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.
The transient potential drop method is based on measurement of the transient voltage on the surface of a conductor due to the injection of a pulsed current. In this paper, we consider an approximate analytical model for four-point transient potential drop measurements on plates that are thin compared to the probe separation. Experimental results show good agreement with the theory for measurements made on non-magnetic and ferromagnetic plates when an exponentially rising pulsed current is used as a source. To demonstrate possible applications of the theory we consider measurement of the conductivity and relative permeability of the materials as well as plate thickness.
A common problem encountered in recording delayed light emission is that the signal of interest is preceded by a much more intense signal arising from prompt fluorescence. When a photomultiplier tube (PMT) is used as the photosensor in a pulsed-source phosphorimeter, two options are open to an experimenter who finds mechanical shutters inconvenient or impracticable and photon counting inappropriate: apply an electronic gate that suppresses the PMT gain for a brief period, or use a wiring scheme that enables the PMT to quickly regain normal operation after an intense burst of prompt emission. The performance of a squirrel-cage PMT that operates in the latter mode is compared with a new gateable PMT (Hamamatsu H11526 series) with a minimum gate time of 100 ns. The two detectors are found to provide practically the same temporal record of the delayed emission, but the ungated PMT is slightly superior in terms of recovery time and signal-to-noise ratio.
We have compared transient potential drop measurements on ferromagnetic steel rods with finite difference simulation assuming that the magnetization varies as a quadratic function of the applied field. Good agreement between simulation and experimental measurement is achieved and the results are discussed in terms of the Rayleigh law of magnetization.
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