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Dairy milks data to meet export regulations

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Building on an automation network linking 10 separate factories, NZMP Whareroa has taken the next step in plant optimisation by collecting myriad plant-floor data from its factory PLCs into a single central database.

Located on New Zealand's North Island, the plant is owned by NZMP, the manufacturing and marketing division of Fonterra Co-operative Group Limited. Owned by more than 14,000 NZ dairy farmers, Fonterra is NZ's largest company.

Processing over 14 million litres of milk a day, the site operates 10 individual manufacturing plants, and controlling all this is one of the largest automation systems in the Southern Hemisphere. Divided among nine operation zones, the system comprises 230 Allen-Bradley controllers and over110,000 I/O points.

Recognising the wealth of data residing within the plant-floor controllers, NZMP Whareroa automation engineering team leader Dave Gallie first dabbled with Rockwell Automation 's industrial transaction manager, Rockwell Software RSSql in 1997. According to Gallie, the original drivers for installing RSSql were to monitor and record key performance indicators (KPI) for each plant.

If it was the general KPI demands that started it all, it was the particular needs of the Cream Products plant - specifically the butter packing lines - that kicked it along. Tighter regulations introduced by the NZ government in 1999 demanded documented proof for butter carton weights as an export prerequisite. With 95% of the site's annual butter production of 80,000 metric tonnes exported, the data transactions initially desired for process optimisation and trace back rapidly became a commercial necessity.

The butter plant converts fresh cream into 600t of butter a day. Following the butter churning process, the finished product is pressure-fed into storage silos on each of five packing lines. Butter is then pressure-fed through two fill-heads at the base of each silo into a pair of ready-made, paper-lined cartons. Volume is set by an encoder to correspond to a weight as close as possible to 25kg. The carton then moves to the final dosing station, where it's topped up by another encoded hydraulic ram.

"In order to make sure that no under-weights were exported, we used to add a bit extra; but all those tiny top-ups added up to considerable tonnage, which put us over quota," Gallie says.

The company needed a solution that would allow accurate documentation of the exact weights it was exporting, as well as refined control of the carton filling process itself.

According to NZMP Whareroa automation engineer Geoff Roberts a critical issue was the existing automation network for the packing lines. With two out of five lines controlled by a manufacturer's proprietary controller, it was difficult to make process modifications. Since the rest of the factory is standardised on Allen-Bradley PLCs, Roberts says it made sense to replace the proprietary controllers with PLC-5s.

"We wanted to integrate the bulk packing lines with the rest of the plant--both upstream and downstream," Roberts says.

The resulting system comprises five Allen-Bradley PLC-5/20E controllers, one for each packing machine, linked by a DH+ network. Each controller is in turn connected via DeviceNet to a dedicated Toledo Jaguar final weight and tare scale. The scale measures the block weight before and after the final dose, taking into account the tare weight of the carton.

Control algorithms compare the bulk weight with the average of the previous five cartons and send any required ram position adjustments back to the bulk fill encoder, which is set to deliver 24.850kg. Similarly, the final weight is compared with the average of the previous eight cartons and the doser fine-tuned to ensure a final carton weight of as close to 25kg as possible.

It is this exact final weight, along with date/time stamp, cypher and packer number, that is extracted out of the PLC by RSSql and deposited into the central database.

According to Roberts, running RSSql with RSLinx (as the OPC server communications interface) on a separate dedicated computer has provided unprecedented speed and reliability of the vital datalogging. "It's so easy to run queries now," he says. "One of the major advantages is the ability of RSSql to document which fill-head a carton has come from. This is really important for trace back and trouble-shooting."

Gallie and his team have applied RSSql in many other parts of the NZMP enterprise, including the Whareroa plant's Milk Reception area and the company's North Island milk transport operation business. Here, RSSql provides the real-time data necessary to realise synchronised milk storage, pumping and transport activities.

The data transactions handled by RSSql, through its seamless connection with the plant-wide Allen-Bradley PLC network, have become an integral component of the facility's operations. Not only do they provide the export documentation so crucial for regulatory compliance, they also form a critical link in the whole chain of milk deployment, processing and quality control around the Whareroa facility - real-time data straight from the plant-floor itself.

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