Although geographically small, New Zealand is home to a surprising number of the world's Biggest, Largest and longest.A 55m tall blue glass clad monolith rising out of the Waikato Valley in New Zealands North Island houses one of these "NZ biggest" which is said to be the worlds largest whole milk powder plant.The massive new plant is part of Anchor Products' Te Rapa milk processing site-one of 10 across the country owned and operated by the manufacturing arm of New Zealands largest dairy manufacturer,The New Zealand Diary group.The result of a two -year,US$85 million expansion project,The new Te Rapa Dryer 5 milk powder plant is designed to accomodate projected growth in the North Island milk supply through to 2005
Commissioned in August 1999, the new dryer is huge, easily dwarfing the site's three existing dryers. Dryer 5 has a processing capacity of five million litres of whole milk per day and can produce up to 23 tonnes of milk powder per hour. Technology wise, Dryer 5 is leading edge; and is the first manufacturing plant in the southern hemisphere to adopt the ControlLogix integrated control platform on such a scale.
Ian Steele, Anchor Products' Engineering Services Division Manager describes Te Rapa's move to ControlLogix as strategic rather than bold. ControlLogix' data-communications and wide integration strengths, backed by Allen-Bradley's open-communication architecture, fits with the dairy giant's long-term control strategy. Central to this strategy is the application of predictive automation, based around technologies developed by Anchor's alliance partner, Pavilion Technologies of Austin, Texas.
Steele and his team have spent much of the past decade honing Anchor's automation and control network strategy. Predictive control strategy is a key element; an essentially feed-forward control technique based on elaborate computer process models. Building such models requires realtime operational data - lots of it - delivered via a fast-response, control platform. Anchor's automation architecture - a futuristic control system to optimise access and use of plant-floor data - was conceptualised by the company in 1990. Heading up the neural system is a powerful plant historian computer, the site independent routing and reporting processor (SIRRP). Via its onboard web server, SIRRP provides process data from all 10 plants to the Anchor management team. It also stores and develops the data archive needed for predictive control. In turn, SIRRP is supported by distributed plant-level data networks - the essence of the neural-based architecture.
The Dryer 5 control system practically realises the Anchor neural architecture. It comprises a total of 12 ControlLogix controllers, almost 3000 ControlLogix I/O points and 1640 DeviceNet nodes. These are widely distributed across the new plant's three operation sectors (the 'dry' end, the 'wet' end and powder handling) and three 'service' areas (refrigeration, water and wastewater). Plantwide Ethernet and ControlNet data networks link all six-plant areas, with a myriad of DeviceNet networks drawing data up from plant floor devices such as drives, motor starters and valves. All data communication between buildings is routed via multimode fibre-optic cable, to ensure maximum data integrity.
At the operator interface end, 10 PC-based HMI stations running RSView32 operator interface software provide access to the plant's 60 000+ process tags. The flexible nature of the ControlLogix architecture proved to be one of the system's greatest benefits. The ability to share I/O and databases across different controllers located in different chassis was a key benefit of Control-Logix. This was particularly so in dealing with shared process facilities such as the plant's 6-bay milk reception area.
ControlLogix also permits multiple controllers to be sited in a single chassis. This was used to advantage in the system's dryer and evaporator control chassis where multiple controllers were installed for reasons of control algorithm integrity and capacity.
Integrated open networks
Access to system data via widely integrated open data networks was an Anchor-essential for the new dryer control system. Efficiency of data throughput was also crucial, with Anchor demanding speedy I/O updates and HMI screen refresh cycle times of less than one second. Allen-Bradley's efficient three-tiered communications architecture proved ample. Two separate networks of switched Ethernet are routed about the plant to provide controller to HMI data communications. The first network routes data from the 12 ControlLogix processors to two pairs of duty/standby RSView32 active display servers; the second carries data from the servers to the 10 RSView32 HMI clients. RSLinx, Rockwell Software's server-resident communications engine, facilitates all HMI data transfer. Two networks of 5 MB/s ControlNet form the 'control layer' of the data communications system - the first for controller to remote I/O rack communications and the second for peer-to-peer messaging.
A device-level layer of the CAN-based DeviceNet network completed the 3-tiered open communications architecture. Around 60 DeviceNet scanners support the Dryer's 1640 DeviceNet nodes. It is estimated that this equates to almost 5000 discrete I/O, realising significant savings in point-to-point I/O cabling and hardware. While DeviceNet had been used at the Te Rapa site on earlier projects (the 1997 development of its cream products plant), it was limited to motor starters and variable speed drives. The Dryer 5 project extended the network's use outside the switch-room, with the vast majority of DeviceNet nodes - some 1100 - linked to Dryer 5's DeviceNet- enabled process valves. Via the Dryer 5 DeviceNet network, important process valve information may be accessed including stroke times, actuator frequency and valve diagnostics. Variable speed drives and MCC-based DOL starters make up much of the remaining Dryer 5 DeviceNet nodes.
The network retrieves critical data from the plant's 260 DOL and variable speed drives, ranging from 1,1 kW lubrication pumps through to the 600 kW evaporator mechanical vapour re-compression fans. Smaller DOL starters interface to the network via the Allen-Bradley DeviceNet System Accessory (DSA) module, a compact 22,5 mm wide DIN-rail module. Mounted in the MCC's wiring duct, these provide each starter a simple two inputs/two output DeviceNet interface points. Larger drives are fitted with SMP-3 electronic overload relay which also afford DeviceNet connectivity.
DeviceNet has also been extended to more elaborate field devices, including a proprietary inline milk analyser. Here, the single DeviceNet connection retrieves 18 individual realtime analog signals, representing the milk's percentage fat, protein, lactose and other parameters. DeviceNet also allows commands such as line purge, analyser mode change and so on, to be written from the ControlLogix system to the analyser.
No facility within a plant is an island; linking from Dryer 5 to other existing Te Rapa plant areas was also a must. Using the ControlLogix' Gateway and network interface modules, data links have been realised from the Dryer 5 ControlLogix system to other Allen-Bradley PLC-controlled Te Rapa plant areas, either via ControlNet or via the DH+ and remote I/O networks. Linking into the plant's three existing dryer DCS control systems has proved more challenging. Here, the CSE design team developed an ingenious PC-based gateway, linking the ControlLogix system to the legacy-DCS. The gateway forms a bridge between the new dryer's control Ethernet and the DCS's serial interface.
To the future
In the longer term, Anchor Products Te Rapa plans to widen its 'data net' by extending the Ethernet/ControlNet/DeviceNet architecture deeper into the site's existing manufacturing and service areas. The immediate Dryer 5 goal is to build an operational database over its first year. This will allow development of an appropriate process model and ultimately the application of predictive control to the new dryer. The ControlLogix system and its powerful data communications capabilities has provided the practical means to collect this data and ultimately realised the 'neurallink' to the information-rich system conceptualised by Steele and his team a decade ago.
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