The Batch Control Challenge
By: Robert Wenstrup Marketing Manager, Application Systems Allen-Bradley Company
Food processors face some tough production challenges. The goals are to reduce the cost of production, rapidly convert from one product to another, improve quality and reduce the time it takes to produce new products.
Success in achieving these goals depends, in large part, on automating the food-processing control system. Critical decisions include matching hardware/software functionality to the unique requirements of food processing, and finding the right help for a successful control system implementation.
The challenge in batch process control is to reduce the cost of production, rapidly convert process lines from one product to another, improve product quality, and reduce the time to market for new products.
There is also the need to cope with a wide range of equipment, from a variety of vendors, that usually does not possess the flexibility required by a batch application. Dependable vendor support in establishing a batch control system and in providing long-term support is often a problem. Control flexibility is key because of the high cost of batch process control equipment and because long-term process migration and product-line upgrading is limited by equipment dedicated to a single process.
The use of a wide range of control and reporting methods limits the ability to coordinate multiple process lines and benefit from a greater centralization of process control and reporting.
Vendors able to help throughout the control implementation cycle are hard to find. Few have dedicated themselves to batch applications to the extent that they can actively assist in planning, cost justification, design, project- implementation, installation, start-up and on-going process maintenance.
HOW AN AUTOMATED CONTROL SYSTEM CAN MEET THESE NEEDS Batch software should provide for a broad range of data gathering and analysis and provide multiple logs of process data. Significant flexibility should be available for structuring how the data is utilized for analysis, reports, etc. With access to the entire programmable controller data table, virtually every significant process variable is available for trending, pareto charts, alarm reports and many forms of statistical quality control analysis. All files should be collected and stored in an ASCII format, which provides for the broadest possible usage of available analysis and control quality software.
MULTI-LINE COORDINATION
The coordination of several process lines into a flexible production process is a complex problem. A batch process control system based on programmable controllers interfacing with industrial computers simplifies the control task.
System conformance to the Instrument Society of America's SP88 batch- process control standards and to the European NAMUR batch-control standards provides the necessary structure for controlling a number of process lines with varying control requirements.
STRUCTURED ARCHITECTURE
The structure of control architecture is another element of success. The ability to incorporate many different forms of equipment and software programs into a process line will increase the value of the control system over time. The control system should be flexible enough to allow for rapid incorporation of new technology. Similarly, batch process control software should be flexible enough, without sacrificing structure, to allow for easy modification of operator screens, data collection and reporting routines, and recipes.
UNIT ALLOCATION
The ability to run multiple batch lines concurrently improves process-unit allocation and results in optimized process equipment utilization. With a structured approach to process unit allocation, a control system has the ability to recognize individual process unit operations so once an operation is completed for a given batch in a given process unit, the next batch operation can be started in that unit.
SYSTEM MODULARITY
A modular batch process control system lends itself to rapid, cost effective modification and upgrading. Increased production capacity and process improvements can be achieved by adding advanced software options (such as extensive reporting capability), additional control consoles, or by adding of a wide range of input/output modules to increase the number of field devices used in a process line.
FUNCTIONAL PARTITIONING
A very successful approach to batch process control is to integrate a programmable controller with a master industrial computer and optimize the system for batch process control. By partitioning the functions between a programmable controller and an industrial computer, the strengths of each can be exploited.
A programmable controller is designed to provide predictable closed-loop response to plant process line conditions. This strength is utilized by the creation of dedicated, optimized ladder logic control for batch process. Thanks to a structured approach to batch application, the amount of programmable controller code that must be created is substantially reduced.
An industrial computer is best suited for operator interface, recipe management and data acquisition. Batch products taking advantage of this strength provide configurable recipe management routines and configurable loop tuning capability. This substantially reduces the cost to create, modify, or upgrade a batch process control line.
HOW AN AUTOMATION PARTNER CAN HELP
The difficult process of coordinating multiple vendors is simplified by the pre-defined configuration of hardware and software. Pre-establishing many of the elements of the control system, such as the hardware to be utilized, the structure of the data table in the programmable controller, the communication network to be used, the batch console layout and keyboard layout, help to clarify application requirements for the vendors involved.
BROAD CAPABILITIES
Any batch-control vendor should have a wide range of application experience in addition to a broad product line which can cover simple batch processes, as well as complex processes with standard hardware and software. With a broad product line, many vendors can utilize the same control equipment to provide cost-effective solutions for a wide range of control problems.
A broad product line available for batch process control ensures that a significant portion of the system equipment which integrate well together by design. Finally, the ability to provide a complete turnkey batch process control system can significantly reduce the effort required to coordinate activities.
Often the needs of an organization cannot be totally fulfilled within the company. A batch process control vendor can lend significant support if he can assist in planning a project, help in design of the system and, if needed, provide full system implementation.
SYSTEM SUPPORT
One of the more challenging aspects of batch process control is the difficulty in getting blanket support for all of the elements of a process line. Equipment vendors, control vendors, software vendors, various internal organizations - such as plant operations, engineering and maintenance - all need to have a part in maintaining and improving the operation of a process line. A control vendor with a broad range of services can help reduce the complexity of process line support problems. Important resources include local support for day-to-day operational issues, product application support for complex product oriented issues, and engineered system expertise for complex, systems-level support issues.
An experienced, knowledgeable vendor can help plan the system, determine a cost for project justification, design the system, help implement the project, and maintain and upgrade the process line throughout its operational lifetime. Training for products and packaged systems should be available. Extensive documentation should also be available for on-site problem diagnosis and line modification.
Downtime is always a critical problem in maintaining production throughput. If rapid support for the key line equipment is not available, sooner or later the cost of maintaining the system will become prohibitive. A modular structure of the batch process control architecture also simplifies spare parts decisions which makes it more likely that the key spares will be on site when needed.