A Wide frequency range circuit for measuring mutual capacitance with application to monitoring of metal fill profile

Abstract

Lost foam casting (LFC) is one of the most important casting methods in the production of complex castings. The metal-fill profile plays an important role in the casting quality and hence monitoring that profile is important to quickly discover failures in the process. A monitoring process based on electrical capacitive tomography (ECT) is developed by the research team. In ECT an array of capacitance measuring circuits is used to measure the mutual capacitance between the electrodes mounted around a target area. This paper presents a new high resolution capacitance measuring circuit with wide bandwidth developed to measure the inter-electrode capacitance changes produced as the grounded molten metal progresses within the target area. The developed circuit minimizes the effect of the stray capacitance while increasing the range of frequencies at which the circuit can be operated. This is particularly important to allow multiple circuits to operate simultaneously at different frequencies within the same flask. An illustrative example for use of tomography to monitor metal fill is presented.