Linear encoder is adequately sealed for measuring fish

When Terralogic Ltd, a provider of rugged computers, wanted to source a linear encoder that could work in harsh outdoor conditions, the Cardiff-based company turned to the SHG-TT from Newall Measurement Systems. Now, with a handful of rigs having undergone successful prototype evaluation by the customer, UK and worldwide roll-out looks almost certain to follow.

As part of the fisheries management programme, the Environment Agency, the public body responsible for protecting and improving the environment in England and Wales, wanted to improve its methods of fish measurement; the agency had previously been using conventional notebook logging methods for monitoring fish size within inland waterways.

"The Environment Agency approached us to provide an integrated method of recording fish measurement data," explains Terralogic's Managing Director, Ken Gray. "Their existing methods were both time-consuming and open to misinterpretation."

Terralogic recommended one of its 'rugged' tablet computers to allow the agency to undertake live data capture in the field and therefore improve the lead-time and accuracy of its fish surveys. However, one dilemma confronting Terralogic was the necessity for a linear encoder with the ability to perform accurately and repeatedly in wet outdoor conditions. "We trawled the internet and caught sight of the SHG-TT from Newall," says Mr Gray. "Having checked out its specification we thought it was right for the application."

Encoders sealed to IP67

The latest SHG linear encoders are claimed to be unique in that none of the electrical or measuring components are exposed to harsh environments, and they will continue to provide accurate and reliable readings even when fully submerged in water or oil. For this reason the entire range carries an IP67 (NEMA 6) environmental rating.

These solid-state devices use digital signal processors and high-speed analogue-to-digital converters to provide rapid, accurate and repeatable positioning information. Newall SHG-TT linear encoders offer differential quadrature output at RS422 TTL levels. The units are modular and available in lengths of up to 30m.

"We did look at other makes and models of linear encoder," explains Mr Gray, "but the accuracy and waterproof functionality of the Newall unit made up our minds."

Having acquired its first SHG-TT, Terralogic set about incorporating the unit into the custom-designed fish measuring rig controlled by the company's rugged computer. A trough is used to cradle the fish while a bar is moved manually to measure its length. A single button-push on the tablet computer's touchscreen is all that is required to record its length. A Deva interface is used to link the SHG-TT linear encoder with Terralogic's rugged computer.

Working evaluation

Eight prototype rigs have now been supplied to the Environment Agency, which is currently performing a working evaluation of the product. Once the rig gets the final approval, Terralogic anticipates an extensive delivery programme incorporating the UK and the rest of the world.

Formed in 2000, Terralogic has become a UK leader in the provision of rugged computer-based systems (laptops, tablets, PDAs) that are shock-, water-, and dust-resistant. These meet or exceed MIL-STD-810E, 810F and IEC-68-2 environmental specifications. The company's international client base includes telecom engineers, geo-survey companies, the armed forces, the emergency services and civil aviation organisations. Terralogic's entire range is based on military and marine-grade environmental performance standards. Communications requirements from MESH networks to Tetra, wireless LAN and GPRS can be satisfied.