Enhanced Tramp Metal Detection System
The fiber carding equipment in the host plant was unusually large and less than a year old. When a sheet metal screw entrained in the fiber passed through the card, the resulting damage caused a sharp reduction in production capacity and tens of thousands of dollars in repair costs. Technicians were rushed in from out-of-state and spent several days replacing the specialized carding wire.
It was only when the failure resulted in that catastrophic event that engineering and maintenance staff discovered the cause - the last-ditch protection provided by the card's tramp metal detector had failed electrically some time before the fatal moment. As delivered by the manufacturer, the detector correctly warned of the presence of even tiny amounts of metal in the fiber. There was, however, no way to tell the difference between a lack of metal and a loss of detection capability.
WHY designed a tri-state detection circuit which used a spare input to the machine's PLC, a few discrete components, and a brief program change to provide an alarm for lost continuity in the warning circuit. The circuit and algorithm (patent applied for) was implemented inexpensively with local technicians and parts from the inventory spares, and provided effective detection and alarm response for this critical and expensive piece of machinery.
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