Test & measurement
winding. Proportional to the magnitude of the force, this alternating voltage is converted into a DC voltage that is conveyed in modern applications as a 4-20 mA or digital signal to a programmable logic control (PLC) system. In contrast with conventional strain gauges, electrical signals produced by the sensor are not dependent on any kind of physical movement. Combining exceptional sensitivity and measurement accuracy with an impressive tolerance to overloads, the transducer also produces high DC output signals that are resistant to electrical interference.
A NEW BENCHMARK FOR QUALITY, CONSISTENCY AND RELIABILITY Following a successful Swedish patent application by Dahle in 1953 – and a subsequent US filing the following year – Pressductor made its first commercial appearance in a roll force metering system delivered in 1954 to Surahammars Bruk, a Swedish producer of electrical steel for use in transformer cores. The new system allowed the 0.5mm sheets to be rolled with a more even reduction in thickness, achieving an optimal magnetic structure and greater electrical efficiency by reducing unwanted air gaps when the steel plates forming the transformer core were sandwiched together.
Over the next few years, the technology was
rapidly embraced by the metals industry. With annual global steel production in 1954 – then around 200 million tonnes – set to triple over the next fifteen years, Pressductor’s advent was timely. Its commercial success was also to lead directly to another innovation, based on the same principle of steel’s magnetic permeability changing when an external force is applied.
During the 1960s, demand was steadily increasing in the metals industry for a measurement solution to improve control of flatness in rolled steel, aluminium, copper and bronze products. While automatic gauge control with the help of Pressductor had allowed improvement in sheet and strip thickness tolerances, maintaining consistent strip flatness remained a persistent challenge for rolling mill operators.
In 1967 Pressductor sensing technology was incorporated in the world’s first flatness measurement system delivered to Alcan Industries. The Canadian producer had struggled with rolling sheet aluminium to the desired flatness and quality, demanding a reduction in rolling speed as well as a narrower rolling width that severely compromised production yields. Subsequently christened Stressometer, the sensor roll installed at the mill’s exit provided an elegant solution to true parallel differential force measurement across the entire width of the aluminium strip. Rapid refinements to the prototype system allowed Alcan
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