Porting a Legacy Control System to a PXI Platform Running the NI LabWindows™/CVI Real-Time Module

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"Our delivered solution, based on NI hardware and software, met or exceeded all of our client’s requirements, maximized development efforts and reuse of legacy code, and saved more than $50,000 USD in hardware and licensing costs."

- Nathanael Mackley, Mantaro Product Development Services

The Challenge:
Replacing an obsolete critical control system for six hot rolling mill stands with a modern, flexible platform that requires minimal deployment costs, minimizes production downtime, and maximizes legacy code reuse.

The Solution:
Evaluating various technology platforms, including the VMEbus platform coupled with the VxWorks real-time OS (RTOS) solution, and ultimately selecting NI PXI hardware and the LabWindows/CVI Real-Time Module for the new control system based on deployed system and development tools costs, technological maturity and readiness, and overall support structures.

Author(s):
Nathanael Mackley - Mantaro Product Development Services
David Wheeler - Mantaro Product Development Services

A major steel manufacturer in North America needed to replace a critical control system for six hot rolling mill stands. The original hardware had reached obsolescence, and key components were unavailable or priced at premium rates. With a potential loss of thousands of dollars per minute of downtime, it was imperative to keep the production line running and avoid costly delays and downtime. The steel manufacturer selected Mantaro Product Development Services to implement a control system upgrade program to replace the legacy hardware with a modern platform while porting as much of the existing code as possible. 

Hot Rolling Mills: A Demanding Environment

Every aspect of a hot rolling mill requires awareness of the hazards involved, well-engineered components, and affordability. This is compounded when the mill is operational every day for 24 hours a day with no room for downtime outside of scheduled maintenance and service operations. Capital investments are large with support requirements extending well past 10 or even 15 years for the control and monitoring systems.

Figure 1. System Diagram of Hot Rolling Mill System

This particular mill had been in operation for nearly 15 years. The control system was built around the Multibus II platform and made extensive use of custom and proprietary hardware solutions from the original systems integrator. Electrical isolation was required to protect the Multibus platform from plant-wide and local ground loops and electrical surge. The new hardware platform would be required to meet or exceed the existing isolation performance. The legacy hardware was generally reliable, but typically required as many as 15 minutes from power up to reach run state. Reducing this start-up time was highly desirable, but zero tolerance for equipment and process failures stemming from unreliable hardware meant that changes to the state machines would be viewed as undesirable. The operational ANSI C code ran on the iRMX real-time OS. Each of the major control processes required its own processor, and each processor was operating at or above 80 percent utilization. The fastest processes were operating at 1 ms cycles and often depended on inherent latencies in the Multibus platform. Moving to a modern control platform presented an opportunity for significant application improvement.

Technology Platform Selection

When Mantaro Product Development Services was selected as the systems integrator, we evaluated the VMEbus platform coupled with the VxWorks RTOS solution versus the NI PXI technology platform and the LabWindows/CVI running on the Pharlap RTOS. Based on client requirements, the deployed system, development tool cost, technological maturity and readiness (specifically the use of an Intel Core 2 Duo class processor), and overall support structures, we recommended the National Instruments platform.

Figure 2. Technology Platform Cost Comparisons

The NI solution met or exceeded all of the requirements, demanded a significantly lower software license cost for development, and allowed reuse of the existing code through the LabWindows/CVI programming toolkit. A key value-added element of this platform was the NI-DAQmx driver base. NI-DAQmx reduced development effort by freeing the engineers from developing custom drivers for the hardware and will allow for simplified hardware changes in the future should a component require updating or enhancement.

Hardware Implementation

Our hardware engineers adopted a “plug and play” approach to system design. The entire upgrade system was located in a self-contained, standard 19 in. cabinet, permitting a single, common design as a drop in replacement for each successive control system in the entire mill facility. The signal I/O interconnect between the legacy and upgrade systems was a bundled bus design. This simplified the design of the cable and allowed the documentation to be reduced in complexity, thereby removing several man-weeks of labor costs. The signal I/O interconnect used the legacy interface with adaptation to the upgrade control system wiring schema occurring in the new cabinet. This allowed the installation of the upgrade system to add only a single point of change to the operational system during the development and test phases.

 Software Implementation

Our software engineers tried to reuse as much of the original code during the development process while adhering to the mantra of “do not break anything you touch.” The original code was ported from multiple processes in multiple processors to a single thread in a single real-time core of the new Intel Core 2 Duo based controller. Final breakdown of the code included 80 percent of the original code and approximately 20 percent of new code to support the PXI platform, a different RTOS, and several new features. The new architecture permitted the real-time processes to run serialized and at a synchronized 1 ms cycle.  

Long-Term Support – Looking Out 15 Years

The cost of implementing a control system upgrade in a large steel mill is significant, and the life-cycle support provided by the system vendors plays a key role in the “go/no go” decision. The offerings from NI were appealing to Mantaro as the system integrator and a form of research validation. As our preferred vendor, NI offered an array of options from basic, serviceable hardware design and warranties to long-term service and support agreements. 

The initial deployed system operated from the beginning with no system hangs and received and recorded data for analysis during the entire validation process. At the time of study, the project worked through nearly all test cases and is nearing the initial transfer of control to the PXI platform. Confidence in the new system has been affirmed through the following system stability characteristics:

  • No system hangs during six months of development
  • Faster response to hot mill changes than the legacy system
  • Reduced CPU load
  • Submillisecond latency on all process control signals

The NI solution provided a comprehensive set of development tools, hardware, and life-cycle solutions for Mantaro Product Development Services engineers to implement and deploy a modern control system. By taking advantage of our embedded and industrial experience with the highly regarded and affordable NI platform, we designed and constructed the hardware solution, ported the legacy code, and added new analysis and monitoring features to create a much more powerful and stable system.

Disclaimer: The mark LabWindows is used under a license from Microsoft Corporation. Windows is a registered trademark of Microsoft Corporation in the United States and other countries.

Author Information:
Nathanael Mackley
Mantaro Product Development Services
20410 Century Blvd, Suite 120
Germantown, MD 20874
Tel: 301-528-2244

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