Plant-wide automation at Elgiloy Specialty Metals. Background of project. Process utilization and efficiency. Production scheduling and monitoring, страница 4

The real-time process controllers operating in the rolling mill and on the other plant processes are as follows:

·  Sequencing and interlocking — Simatic® S5 PLCs.

·  Loop controllers and communication — Simadyn® D controllers.

Network addresses have been arranged such that traffic conflicts are minimized Elgiloy has been assigned a single Class C network address for the corporation. However, network address translation (NAT) with subnetting is utilized to realize a series of Class C networks within the facility. The IP addressing assignment for these local area network (LAN) segments has been chosen to minimize transmission collisions. For instance, it can be seen that a network bridge has been inserted to isolate the rolling mill system and the other process controllers from the remainder of the plant network. All addresses in this LAN segment share the same Class C assignment and only traffic destined for the MSC system will traverse the bridge. All of the other network branches connected to the CISCO switch are also configured as separate ethernet LAN segments. Hence, there are distinct network segments within the plant for the following:

·  NT workstations located at all the process lines.

·  Shipping and receiving area workstations.

·  MSC server and WSS workstation.   

·  Level 2 rolling mill system.

·  Process controllers.

When considering information flow and data availability, it was decided that information gathered at each process, as well as plant product scheduling information, should be visible to all of the individual operations. Hence, a central database for the entire plant was the optimum choice. This database resides in the MSC system server, shown in Fig. 2. All processes within the plant are connected to this central database, which then serves the various man-machine interface (MMI) screens used by the operators. The rolling mill contains a separate database and MMI for control purposes. Rolling mill data are transferred to the MSC database, discussed in detail under rolling mill automation. Operators at the other process lines, production planning staff and the shipping and receiving departments all have access to the plant-wide data. Each of the lines is supplied with unique operating MMI screens, which display relevant data for that particular process. These screens are operated from the appropriate NT workstation. Additionally, production staff can use various screens to create work orders and schedule coils to work orders, as well as alter other coil information. Operators responsible for running the process lines are able to enter coil data and other information as each coil is processed.

The database for the MSC system is a relational database and was designed using advanced CASE tools. These design tools allow a structured analysis from a functional and data point of view to be performed, which results in an entity relationship model. The basis for this analysis is typically a functional description or specification detailing the requirements of the system. Once the entity relationship diagrams have been created, they serve two fundamental purposes. First, they are the basis for the physical database table layout with all dependencies, imparting referential integrity to the database. This allows obsolete data to be eliminated from the database once they are no longer used without leaving orphaned table entries, which are no longer connected to physical coils. The second purpose of the CASE tool is to provide a convenient and permanent documentation for system design.

Process utilization and efficiency

Production planning for the plant is handled at corporate headquarters, where all enterprise resource management is performed. At this location, ESM has a special application for planning production at the Elgiloy plant and other corporate facilities. The production planning system (PPS) application runs on a platform that also contains a relational database into which the customer orders are placed by a separate task. The objective of the PPS is to create work orders which satisfy the customer orders and can be ultimately scheduled and processed at the Elgiloy facility. These work orders are comprised of groups of customer orders with similar characteristics such as target thickness and width, alloy, target tensile strength and target surface quality.