1 October 2005
ISA-88: Bringing home the batch
Standard gives structure to complex process.
By Daren Moffatt
Whether because of tighter budgets, control centric engineering groups, or other reasons, some users still conduct batch operations manually. Even if they use the ISA-88 standard as a project philosophy, they still have a hard time justifying the additional batch management software. They will implement projects by writing extensive control logic in the PLC or DCS rather than using a batch management software product. When the project is approved, an automation project will use the ISA-88 batch philosophy during implementation, but not the actual ISA-88 batch management system.
Reasons for buying into batch systems
Although on the surface batch processing may appear to involve little more than turning things on and off, it can be deceptively complex. This complexity can add costs and jeopardize quality and consistency, which become critical in regulated industries such as food and pharmaceuticals.
The ISA-88 batch control standard is meant to help users get better. Since its first publication in 1995, the standard has become the common language to describe batch applications among users, consultants, and vendors. It provides a philosophy and guidelines for defining batch processes and a structure for effective automation. But despite the potential of batch automation to reduce operating costs and significantly improve consistency and traceability, quite a few batch operations remain manual. Although manufacturers work within the general guidelines of the standard, they miss out on benefits.
What is a batch automation package?
Batch management software helps manufacturers model and automate batch processes. By creating and managing recipes, materials, batch schedules, execution, batch history, and reporting, the software gives consistency to production and product quality.
While some small-scale batch operations may be better suited for manual operations, most manufacturers would see a quick return on investment in automation. But justifying the move from a process that is working to one that only promises benefits too large a leap for some companies' comfort is difficult. But the leap's worth taking for several reasons.
Reduced development cost is probably the best reason to automate batch operations. If you convert the cost of the batch software licenses into engineering man hours, you would only be able to develop a fraction of the functionality that even a modest batch package provides. And you would still have to budget time for software design implementation, testing, debugging and documentation. Some programmable logic controller (PLC) users have found not using a batch package can require 40% to 60% more logic just to accomplish the control objective, to say nothing of the history and reporting implications. For FDA regulated companies, this increase in control logic also comes with a larger demand for testing and documentation, making the additional costs significant.
Improved phase logic management: Without a batch executive, phase logic becomes more complicated. This is especially true in the case of applications with multiple connection paths between units. Some batch packages can manage these connections and their associated interlocking by using a connection-oriented process model. Handling the contention and interlocks without a batch package using phase logic complicates that logic, often resulting in spaghetti code and its associated testing, debugging, and maintenance nightmares. Since phase logic typically accounts for well over 75% of the project engineering effort, complications here can have a tremendous impact on the overall scope of the project, far beyond any savings you can achieve on batch license costs. This increase in the scope of the phase logic effort can also have an effect on the project schedule and risk missed delivery of the required functionality.
Reduced maintenance cost is arguably the biggest drawback to not implementing a batch package in a project. Commercial ISA-88 batch software imposes the ISA-88 philosophy on a user. This is a good thing; it generally forces the user to follow the ISA-88 equipment and procedural definitions. Basically, it imposes a structure to the control design rather than permitting the user to develop a custom batch application within the control system. As soon as the user embarks on a custom programming effort to reproduce some subset of the Batch package's functionality, he makes a commitment to support that application over the life of the installation, whether he knows it or not. Few people know how it really works, and they'll move on to other projects, jobs, and organizations. With a batch package, you can thoroughly document the functionality and support it with bug fixes. You can also take standard training courses. New users can get up to speed quickly and easily. And because of the standards, the number of people that understand how the application works, would be far greater than any custom application could hope. What is the potential cost of production losses over the life of the installation because someone with the right knowledge could not be found to fix a problem in time?
There are batch users in specialty chemical, pharmaceutical, and food industries that have projects to upgrade older batch systems implemented years ago using a custom approach. The users finally had enough of trying to support these home-grown solutions and want the structure that S88 and a batch management software package impose. Beyond just the simplification of the control code, the batch package provides a framework for managing the entire production process, from integration with the production planning system to production performance information.
Easier history and reporting: When a batch package is not available, the user must engineer the history of the batch events using the available tool set or operate the process without event data collection. Although some process historians can handle messages, they usually do not have the sophisticated query capability required for batch reporting. More importantly, the user must also engineer the generation of these messages, something the batch package would do automatically with no extra engineering effort.
Every event must now have explicit code associated with it to generate a message. This requirement to send messages containing the event information will fall to the phase logic. Not only should you not increase the requirements in this area, you need to engineer the generation and distribution of reports using available tools. Most commercial batch packages have a set of report templates specifically designed for batch. Custom implementation of history and reporting drives down functionality and reliability and drives up costs.
Greater production flexibility: If a manufacturing facility makes the same product constantly, manufacturers might design and implement the batch functionality into the control system, turn the system on, and let it run. In these situations, batch packages are not often deployed. However, as green field projects become scarcer due to the cost of new plants in most industries, the existing plants are requiring more flexibility in accommodating the company's production needs. Home-grown batch application can be very difficult to change to accommodate new products if they didn't follow the ISA-88 philosophy. Extensive programming changes might be required to add new products and procedures. The use of a batch software package up front, even before the flexibility is required, can make this growth much easier in the long run. You can add new recipes without having to touch the control code, saving time and resources.
Improved knowledge management: In life sciences especially, a symbiotic relationship exists between the creator of the application and the machine on which the application runs. The attitude is "I take care of my machine, and my machine takes care of me." This can be very effective, but in such a relationship, the machine settings receive the operator's accumulated knowledge. And as applications grow larger and more complex, the machine can literally crumble beneath the intellectual property the application contains. When it's time to migrate, moving the logic to another system can be a nightmare. If the information structure followed ISA-88 standards, the application logic could continue to advance, regardless of the brand or model of equipment.
Behind the byline
Daren Moffatt is a business development manager in life science at Invensys Systems in Lancaster, Penn.
Batch standard basics
The ISA-SP88 committee writes standards to provide the industry with guidelines to design and specify batch control systems. The committee covers subjects such as defining terminology specific to batch control systems to encourage understanding between manufacturers and users; providing a standard data structure batch control language to simplify programming, configure tasks, and communicate between the various components of the system; and providing a standard data structure to simplify data communications within system architectures.
According to the formal scope of the committee, the physical model is the hierarchical structure that relates control equipment and data communications needed for the physical areas involved in batch control. The functional model shows the relationships between the five types of control: recipe management, scheduling, sequential control, regulatory control, and safety interlock systems.
The ISA-SP88 committee published the first three standards in a series on batch control in industrial automation systems. Subjects include models and terminology for defining the control requirements for batch manufacturing plants, data structures and guidelines for languages, and general and site recipes. The committee is now working on Part 4, which includes information on batch production records.
Better butter with batch software
By Rick Kurio
With stiff competitive pressure from soy manufacturers, Canbra Foods Ltd., a large oilseed crushing, refining, processing, and packaging company in Canada, continues to look for ways to increase manufacturing efficiency and reduce costs. The Lethbridge, Alberta, Canada, facility employees realized the usefulness of structure in the ISA-88 batch standard. Using it has made all the difference in the facility's automation processes, building in efficiency and effectiveness.
Canbra's major products include cooking and salad oil, margarine, shortening, and a full line of proteins. The company markets its products in packaged form to retailers and distributors in the food service industry and in bulk-to-food manufacturers. The production process begins with canola seed cleaning using seed cleaning equipment to remove unwanted matter. The seeds are crushed to extract oil. Finally, the oil runs through a refining process involving a crystallizer machine where it becomes a finished product for packaging. In the refining phase, the oil blends with a custom milk to create margarine products.
While the oil preparation process has been largely automated, the milk-preparation stage was mostly a manual operation. It began with the manual addition of 33-lb bags of salt and 44-lb bags of whey powder into a pre-mixer on an open processing floor. The result was production bottlenecks, spillage, and documentation challenges. The pre-mixer occasionally received inaccurate amounts of ingredients. Worse yet, employees faced potential injury from manually lifting the bags and pouring them into the pre-mixers. Manually activating the mixer and pumps left the process open to human error.
Automation to the rescue
With these challenges in mind, we sought to automate ingredient addition in the milk-preparation phase using batch management software to reduce waste, increase throughput, and eliminate risk of injury.
The facility used to conduct batch programming in a conventional PLC type environment but didn't use a structured batch system following the ISA-88 standard before. Basing changes on the batch standard provides a structured programming format the automation world universally accepted, where Canbra could have various engineers.
We chose an automated batch software package to convey, load, unload, weigh, feed, and process bulk solid material. The software controls all operations of the bulk handling system using programmable controllers with remote I/O located locally on the system. When an operator picks a recipe from batch software that calls for 200 lbs of salt and 300 lbs of whey powder, the controller receives two set points. The software package then directs the bulk-addition system to operate two 15-ft bulk-bag dischargers to dump the whey powder and salt into two eight-cubic-ft-capacity stainless steel hoppers.
From each hopper, a 30-ft-long flexible screw conveyor elevates the ingredient for gravity feeding through two Y-diverter valves. From there, the ingredient transports to one of two mixing tanks. As a bag discharges, load cells transmit weight-loss signals to a controller, which shuts off the flexible screw conveyor once it reaches the set batch weight. The controller passes the data to and from the SCADA system, which also communicates with a controller that governs the system's agitators and pumps.
The greatness of standards
The software is based on the ISA-88 standard. From the batch aspect, it gives everyone a consistent look and feel to the software and PLC. The newfound structure allows for easier trouble shooting. Typically an engineer had a different style of writing programs. That makes it difficult to troubleshoot someone else's program. But the ISA-88 standard gives everyone a consistent program to follow—a consistent structure inside the PLC, so no matter who is going in to trouble shoot, if they know the ISA-88 standard, they'll know where to look for problems.
Also the batch itself provides better use of equipment. It lets you queue up batches so the operator doesn't have to be there to wait for you to start them. By using the standard, the facility relies less on operators initiating starting and stopping batches. It lets operators modify recipes easily without having to go into the PLC and recode everything.
Automating the milk-preparation process with the batch software gave Canbra the ability to minimize production bottlenecks, increase efficiency, and provide a safer work environment. Since automating the process, the company has been able to save $45,000 a year. Using the ISA-88 batch standard, the software collects data on each batch and compiles it into batch records or event logs. This allows management to identify process trends and deviations, as well as efficiently track ingredients for food safety audits.
The company has realized additional savings through increased batch accuracy. What's more, worker safety has improved since workers no longer have to handle 30- to 40-lb bags of material. The success of the new process has prompted Canbra to explore integrating its oil blending system with the milk blending system to streamline the production process further. By incorporating the oil preparation phase into the batch system, the company will have a seamless process for producing margarine products.
Behind the byline
Rick Kurio is a control systems coordinator at Canbra Foods Ltd. in Lethbridge, Alberta, Canada.