Powerful data-acquisition system for sophisticated extrusion analysis.

If a more detailed view of your extrusion process is what you want, then you may have a new way of collecting enough data to paint that enhanced picture. Dow Plastics in Midland, Mich., recently commercialized a data-acquisition system that it once used in its own pilot plants.

Called Camile, the system is supplied as an integrated hardware/software package (see PT, Dec. '93, p. 59). The hardware component receives data from standard extruder thermocouples, pressure transducers, and other input sources. Camile TG software, which runs under Windows, provides a graphical user interface and networking capabilities.

This revamped Camile product springs from an earlier-generation system that first appeared in the early '80s as a data-collection tool for use on internal and customer lines--and later as a commercial system for laboratory applications.

Sized to fit in a suitcase, early Camile systems typically would travel with Dow technical-service staff to customer plants. Once there, the engineers would hook the device up to troublesome extrusion line and collect transient process data--sometimes more than several hundred thousand data points. Later on, the reams of data would be analyzed on a personal computer.

The updated and more commercially appealing version of the product preserves the data-collection capabilities of earlier generations while strengthening its control functionality. So, information collected by the system can still be downloaded into a PC for analysis at a later time. But now the data can be applied to real-time extrusion control.

Nowadays, Camile can even serve as the backbone of plant-wide CIM in mid-sized extrusion and compounding applications. Thanks to the system's networking capabilities, users can link multiple Camile boxes to a host computer via Ethernet--in essence creating a plant-wide control network.

TROUBLESHOOTING

In keeping with its origins as an in-house diagnostic tool, most of the extrusion-related application information stem from Camile's use by Dow engineers. In fact, the device even has played an uncredited role in some of Dow's technical papers over the past five years. And at the upcoming SPE ANTEC in San Francisco this May, the system's abilities as a troubleshooting device will be the subject of a paper by Dow project leaders Kun Hyun and Mark Spalding.

According to Spalding, Camile has been especially useful in understanding why an extrusion process sometimes strays unexpectedly from steady-state operation. Once the process does cross into an "unsteady state," it is subject to fluctuations in temperatures and pressures--and ultimately, in the product dimensions themselves. "Transient process data" collected by Camile enable complex correlations of the many variables associated with steady- and unsteady-state behaviors. With such data in hand, Spalding says, corrective action can be taken by modifying the screw, resin, or process parameters.

One such case involved a Dow customer's 6-in., 40:1 extruder producing an ABS product. Every few days the process would suffer from unexplained and unpredictable flow surging problems--and a dimensionally unstable product. After collecting 300,000 data points from 17 barrel-temperature zones, two pressure sensors, and the downstream equipment during a three-day trial that covered both steady- and unsteady-state operation, Hyun and Spalding ultimately found the culprit: a periodic breakup of the resin solids bed in the screw channel. Fragments of the bed would subsequently lodge in the screw's spiral mixing dam, causing surges. Based on information from Camile, the dam was later modified and the surging problem disappeared.

Other flow-surging mysteries--ones also rooted in poor solids conveying--have been solved with Camile-influenced screw changes, Spalding reports. The Camile system has also seen use in resin comparisons and in extrusion research into optimum throughput rates for a given process.

NEW USE IN CONTROL

Camile has seen significant changes in its transformation from diagnostic tool to a control system. "Before, Camile wasn't suited to applications where you needed a PLC," says project leader and control engineer Dave Daniel, who cites high-speed machine sequencing as an example. "But wherever you needed analog control, it has always been very good."

With the new Camile release, Dow has addressed the two major limitations that kept it out of the extrusion control realm in the past--scan speed and I/O capacity. The system's new I/O boards, called SmartBoards, have a 10-Hz scan rate regardless of I/O count--a tenfold improvement over earlier models. "You get faster control throughput," says Daniel, explaining that the system updates its output more frequently. And the system now accommodates a greater I/O count--up to 1000. "Before, anything more than a couple hundred I/Os and there would be a better solution," says Daniel.

Other changes have infused the system's man-machine interface (MMI). Unlike a PLC, Camile does not have much separation between the MMI and control programs; Camile's control programs are the operator interface.

For user-developed automation applications, Camile can still be programmed textually. But Camile TG software also enables users to create control applications graphically by simply linking objects on their computer screens. "If you can draw a process flowchart, you can program the Camile system," says marketing manager Linda Bakke. To further ease programming tasks, Camile TG includes predefined data displays, predefined PID algorithms for continuous control, alarms, and trend graphs that record process data in real time for monitoring purposes.

Price, which depends on I/O capacity, ranges from just under $10,000 to over $50,000.