Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
2000-10-02
2004-04-27
Vanderpuye, Kenneth (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S241000
Reexamination Certificate
active
06728262
ABSTRACT:
BACKGROUND
The manufacturing process for virtually every industry has evolved to some level of automation. Computers and computer-controlled machinery now control and monitor almost every aspect of the manufacturing and industrial process. The management of this automation involves elaborate and detailed software platforms targeted to perform industrial or process control. Most companies within the industrial controls market use software referred to as Human Machine Interface (HMI) software. HMI is a generic term describing any software package used to interface process control information with a human operators.
In its basic elements, HMI systems communicate with field controllers and bring data from those controllers into a central database for processing and monitoring. An operator in a single location can then monitor and control the industrial process throughout a facility. HMI systems, therefore, centralize the management and collection of data from field control devices into one location.
Field controller devices are connected to a process control system over a communication network and typically comprise programmable logic controllers (PLCs), which are programmable computing devices used to monitor elements or conditions in plant or machine operation such as temperature, pressure, number of cycles, etc. The PLC itself may comprise a small box with several computer controlled instruments or may comprise a self-contained microcontroller system. A PLC “box” may comprise an oscilloscope functionality, a computer controlled valve, or a simple environmental sensor, such as a thermometer or barometer. PLCs may also generally be used to control various tasks in the overall manufacturing or industrial process such as stopping or starting the flow of material or electricity, diverting flow, or any other such activity. In order to properly manage process control information, HMI systems generally need to have the process control data, which is gathered by the PLCs, transported to the central location of the HMI server. Until recently, much of the process control data was transported over proprietary networks. These are networks provided by field controller manufacturers which supply the PLCs, the network devices, the cabling, the process servers, and the communication format.
Because each proprietary network uses its own communication formats and protocols, manufacturing and industrial facilities are restricted to purchasing all compatible equipment solely from the proprietary network manufacturer. This closed network restriction typically requires the customer to have all software customized to the particular network protocols used by the network manufacturers. Customers also typically maintain programming personnel to develop new device drivers in the proprietary formats in order to maintain compatibility with new equipment or new processes. Without such programming personnel, a customer would have to pay the network manufacturer to develop customer-specific device drivers. Such closed formats cause industrial and manufacturing customers to expend a great deal of money to maintain the network.
Recently, the process controls industry has begun evolving into the use of open architecture networks. One such open architecture network that is beginning to find applications in the process controls industry is Ethernet. Through its business applications, Ethernet has become one of the most popular types of local area networks (LAN) for business or office computer systems. Ethernet is based on carrier sense multiple access/collision detection technology (CSMA/CD). Ethernet devices such as hubs or switches control the data transfer over the network by sensing whether the network is currently in use. If no use is detected, data is allowed to flow through the system. If the system is occupied, the data transfer is held until the system is free. Network devices also detect collisions, which are events caused when two devices attempt to transfer data over the network at the same time. Through this series of collision detection and use sensing, along with priority algorithms for managing collisions, data is quickly and efficiently transmitted between network devices.
One of the main benefits of Ethernet networks for business systems came with the development of 10 Base-T Ethernet technology. The 10 Base-T technology allowed the Ethernet network and information to be transmitted over the regular twisted pair wiring found in most telephone systems. This enables Ethernet networks and LANs to be installed in buildings using the twisted pair wiring already installed for the telephone network. While Ethernet networks may also be constructed with coaxial cable or fiber-optic cable, the twisted pair capability has allowed Ethernet to rise to the level of an industry-standard in office LAN technology.
The data transmission in an Ethernet network derives from the series of network devices such as hubs, switches, and routers. Ethernet hubs are centralized switching units that connect to all of the nodes on the network. Every node connected to the hub transmits its status information to the hub in a standard format, such as simple network management protocol (SNMP). After receiving this information, the hub rebroadcasts it, in SNMP, out to all of the other nodes connected to the hub. In this manner, each device is able to monitor the status and activity of each other device connected to the hub.
While Ethernet grew into an effective business/office LAN standard, the same Ethernet devices could not readily be transported into an industrial controls network. The typically hostile environment on the manufacturing plant floor provides elements, such as extreme temperatures, electrical interference, and continuous vibration, which are generally and desirably not present in an office environment. Ethernet network devices, which were robust enough for the office LAN, would typically experience short life cycles and unreliable performance when exposed to the harsh industrial environment. However, as the industry began recognizing the benefits of the Ethernet standard, companies slowly developed new robust Ethernet devices designed with increased environmental shielding. Thus, the process controls industry began assembling plant and industrial networks using Ethernet technology. Ethernet-based HMI systems and field logic controllers have since been developed for the growing number of process control systems implemented over Ethernet networks. The influx of more suitable Ethernet equipment and compatible software has caused an industry shift toward open architecture networking systems and standardization.
The new Ethernet HMIs basically perform the same function of interfacing the data gathered by the field logic controllers with the human technician. However, with the shift toward open networking, new standardized formats have been developed for communicating process control information within HMI platforms. Based on Microsoft Corporation's OLE technology, a standard called OLE for Process Control (OPC) is being incorporated into more HMI platforms. Working inside of the HMI platform, OPC standardizes the communication of process data obtained from field controllers. While the PLC vendor may still have a proprietary transport protocol, once the information is passed through a system interface, the HMI platform can universally process and internally communicate the data through OPC. In this manner, the HMI system is able to process the information independently from the PLC vendor protocol.
In some industrial applications, excessive pressure or temperature could lead to a catastrophic event causing serious loss of life and/or environmental contamination. These industries in particular have a critical need to monitor the real-time network status to ensure that the real-time process control data received by the HMI system is accurate. Because Ethernet technology became a standard for office LAN systems, many network management software systems exist which monitor network status and performance. Industrial user
COI Software, Inc.
Fulbright & Jaworski L.L.P.
Vanderpuye Kenneth
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