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Serial Communications at the Heart of Nelson Pine's New $100 Million MDF Line
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PDL sales engineer, Mark Duncan and Nelson Pine Industries senior electrical engineer, Lew Solomon in front of the line three dryer at the Nelson Pine Industries site in Richmond
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Nelson Pine Industries opted for PDL variable speed drives (VSD's) using an open universal protocol,
Modbus™, for the upgrade of its medium density fibreboard plant in Nelson. This option allowed Nelson Pine multi-vendor choice, improved process monitoring and simplified cabling.
In the past, once a company had chosen a supplier it was committed to its product, but the development of serial communication products using universal protocols, has allowed equipment from different manufacturers to be used in conjunction with each other.
Senior Electrical Engineer at Nelson Pine, Lew Solomon, said the company opted to use an open protocol using PDL
VSD's, rather than installing those of a competitor, when it embarked on the $100 million project to install a third production line in 1995.
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"I was keen to push through with Programmable Logic Controller (PLC) and drives that allowed serial communication on the third line because they give improved monitoring of the processes carried out at the plant. There is usually incompatibility between the different protocols but
Modbus™ allows us direct communication. To my knowledge there are only two or three products that can do this. Modbus™ also gives us wide freedom of choice when it comes to the purchase of products that we may want to use in the future".
There were also physical and economic benefits to taking the route opted for at Nelson Pine. "The great advantage of serial communication is the physical simplicity of wiring everything up. It simplifies installation by reducing wiring and the number of connections required," says Lew Solomon.
Lew, who has worked for the company for 13 years, helped establish the first line back in 1986. The second line was installed in 1991 and construction on line three began in late 1996 and was completed in October 1997. It increased the plant's production capacity by 60 percent. Currently the plant, recognised as the most advanced in the world, can produce 350,000 cubic metres of medium density fibre board per annum, primarily for the Asian and Australasian markets.
The manufacturing process begins with wood chips from radiata pine. Fibre is extracted and formaldehyde resin and paraffin wax are added before the material is dried to a specified moisture content. A continuous mat is formed at the beginning of the production line, the material pressed and then conveyed continuously through a Kusters Press. Following processing the panels (in a wide variety of thicknesses) are cut into lengths up to 7.2m and cured.
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| Lew said that while PDL variable speed drives were already standard on the other two production lines, the use of serial communication was new. "The decision to choose PDL VSD's to control the motors on equipment that needs its speed varied (i.e. including fans, screw conveyors, and belt conveyors) in the upgrade was made over numerous other brands. A number of other products were serious contenders but past performance of gear from PDL Electronics on lines one and two and good local backup from the company were deciding factors."
"We like to keep product loyalty, the plant runs 24 hours, seven days a week so if something works we want to stick to it" says Lew.
Data from the PDL VSD's is fed to the firm's Allen-Bradley PLC after going through a MARCTM
Omnii-Comm™ protocol converter. From there raw data, including information on temperature, pressure, logic states and machine status is monitored on the multi-screen, PC based visualisation system in the line three control room. Lew says "In the past the installation of Allen-Bradley PLC's would have meant the use of Allen-Bradley drives, but by taking the
Modbus™ route, we were able to use the PDL drives. It was a good choice because it gave us the capacity to go up in scale once the converter was installed".
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Lew Solomon and PDL sales engineer, Mark Duncan, discuss the benefits of the Xtraverts in the line three
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It is currently estimated that over 80 percent of installations using the Modbus™ protocol, originally designed by Modicon, Inc. Automation Systems for use with its own PLCs, are now used with products from other companies, indicating a customer tendency to chose protocol options that allow them the greatest choice of supplier.
Lew said the line three project included a "smorgasbord" of PDL products from the smallest Xtraverts through to a Microdrive-i 140 that had all been put on the same network using the ModbusTM protocol. "We used 30 Xtraverts for lower power ratings exploiting the serial communications feature they offer. I believe serial communication on this scale is unique."
It was also an excellent economic option. Nelson Pine decided that for a moderate number of drives or devices it is more cost effective to communicate serially than directly.
Serial communication has also resulted in improving the quality of data to the control room allowing Nelson Pine direct digital signals instead of going through an analogue intermediary. Generally Modbus has the capacity to interconnect well over 200 devices. At Nelson Pine Industries, using the MARCTM
Omnii-Comm™ converter it currently interconnects 32 including drives on the drum debarker, resin and wax system and a number of variable speed fans.
"Xtraverts used in the project demonstrated the huge potential of a relatively cheap device" said PDL Sales Engineer, Mark Duncan. "Even though it is small and at the bottom range of our equipment, it is able to communicate serially, something that is normally reserved for larger drives."
"We are delighted with it, the system works well" says Lew. "With line three successfully up and running, it is likely that a serial communication system will be used to upgrade line one within the next five years."
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