Development of multiple frequency electromagnetic induction systems for steel flow visualization

This paper presents recent developments in the use of electromagnetic induction tomography (EMT) for steel flow visualization. Several aspects are reported. First, results are shown from an 8-coil, single-frequency, EMT system from tests using liquid steel. The results are consistent with video recordings of an exposed section of the steel flow passing through a submerged entry nozzle, in terms of flow size and position, providing a good representation of the steel flow profile changes during trials. The second part describes the development of a system with a C-shaped sensor, which is capable of being slotted in place for practical deployment as well as being rapidly removed during nozzle changes. The effects of reducing the number of coils in this configuration were also studied. Finally, the development of a multiple-frequency system for plant use is reported. The system is designed based on a commercial data acquisition board, which can provide three sinusoidal signals with target frequencies for excitation simultaneously. This paper describes the new hardware electronics and software. Experimental results show that the system is able to identify a variety of test samples. Instead of imaging the cross-section of the steel flow profiles, the current system is developed for checking signal levels at different operation frequencies, which are of more interest for industrial use. Nevertheless, the work demonstrates a significant step forward to develop a multiple-frequency EMT system for practical use in this industrial process application.