Motion System Design
Linear position sensor aids Alaskan fisheries

Linear position sensor aids Alaskan fisheries

Rick Towler of the National Oceanic and Atmospheric Administration needed help in solving an equipment challenge, which drove him to contact application engineers at MTS Systems Corp. Sensors Division, Cary, N.C. As part of the National Marine Fisheries Service, Towler needed an accurate and durable method for measuring fish in the waters around Alaska, but one less expensive than the $20,000 commercially available systems.

Initially, MTS sold Towler a single sensor — an off-the-shelf non-contact EP2 series sensor with nonlinearity of less than 0.03% and repeatability within 0.005%. Towler explains that accurate fish-length estimates are needed to determine biomass and properly set commercial fishing limits. “Accuracy is important because in the end, it comes down to people's jobs,” he says.

Towler and his colleagues had been using a barcode reading wand and laminated piece of paper marked with barcodes for different lengths. The team laid individual fish on the paper and then scanned the corresponding barcode to record the animal's length. However, this method only allowed centimeter accuracy, and the wands and laminated charts were too fragile for the cold, wet, and salty environment.

In contrast, Towler's new fishboard is plenty robust for Alaskan conditions. It fully integrates the EP2 and a small circuit board; the user simply waves a magnetic finger sleeve past the appropriate board location to record fish length. The new fishboard can also measure down to millimeters. Towler says that because the sensors are fast and accurate, they have helped to streamline the fish measurement process. In fact, the government-designed fishboard tool is now available to everyone, and costs only a fraction of the commercially produced fish-measuring devices. For more information, visit

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