Fibre-optic solution

North Otago Irrigation Company has recently completed the Downlands Scheme irrigation project. The project, which was designed to take water from the Waitaki River and irrigate up to 10,000 hectares of dry farmland in the Black Point, Enfield and Napara areas near Oamar, was constructed over 18 months and commissioned last Spring.

During the planning stages, the senior electrical and control systems engineer from Beca Infrastructure Ltd contacted Lloyd Bennett, the data and communications specialist from the Corys Electrical and MasterTrade group of companies, to discuss the best fibre-optic backbone options required to link the seven pump stations together.

With this in mind, a singlemode fibre-optic backbone was recommended due to the distance between pump stations. This also provides for the additional bandwidth in the network if the scheme is expanded in the future.

MasterTrade Oamaru looked after the main requirements of the project. Andrew Hobson, the branch manager, and his team coordinated the logistical requirements of getting 10,200 m of fibre-optic cable to the site, as well the large quantities of duct pipe and associated product. They also supplied the fusion-splicing equipment and accessories to the project engineers, Delta Utility Services from Dunedin.

Industrial Controls South Canterbury Ltd carried out the secondary works of commissioning of the network, which included the OTDR testing of the fibre-optic backbone.

The EOTec 2000 range of Weed Instruments Fiber Optic Modems was chosen for the Downlands Irrigation Project fibre-optic backbone structure. Two fibre backbones were configured for the project. One backbone provides a Modbus Fibre network and the second backbone facilitates ethernet fibre network between the various pump stations.

The Modbus fibre backbone is configured in a self-healing ring mode, which gives fibre media redundancy in case 'the loop' is broken. Data will always be routed on the shortest possible path to reduce propagation delay through the system.

Most process plants and factories have unique requirements for communication networks that differ from those of a commercial network. Industrial network components must withstand harsher environmental conditions such as extreme temperature ranges, lightning strikes, electromagnetic interference and hazardous locations.

Mounting and spacing requirements are also an issue, since industrial networking components must be mounted in the same control panel with other control equipment. The modular EOTec brand of industrially hardened fibre-optic communication products addresses these issues and provides solutions for factory automation and process control. Temperature specs are between -40 and +85°C.

Features include ethernet connectivity with a 4-port switch, compatibility with major PLC brands, and multimode and singlemode fibre-optic interface modules. Using the easy-to-install, lightweight modules, all major network topologies can be configured including Star and Self-Healing Ring. A hot-swappable dual power supply option with diagnostic outputs eliminates a single point of failure.

In addition, a variety of DIN rail-mounted industrial ethernet switches and media converters is part of this range of products. Multi-channel contact closure modules allow analogs, digitals and RS232 signals to be transferred over a single fibre, giving immunity against electrical noise (EMI/RFI).

The cost of fibre-optic cable and its associated connectors and hardware has decreased steadily over the years. Today, the benefits of fibre-optics can far outweigh the costs, making fibre-optic communications the preferred choice for industrial factory automation and process control networks.

These fibre-optic modems have been approved under Rockwell Automation's Encompass program, GE-Fanuc's Accompany program and Schneider's Alliance program.

Supported Electrical Interfaces/Protocols are: ethernet, Allen-Bradley DH+, Allen-Bradley DH485, ControlNet, DeviceNet, Modicon Modbus +, Modicon Remote I/O, GE-Fanuc Genius, RS232/485 and Profibus.