Retrofitting a control system is tricky. Doing it and maintaining a 10-fold quality lead might seem impossible, but that's what engineers at Kemlite Co. (Joliet, Ill.) recently accomplished on one of three fiberglass-reinforced plastic (frp) panel lines.

Kemlite's panels are used in truck linings and roofing, RV exteriors, and as wall and surface paneling in cleanliness-demanding environments. Kemlite ensures its panels are as nonporous as possible and 10 times easier to clean than other frp by using a production process that doesn't "commit" the final chemistry until the frp's polyester resin is poured simultaneously with its hardening compound onto the line's polyester carrier film. This quality makes Kemlite's Glasbord frp the most specified in the U.S., especially in the health care and food industries.

To implement its Year 2000 plan for renovating its control system, communications, and human-machine interfaces (HMI), Kemlite began by exchanging its antiquated DOS-based HMI software for a Microsoft Windows environment, installing Siemens PLCs, and replacing field device hardwiring with Profibus-DP.

This meant removing old manual controls, analog sensor inputs, and 10-year-old, hardwired PLCs with obsolete proprietary remote network. These were replaced with faster, smaller, memory-intensive Siemens PLCs, which were arranged in an open-architecture "communications pyramid" with low-level field devices and administrative mainframe computers using a common PLC language. Field-level communications were moved to Profibus-DP, which allowed Kemlite to replace individual parallel hardwiring with a single twisted-pair cable. This simplified system configuration and reduced $1,000/hr downtime costs, because control cells could now be tested offline and installed during regular maintenance and shift changeovers.

One of the most important improvements was the installation of an inexpensive HMI supplement that uses Microsoft Excel, Visual Basic subroutines and DDE communication software, and also talks with the PLC via Profibus-DP. Where the previous HMI could only log data reliably at 5-to-15-min. intervals, the new computer stations capture data from Kemlite's frp line in 15-sec. intervals. This provides rapid updates of production profiles, such as exothermic temperature readings of chemical reactions, which are crucial to the frp's overall quality control.

As a result, Kemlite is saving 40% to 50% on typical project costs. Its Joliet plant runs 10-15 projects per year, and Kemlite plans to standardize on Profibus-DP and Siemens PLCs. Profibus-PA likely will be added to complement Kemlite's Profibus-DP and Profibus-FMS configurations. The new HMI system may also use ActiveX. Object-oriented programming and greater use of Profibus optical connectivity will also be explored.

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