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INDUSTRY TRENDS Factory Integration Technologies - (Part 2) |
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Following on from the first part of this article, Part 2 introduces some of the integration technologies used at the Supervisory Control level of an organisation. Part 3 will conclude with the integration technologies used at the MIS level. Supervisory Control IntegrationThe Supervisory Control level integrates three main areas:
In addition to other control functions performed, the Supervisory Control level acts as an intermediate processing stage for control information transferred from the MIS level to the Control System level and vice-versa. For example, production orders received from an MRP system may be further processed at the Supervisory Control level to allocate specific factory resources to each product and create a specific schedule for each production line or machine in the factory. The supervisory control system may also monitor and record production information on a real time basis, transferring summary information back to higher level systems at the completion of an order or batch. One of the most important functions of the Supervisory Control level is to integrate operators and production management with the other control systems in the process. Computer based interfaces are typically used to monitor the system, fine tune process parameters and issue management commands during the production process. Functions typically performed at the Supervisory Level include:
The technologies used to integrate these systems with the Control System level were covered in Part 1 of this article and include OPC (OLE for Process Control) and Ethernet. Integration to the MIS level often involves services provided by the computer environment that the Supervisory Control system runs on. These technologies include standards such as ODBC (Open Database Connectivity), OLE, CORBA, COM and DCOM. These standards are discussed in more detail in Part 3 of this article. The following Sections outline the technologies used to integrate operators at the Supervisory Control level. HMI / SCADA Software SystemsOne of the most common forms of Supervisory Control systems are HMI (Human Machine Interface) and SCADA (Supervisory Control and Data Acquisition) systems. There are literally hundreds of different PC based systems available. However, the more popular systems include:
The operator interfaces in these systems are diagrammatic representations of the process, displayed on a computer monitor. They are dynamically updated with real-time data from the Control System level, with animations and colour used to assist operators to quickly understand the current status of the process. The main features of these systems include:
DCS (Distributed Control Systems)The functions performed by a DCS are very similar to those of a PLC / HMI system. Part of the reason for developing HMI and SCADA systems was to create a low cost equivalent to DCS using PCs and PLCs. The functions of the Control System level and Supervisory Control level are highly integrated in DCS. Historically, the integration technologies between the Control System and Supervisory levels were often proprietary to each DCS vendor and not readily accessible by the end user or third parties. This has changed over time and DCS now generally support standard field busses or Ethernet. There are numerous arguments about the benefit of DCS over PLC/HMI systems and vice-versa. For integration of the operator with the process, however, DCS perform a similar function to HMI/SCADA systems discussed above. Operator Display and Feedback SystemsThe most common form of these systems are large LED displays, mounted in locations visible by most staff in the factory. Systems CSE have been involved with consist of "scoreboards" 3 metres wide by 1.8 metres high. The main part of the scoreboard has 8 lines of data, 60 - 80 characters wide. A single scoreboard can be used in one factory, with multiple scoreboards used where production, packaging and other processes are carried out in different locations throughout the site. The scoreboards can display information such as the planned schedule for the current shift, with real-time updates of production completed and quantity still to finish. The software driving the scoreboards is able to forecast what the current production should be, based on standard production times, and displays the number of units behind or ahead of schedule. Although the display area is limited, the scoreboard can cycle through multiple "pages" of data, with additional management information and operator messages displayed periodically. Scoreboards make the production process visible to all factory staff. Staff can monitor schedules and other critical data and take immediate action when required. POP (Point of Production) TerminalsThese are like personal scoreboards, distributed at locations throughout the factory where information must be displayed to the operator. In contrast to scoreboards, POP terminals can also capture information at the point of production, either by operator entry, or directly from the process. For information entered by operators, the alternative is generally to have operators record information on paper forms for later processing. In some cases, POP terminals are the only practical method of capturing subjective information. POP Terminals can be dedicated mini data terminals or they can be based on small, panel PCs with touch screen interfaces. They are generally connected with host computers running management software using serial or Ethernet networks. PDA's (personal digital assistants) running Windows CE are also beginning to gain popularity for these applications. The availability of low cost, portable hardware, radio based networks and the ability to run standard office applications such as spreadsheets, allow development of complex applications at reasonable cost.
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