Exchanging DCS information with an SAP system involves integrating business systems.
The SAP client/server based R/3 system has generated much interest in the chemical manufacturing industry.
More than 3,000 companies in 36 countries use SAP software of some form. The challenge now facing many chemical companies is the efficient exchange of information, through a robust interface, between an SAP system and the distributed control system (DCS) controlling process plants.
This interface would allow for the real time delivery of recipes from R/3 to the DCS, and the return of process data and events, such as the rapid update of inventory and production information from the DCS to the R/3 system.
This flow of information can be handled by SAP’s production planning for process industries (PP-PI) module.
The R/3 System is composed of application modules. These span the scope of business operations, from financial to logistics to human resources management. It has multiple language and currency capabilities, making it well suited for global information management.
The modules are delivered as an integrated application suite which includes: production planning and control, materials management, plant maintenance, quality assurance, projects, accounting, order entry, shipping, invoicing and personnel management.
The SAP/process interface PP-PI is primarily designed for batch-orientated production in the chemical, pharmaceutical, food and beverage industries, but enhancements are being added to provide improved support for continuous processes.
A master recipe contains the steps required to produce a product or provide a service (i.e. clean-out), using one or more resources and a list of materials.
One of the main uses of the master recipe is for preliminary planning of production processes. The information concerning operations, primary and secondary resources required, material needs, and standard values are all used during this planning phase.
For planning, a group of resources is defined, which can be allocated to a master recipe. Individual resources within this group then need to be identified for a process order.
The order may copy information from a master recipe and modify this information, or data may be entered directly into the process order. The order needs actual values to be entered, which will be used for the production run.
Process instructions are assigned to phases within the master recipe and the process order, and are used to transfer data from the process order/control recipe to the process control level.
The instructions are normally combined into one or more control recipes, and can contain information on individual processing steps, as well as process data needed by process management, other R/3 modules, or control systems.
Control recipes are generated when a process order is released for production. More than one control recipe may be created in an order, depending upon the number of control recipe destinations.
Business integration perks
Process management coordinates the data exchange between PP-PI and the systems involved in process control and quality assurance. It generates and sends control recipes to the control module and receives process messages to be passed to the defined destinations within SAP.
The problems encountered in running a global chemical manufacturing operation are many. Companies struggle with world-wide trends and changes, such as currency shifts, personnel shifts, cultural changes, local legislation, etc.
They have difficulty in figuring out why a plant in one country makes money while a similar plant in another country does not. The information to help these companies is not available in real-time in a manner to provide essential decision support.
By providing a real time interface between the DCS system controlling a process and the SAP R/3 System, a company will have the ability to address all of these problems.
This interface allows a production plant to achieve both vertical and horizontal integration. Integrated planning of the production, transport, and waste disposal data flows of a plant is possible.
The interface will also support the integration of all plants in an enterprise over the entire logistics chain. This occurs vertically by means of an integrated information flow, ranging from central business applications down to the process control in the plant.
Horizontally, this integration is supported by the coordination of planning between production plants, as well as with the recycling and waste disposal facilities and the plant laboratory.
In order to provide an effective interface the control system must be able to provide open access to the control and other real-time data that has been historically considered proprietary and inaccessible outside the control system itself.
Interfacing to PP-PI currently requires that the control system interface be able to use the RFC (remote function call) interface that SAP has developed. Once this capability has been established, the control system interface must use the RFC mechanisms to receive control recipe downloads from PP-PI.
Since the instructions contained in the PP-PI control recipe specify the types of information that needs to be transferred to the control system (i.e. setpoints) or sent back to PP-PI, the control system interface must be capable of processing those instructions, writing the specified information to the control system database, gathering up the specified data from the control system, and then sending it back to PP-PI in Process Messages using the RFC mechanism.
In addition, the control system interface must have the capability to monitor for certain sets of conditions within the control system, as specified by PP-PI Process Data Subscription instructions.
When the specified conditions become true, the interface must be able to transmit information back to the PP-PI in a Process Message.
In addition to data access and communication requirements, the control system interface needs to provide a suite of operational displays that can be used to view and interact with the control recipes, including a way to monitor the contents of the messages that are being transmitted back to PP-PI.
Control system interface requirements include accepting control recipe downloads from PP-PI , executing the instructions, reporting recipe status and accepting and servicing PP-PI requests.
The control system interface runs in a dedicated, server-class computer and is based on a Windows NT platform (i.e. DEC Alpha, Intel, etc.). Windows NT is the initial OS platform selection because: it is an open system, via TCP/IP; it is consistent with computer purchasing trends in process control, and the run-time portion of the control system interface could still be ported to other OS platforms.
SAP’s PP-PI computer connects to the control system interface via Ethernet. The control system interface should provide disk-based message buffering in the event that the link to SAP is down.
All sequential and regulatory control will then be performed in controller-type devices in the process control system. Further, process instructions sheets (PI sheets) will be available for operator interface, either through dedicated PCs or via X-term displays.
Control system interface operational displays (recipe status, debug, schedule, etc.) are available for operator interface, either through dedicated PCs or via X-term displays.
Through the local interface workstation or a window from the operator’s console, the downloaded control recipes can have several actions performed upon them.
* The Authors are with Fisher Rosemount Inc.