Simulation software removes bugs, provides training

Armstrong World Industries, with 86 plants and 20,000 employees in 14 countries, is a leader in floor coverings. At its South Gate, Calif., plant, the company makes commercial and residential floor tile using various batching techniques.While recently replacing relays with Allen-Bradley PLCs and Wonderware human-machine interface software, plant personnel needed to debug PLC code and trai...

10/01/2000


Armstrong World Industries, with 86 plants and 20,000 employees in 14 countries, is a leader in floor coverings. At its South Gate, Calif., plant, the company makes commercial and residential floor tile using various batching techniques.

While recently replacing relays with Allen-Bradley PLCs and Wonderware human-machine interface software, plant personnel needed to debug PLC code and train operators how the batching process would work using the new hardware and software. Previously, training involved toggle switches, pilot lights, thumbwheel switches, potentiometers, and summation boxes for load cells to simulate plant operations.

"It was like musical chairs, with engineers toggling switches and turning pots," says Bill Mackin, senior project engineer at South Gate.

Mr. Mackin gained experience in PLC debugging at a similar batching plant in Jackson, Miss., which also replaced its batching system with PLCs. He used PICS Simulation software from SST (Waterloo, Ontario, Canada), part of Woodhead Connectivity, to debug PLC software.

Mr. Mackin says, "The PICS system is a great debugging tool, but its ability to emulate the plant, help resolve operational problems, and train operators has even more value."

PICS Simulation Version 3.3, for Microsoft Windows, is an I/O simulator for testing PLC-based control systems and for training operators. It allows the user to quickly create a dynamic model on a PC that duplicates the behavior of the process to be implemented and provides the PLC with feedback. To the PLC, there is no difference between controlling the PICS model and the process.

PICS has a graphical, object-oriented development environment that reduces time and effort required to create a process model; an enhanced device library saves setup time. The software has separate modes for training and development.

"The batching system at Jackson has seven different PLCs," says Mr. Mackin. "We replaced relay logic with PLCs over an 18-month period. As we went along, replacing one system at a time, we used PICS Simulation to help debug each PLC program. I set up PICS to emulate each batching process, so we could debug without using actual plant I/O equipment."

Setup, training

PICS reduced debugging and setup time because it was no longer necessary for engineers to rewire hardware simulation equipment and switches for each PLC and each process. "We just changed a few settings in the PICS Simulation software to move on to the next step in the process," Mr. Mackin explains.

When adding enhancements and capabilities, though the programmers and engineers give the operators what they think is needed, problems sometimes come up. "We add enhancements, but when we get to the training portion, we find discrepancies between what the operators imagined they wanted and the realities of the actual process." Simulations allow details to be worked out in the training lab prior to installing the processing equipment and PLC, and hard-wiring the system in the plant.

When changing to a new tile pattern or recipe, operators put a machine into manual mode, clean it out, and go back to normal operations. "It's very easy to get out of sequence during special procedures, such as pattern changes and cleanouts, because there are many steps in each. We worked together to make enhancements to these processes, and the PICS Simulation saved us a lot of time."

Simulations correct problems

Batch operation problems go to the simulator, along with the operator or maintenance person who was involved, "to identify the problem and solve it," explains Mr. Mackin. He also used PICS' emulation capabilities to create a certification program for new operators.

"We never used this installation of PICS to debug PLC software the way most end-users do," he says. "Instead, we set it up to do operator training and solve plant operation problems." Mr. Mackin sees other value. "We work through the scenario and discover whether we actually have a bug in the software or process, or if it's an employee-related problem. Perhaps an operator doesn't know all the necessary procedures and needs more training. There isn't any good way to determine this without the simulation."

Average return on investment using a PICS system is less than six months, according to SST. (For more on simulation, see cover story, in this issue.)

For more information on SST PICS software, visit www.controleng.com/freeinfo .





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