Better Control of Batch

March 30, 2003
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Standards that leverage open computer architecture hold promise of significantly greater batch processing automation.

Batch control systems like National Instruments' Lookout replace mechanical switches and counters and minimize the risk of human error for clients such as Blue Bell Creameries. (Source: National Instruments)


Food processors' demands for equipment integration are pushing suppliers such as Key Technology to offer modular control systems for batch processes.
When electricity in the home was still a novelty, American power generators promoted each new electrical appliance as a labor-saving device. After 40 years, the popular joke was that American housewives had so many labor-saving devices, they no longer had time for anything else.

There's a parallel to the current state of batch processing in food plants. Great strides have been made in the last 20 years to automate batch operations, with machine muscle replacing human toil, but operators and engineers still find themselves mired in repetitive, error-prone tasks and burdensome procedures when a change or correction must be made.

Much of the blame can be attached to the lack of uniformity in conceptual models used to define batch control systems. One engineer describes it as "a Tower of Babel state of affairs," with different companies and different groups within the same company applying their own logic to systems. The result: even when equipment from multiple vendors is integrated, any changes force a code rewrite for each PLC.

The need for standardized specifications for batch control systems has long been recognized. In 1989, the SP88 committee of the International Society for Measurement and Control, better known as ISA, began addressing the issue.

In 1995, the committee published part one of S88, which focuses on standard models and terminology for batch control. Part two, which addresses data structures and language guidelines, will be published later this year.

S88 holds significant promise for food processors, particularly in a production environment where manufacturing flexibility is causing even those with continuous processes to rethink the benefits of batch. Batch processes can provide greater control and easier correction when things goes awry.

Reductions in troubleshooting time and manual calculations and paperwork, simplified recipe changes, better understanding of ingredient usage and greater flexibility in mix-making are some of the benefits attributed to batch control integration through S88. Some manufacturers credit the standard with slashing product variability rates in half. But although S88 had its genesis in the food industry, only a handful of firms such as Unilever and Nestle have adapted their batch systems to it. The greatest application is occurring in petrochemicals, pharmaceuticals and other business sectors.

A survey by ISA last year indicated only 25 percent of food companies were even aware of S88. An ISA staffer estimates perhaps a third are now aware, but the vast majority of firms are not realizing the efficiencies of S88.

"S88 is a design philosophy that lets you manage recipes and segment operating plants in a modular fashion," explains Jim Parshall, an automation engineer who helped implement an S88-based batch control system during his five years at Ben & Jerry's Homemade Inc. "The modularity that S88 promotes is the key benefit." Last year Parshall accepted a position with Eli Lilly and Co., where he recently was named a site automation engineering leader.

The bigger food companies are getting on board with S88," Parshall says, "but that might not be the case among smaller companies, and they really should be taking advantage of it." More troublesome is that equipment manufacturers are not necessarily embracing the standard, which means their food company clients won't reap the benefits.

Part of the lag may be because equipment manufacturers don't recognize how S88 can help their own businesses. Basic codes to run pumps, valves and other equipment are essentially the same for all the systems those manufacturers install. Instead of rewriting those codes with every installation, suppliers could build a library of modular codes and use them on subsequent installations, without giving away another customer's proprietary coding. That would mean faster installation of large projects and -- equally important -- quicker and easier verification of those systems.

That was the case at Ben & Jerry's St. Albans, Vt., facility, which serves as a how-to illustration of S88 application in the recently published book, Applying S88: Batch Control from a User's Perspective, coauthored by Parshall and Larry Lamb. The book explains how S88 provided a framework for upgrading the mix-making batch control system at the plant and outlines some of the benefits, particularly the integration of data and equipment control made possible through the sequencing that S88 dictates.

Recipe management receives most of the attention in discussions of S88's benefits. Recipes reside in multiple places, including a general recipe at the corporate level, a site recipe at the plant, a master recipe and the recipe executed by the operator. If recipes never changed, S88 wouldn't be an issue; of course, they frequently change, and there is a strong likelihood that the changes won't be made consistently throughout the recipe hierarchy if multiple codes have to be rewritten.

Parshall's book illustrates this problem with the case of an ingredient change at Ben & Jerry's. Somewhere in the recipe chain, codes were not rekeyed to reflect the change. Because of the sheer number of batches being run, the unnecessary ingredient's cost would have exceeded six figures within six months. By automating recipe management, the likelihood of that kind of error is minimized.

The logic behind process control tasks in S88 is depicted in this schematic. It is one component of what S88 developers call the Cactus Model. After being initialized by another component of the hierarchical model, the Execute Equipment Phases module sends commands and parameters to equipment, the Execute Basic Control regulates changes in equipment and process states by sending commands to control modules, and the Collect Data module retrieves data from sensors or from events that occur within the process control activity. Source: Applying S88: Batch Control from a User's Perspective, by Jim Parshall and Larry Lamb. Reprinted by permission of ISA.

Two steps forward, one step back

Standardization was less of an issue when companies were creating legacy systems. With today's emphasis on open architecture, data corruption becomes a serious concern as data pass from point to point. This is particularly so as plants move to open systems to run integrated equipment from multiple vendors. "The more people and systems information has to go through, the greater the likelihood it will be messed up," observes Dennis Brandl, director of enterprise initiatives with Sequencia Inc. Information that is inaccurate, untimely, or improperly assembled poses a serious quality problem for batch processors.

One solution is the development of "intelligent tags" that automatically generate information for multiple uses from a single definition of the tag. Such tags are at the heart of an S88-based software system developed by Sequencia client Morinaga Milk Industry Co. Ltd., a Tokyo-based firm that ranks as the eleventh largest dairy in the world.

Speaking at Food Engineering's Plant Automation 2000 Conference, Morinaga's Akitoshi "Tony" Sugiura described how his process automation group developed StageOne, a batch control system that minimizes programming needs and generates data on a given function for different areas of the plant. An example is a butterfly valve that opens and closes to let material pass through: by arming the valve with an intelligent tag, data are generated for operation, maintenance, control logic, graphics, status and reporting. Maintenance wants to know how many times the valve opens and closes for purposes of maintenance scheduling; inventory needs to know how much material is being used for purposes of reordering. By having a single way to manage and store PLC code for all plant functions, management is assured everyone is working with the same, accurate information.

"We are using an object-based method and the intelligent tag to implement the process control system," Sugiura explained. "It delivers easy-to-use tools to the operators, who are noncomputer/technical specialists." That allows operators to make changes to the process control system, he said, instead of relying on engineers or specialists to customize it.

The intelligent tag converts raw signals from, for example, a valve directly into input signals, output signals and error information. After the registration of the tag is completed, operators can use it in computer display, historical databases and maintenance systems. Instrumentation installation is the responsibility of engineers, while the use of the tag's information in production sequences is handled by operators.

"Bigger food companies are getting on board with S88, but that might not be the case among smaller companies." -- Jim Parshall, former Ben & Jerry's automation engineer

PC-based system upgrades

Improved consistency and rapid changeover are among the benefits realized at Blue Bell Creameries in converting to PC-based controls from mechanical switches and counters for blending operations. "It has eliminated the possibility of human error," says Keith Jenkins, process system technician at the Brenham, Texas-based dairy processor.

Four years ago, the maker of premium ice cream automated the batching system at its Brenham facility, later updating controls at plants in Broken Arrow, Okla., and Sylacauga, Ala. The software is called Lookout, from National Instruments in Austin, Texas. Two Siemens PLCs feed into the Lookout PC, which keeps batch set-up time to a minimum. The application features 171 preset inputs/outputs, two screens with easy-to-use human-machine interfaces, and an ethernet hub to improve the speed of communication.

The plant has three blend rooms, with the largest (5,000 gallons an hour capacity) still mechanically controlled. An operator still must turn rotary switches and verify that valves are open and pumps are running when product leaves the balance tank to the storage tank.

The other blending rooms have capacities of 4,000 and 4,050 gallons per hour, and it is here that short-run flavors are formulated. "In the past, the machine told you what you had to do and when you had to do it," Jenkins says. "Now, it is all automated, and the lab people and the guy in the blend room have control over what is going on."

The system's open architecture significantly simplifies rollouts of new products, as was the case earlier this year when the dairy introduced Moo-lenium Crunch, a seasonal item that quickly became a year-around favorite. The item was formulated in the headquarters lab and downloaded to controls in the plant.

"Open architecture has really improved things in our labs," Jenkins notes. "We can develop product here, put it into Lookout, and immediately begin production."

Lookout uses an object-based system for modeling, explains Ganesh Rangnathan, product manager at National Instruments. Each control function -- a PLC driver, for example, or an alarm or on/off switch -- is an object in the model. The client must select each object to be connected and then interconnect them. Although the objects conform to S88, the model is not overlaid with an S88 engine, such as Sequencia's oBatch used by Morinaga Milk or RSBatch from Rockwell Software used by Ben & Jerry's. S88 compliance is possible, but "it's not something customers can do straightforwardly," Rangnathan allows.

A more basic control system called Forte is offered by Key Technology Inc., Walla Walla, Wash. Forte is an off-the-shelf replacement for switching hardware and mechanical control devices. "The food industry has lagged behind in process controls that can link a system into a PC," says Randy Unterseher, product management. Forte was Key's response to food clients' demands for greater automation in batch processing. But Forte and similar systems are intermediate steps in the move toward consistent sequencing for managing activities. They help run the steps in a batch process, but they stop short of the comprehensive solution possible with S88-based systems.

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