| 摘要 |
<p>An oval-shaped sensor is used to measure the material content of the outer ring of a bicolour coin, the coil being mounted on a ferrite whose inner portion has a diameter which is wider than the inner disc of the bicolour coin so that eddy currents are confined to the outer ring. A thickness sensor may be mounted within the oval sensor, and a separate coil is used for measuring the material content of the inner disc. The thickness sensor may also be used for measuring material down to a different depth, for validating clad coins. The oval sensor is used also for diameter measurement.
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