February 2020

55 www.drivesncontrols.com February 2020 SENSORS n Long-distance sensors ensure that car audio knobs have their washers T he plastic knobs used to control car audio systems are held in position by small spring washers that are fitted to each knob after moulding. A Portuguese manufacturer of these knobs transports them to automotive plants in transit trays, each containing 70 knobs. Occasionally, the washers are omitted or become dislodged, resulting in car-makers rejecting entire batches of knobs. Manual inspection of each knob is neither practical nor cost-effective, so the knob manufacturer has designed a custom-built testing machine to check whether the washers are present and in the correct position. This machine required sensors that could test each knob in-situ in the transit tray. The manufacturer decided to use long-distance inductive sensors for this role. The size and position of the washers made the task particularly demanding. Each 10mm- diameter washer is formed from 1mm-diameter steel wire. These are located at 45mm centres in the transit trays, with the washers lyingmore than 10mm above the sensors. The sensors had to be able to operate reliably in close proximity to each other, sensing the presence of the washers through the plastic tray. The plastics manufacturer chose Contrinex’s M18-diameter Extra Distance inductive sensors for the application. These are designed to operate reliably at sensing distances of up to 12mm. They allow a minimum clearance between sensors of only 44mm, thus accommodating the required spacing. A bank of 70 sensors, mounted in a custom-built testing fixture, aligns precisely with the positions of the knobs in the transit tray above. Locating lugs position the tray correctly, while clamps secure it during the testing cycle. It takes only a few seconds to check for the presence of a washer in each of the 70 knobs in the tray. If a washer is missing, the position of the faulty knob is identified immediately. The M12 connectors allow individual sensors to be removed and replaced easily for maintenance. n A Portuguese plastics manufacturer is using long-distance inductive sensors to check the presence of vital washers in control knobs destined for car audio systems. Long-distance inductive sensors confirm the presence of a washer in each assembly

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