Measuring the diameter of a metal product during manufacturing is an important Quality Control activity in many industries including manufacturing of wires, nails, metal tubes and many more. Using manual measuring techniques in such situations is impractical because it is slow and time consuming. Many attempts have been made to automate the monitoring of the diameter of manufactured wires without disruption to the manufacturing process but these systems are either complicated to set-up or very expensive. This paper investigates the feasibility of measuring the diameter of a conductive material with circular cross section area (e.g., wires, rods, nails, etc) without making any physical contact with the material itself. Such a measuring system could be extremely useful as a Quality Control mechanism for monitoring the fluctuations in the diameter of manufactured wires, rods or nails without disrupting the manufacturing process. The experimental activity has involved the design, construction and testing of a prototype system to measure the diameter of different metals, both solid bars and hollow tubes, without making physical contact with the samples. The theory of operation of the proposed system is based on the well-developed Contactless Resistivity Measurement theory used in Solid State Physics where the main interest is to measure the resistivity of the material knowing its dimension. In this project, we are trying to investigate the feasibility of using the same principle to measure the dimension of the sample knowing its resistivity. Results presented in this project proved the possibility of measuring the diameter of a conductive material without making physical contact with it. The system operates by applying high current pulses to the excitation (primary) coil. These pulses will create a pulsating magnetic field, which in turn, causes eddy currents to flow in the sample. The field of these currents is picked by a pick-up coil placed too close but not in contact with the sample. The signal from the pick-up coil is then processed to extract the diameter of the sample. Results proved the feasibility of using this principle to measure fluctuations in the outer diameter of metal bars and tubes.
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