A Low-Cost Contactless Transducer for the Measurement of DC Currents Up to 13 kA for the Industry of Anodized Aluminum

Abstract

This paper is concerned with the development and the characterization of an ad hoc transducer for the contactless measurement of a high-intensity direct current (dc) for industrial applications. Specifically, the proposed transducer will be used to measure the oxidation process current in a continuous aluminum coil anodizing line (standard sulfuric acid anodizing). In this oxidation process, the current measurement is required to control the thickness of the obtained aluminum oxide, the most important parameter in determining the overall quality of the process. Starting from the features of the considered process, the transducer must measure, without contact, dc currents up to 13 kA in continuous aluminum strips, whose width and thickness can be up to 1600 and 5 mm, respectively; the mass of each coil can be greater than 4700 kg, and the length can be more than 800 m. The dc current is supplied by an ac/dc converter, but due to the features of the oxidation process, only a fraction of the supplied current flows in the aluminum strip and concurs to the oxidation process; the remaining current flows as a leakage current in the acid solution, creating undesired phenomena and energy losses. In this paper, we propose a low-cost current transducer, whose sensing element consists of an iron core equipped with two windings; the first excites the core, while the second is used to measure the variation in the magnetic saturation of the core due to the dc current to measure. The transducer output is conditioned by an electronic circuit that gives a continuous voltage proportional to the input current. A prototype of the proposed transducer has been designed and implemented; a series of characterization tests has been conducted, and the obtained results are discussed in this paper. The transducer is able to measure up to 13 kA, with an overall accuracy of 1.5% for currents over 11 kA.