"We wanted to leverage the spare parts, internal technical knowledge and technical support that we were already getting from Rockwell Automation." Kimberly-Clark's Bob Kilas on the company's decision to migrate its aging DCS to a unified architecture based on the PlantPAx system.
The legacy DCS architecture used proprietary controllers for the analog I/O and a proprietary network interface to older Rockwell Automation PLCs that ran the motors and on/off valves in the wet and dry ends of the machine. The DCS also used a proprietary structured text language programming system, where the PLCs used ladder logic. The legacy DCS had 80 PID loops, 180 analog inputs, 60 analog outputs and numerous HMI tag groups. It had 65 HMI process graphic screens and 30 programs written in the proprietary structured text code.
"We had to hire back a retiree who had institutional knowledge of the graphic screens to capture the programming knowledge behind these HMIs," Kilas said.
This project was done in parallel with other projects and wasn't part of the machine-down critical path. "We needed to do it while the machine was running," Kilas said. Kimberly-Clark used a common HMI application and replaced the legacy controller, PLC gateway and HMIs, and eliminated obsolete PLC5s. "We migrated the ladder logic," Kilas said. "We needed to minimize conversion risk, engineering effort and down time so we did not rewrite the legacy structured text language code, just ported it to ladder."
Describing the lessons learned from this migration project, Kilas said, "We should have re-written the legacy structured text language code, and after the project, we did do that. We needed to define and do alarm rationalization. We need to provide system status and Ethernet switch health HMI screens. We absolutely have to ensure operator and maintainer training to cope with variations in operator knowledge and experience and use off-line simulation for automation sequences for training."
The project took 26 weeks from start to the finish. Kilas said, "We improved operator and maintainer efficiency, reset our lifecycle clock from 25 years to new and going forward, we now have a single architecture and engineering system for the plant."