be conducted in different depths of the specimen [10,84,141,145]. Conversely, in cases of deep cracks and crack tunneling, particular attention should be paid to ensure the AC covers the whole inspection region [20,40].…”

Modeling of Non-Linear and Hysteretic Magnetization Effects in Transient Potential Drop Measurements

“…Here we consider the transient potential drop method [3,4] where, by using a pulsed current as the source, sensitivity to varying depths is achieved rapidly and by experimentally simple means. Due to the skin effect the variation of material properties and geometrical features with depth is manifested as a time dependent variation in the transient potential drop analogously to the frequency dependence in alternating current potential drop (ACPD) [5].…”

Four-point transient potential drop measurements on metal plates

“…Early work on transient PD was made by Hognestad and Honne [11] for measurement of tensile and compressive stresses in steel rods. More recently, theoretical evaluations were given for four-point transient PD measurements on planar half-space conductors [12] and plates [13] based on inverting the corresponding frequency-domain (ACPD) results [2]. However, these predictions have so far not been compared with experimental measurements to validate the theory and demonstrate its practical use.…”

“…Although the existing literature on ACPD theory and experiment lends confidence to the validity of transient measurements, the latter requires in general that the time-dependence of the drive current is taken into account whereas in ACPD a simplification is made where the current is assumed to be sinusoidal with a given frequency. An analysis assuming a finite rise time of the drive current was given in [12] for transient four-point measurements on a half-space, but the analysis for plates in [13] was limited to the simplest case of an ideal step current.…”