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Tools are the key to successful Profibus implementation

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article image Coriolis flowmeters on Profibus PA

When Coopers Brewery relocated from Leabrook to Regency Park in 2001, the company took the opportunity to expand its capacity by commissioning an entirely new brew house.

International brew house designers Briggs of Burton proposed linking all measuring points with a Profibus communications system, based on its outstanding success in other brew houses worldwide.

Recognising that Profibus technology would effectively ‘future-proof’ the company’s new plant, MD Dr Tim Cooper agreed and Coopers thus gained Australia’s first Profibus PA-networked brew house.

Even today, the Coopers brew house remains one of Australia’s most modern brew houses. Its state-of-the-art Profibus technology includes both Profibus DP (utilised in the control room to link the PLCs and SCADA), Profibus PA (utilised extensively throughout the plant for the measurement and control of level, temperature, flow, pressure and valves) and ASi bus (for the digital I/O).

Also installed were power meters, temperature, pressure and level transmitters and flow control valves.

Successful commercial brewing depends on the accurate management of a highly complex series of processes. Precise, integrated process data on density, flow, level, pressure, pH and temperature are crucial for effective process control.

According to David Medlyn, Senior Process Control Engineer at Coopers Brewery, since the introduction of Profibus, his process managers are now obtaining more accurate and immediate feedback on every measurement parameter and measuring point at all process stages.

Better process control has also increased the efficiency of subprocesses within the brew house – such as the collection of spent grain and CIP processes.

Medlyn and his team did have to work through a few issues as part of their learning curve – most notably in the area of communications. Medlyn explains: “Communications can be lost if the last node in a segment loses power. This interferes with the termination resistance of the segment and can pull down the entire network.”

Australia’s only accredited Profibus International Competence Centre (PICC), established by Pentair Flow Control Pacific, states that a termination resistor must be placed at the ends of each segment to prevent this problem from occurring.

“If using a powered termination resistor it does not take an address on a segment, but does represent a device and a maximum of 32 devices can be linked in a segment,” explains Vladimir Vukovic, Tyco’s Engineering Manager – Process Automation, at the Competence Centre.

“Slave addresses must be allocated carefully and recorded by the installer,” he adds.

If a device is set to an address that has already been assigned to another device, it will cause conflict errors.

“Although best avoided in the first place, double addressing can be easily picked up by an analysis tool,” notes Weyman.

Planning and installing networks have indeed come a long way with the introduction of advanced analysis tools that make it easy to locate faults and get detailed network information.

Weyman is also a strong advocate of proper documentation. “When installing large networks one must be careful to ensure adequate documentation is produced and checked off I may be stating the obvious but it is easy to overlook some installation and commissioning checks,” he notes.

Brew houses are typically harsh environments whose high temperatures, aggressive processes and caustic cleaning materials can be hazardous for workers and machinery and damaging to cabling. By radically reducing the amount of cabling needed within the Coopers brew house and enabling process instruments to be added quickly and easily into the network, Profibus radically reduces the potential for cable damage and the time, costs and dangers associated with maintenance. Furthermore, Profibus enables ‘plug and play’ commissioning.

The programmer simply obtains the relevant GSD file, adds the new node onto the segment and with an update to the control logic it’s ready to go.

One of the key advantages of Profibus is its flexibility – minimal additional cabling is required when extra nodes are installed. Medlyn is particularly impressed by the robust performance of Profibus PA, and the simplicity and convenience of its troubleshooting capabilities. When an instrument is damaged, the Profibus network does not fail and the source of the problem is instantly identifiable from the control room.

Process managers can also proactively prevent instrument failure by remotely detecting incipient problems and pinpointing where attention is required. This reduces process down time and batch wastage and minimises resources spent on maintenance.

Having experienced the benefits of using Profibus PA and seen the resultant increase in the quality of its products, Coopers is continuing to introduce Profibus PA throughout the remainder of the plant as it upgrades and expands to meet growing market demand for its products.

“We find that the 4-20 mA loops in our plant require more calibration work and are not as reliable or as accurate compared with those on the Profibus network,” concludes Medlyn.

The Coopers team has deployed ProfiTrace as the predictive maintenance tool across the network. This powerful analysis tool enables technicians to check and troubleshoot the complete Profibus network and thus plays a significant role in plant asset management at Coopers Brewery.

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