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17 Jun 2002
Under a cooperative research and development agreement, NIST and the Aluminum Association have devised an eddy current probe that can operate in the harsh rolling mill environment and take a sheet's temperature without making contact with the metal. During the processing of all commercial metals, an accurate knowledge of the processing temperature is critical to achieving the final product's desired properties. This is particularly true during the rolling of sheet aluminum where temperature can influence formability, surface appearance and mechanical strength.
The aluminum sheet itself serves as the basic element of a resistance thermometer. The temperature is deduced from the relationship between electrical resistivity and temperature. A standard deviation of plus-or-minus 3 degrees Celsius was achieved for exit temperatures (the temperature of the sheet as it leaves the rolling stand and is coiled for cooling and shipment).
The eddy current technique achieved accuracies approaching those of contact thermocouples applied to processed metal held stationary at the exit stand of the rolling mill.
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