Network accessible interface for a process control network

Details Network accessible interface for a process control network Network accessible interface for a process control network

1997-12-30

2001-02-20

Gordon, Paul P. (Department: 2786)

Data processing: generic control systems or specific application

Generic control system, apparatus or process

Plural processors

C700S003000, C700S005000, C700S017000, C700S083000, C709S208000, C709S217000, C710S105000, C710S110000

Reexamination Certificate

active

06192281

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to process control networks and, more specifically, to an interface that communicates data between a process control network having distributed control functions and a remote communications network.
DESCRIPTION OF THE RELATED ART
Large processes such as chemical, petroleum, and other manufacturing and refining processes include numerous field devices disposed at various locations to measure and control parameters of a process to thereby effect control of the process. These field devices may be, for example, sensors such as temperature, pressure, and flow rate sensors as well as control elements such as valves and switches. Historically, the process control industry used manual operations like manually reading level and pressure gauges, turning valve wheels, etc., to operate the measurement and control field devices within a process. Beginning in the 20th century, the process control industry began using local pneumatic control, in which local pneumatic controllers, transmitters, and valve positioners were placed at various locations within a process plant to effect control of certain plant locations. With the emergence of the microprocessor-based distributed control system (DCS) in the 1970's, distributed electronic process control became prevalent in the process control industry.
As is known, a DCS includes an analog or a digital computer, such as a programmable logic controller, connected to numerous electronic monitoring and control devices, such as electronic sensors, transmitters, current-to-pressure transducers, valve positioners, etc. located throughout a process. The DCS computer stores and implements a centralized and, frequently, complex control scheme to effect measurement and control of devices within the process to thereby control process parameters according to some overall control scheme. Usually, however, the control scheme implemented by a DCS is proprietary to the DCS controller manufacturer which, in turn, makes the DCS difficult and expensive to expand, upgrade, reprogram, and service because the DCS provider must become involved in an integral way to perform any of these activities. Furthermore, the equipment that can be used by or connected within any particular DCS may be limited due to the proprietary nature of DCS controller and the fact that a DCS controller provider may not support certain devices or functions of devices manufactured by other vendors.
To overcome some of the problems inherent in the use of proprietary DCSs, the process control industry has developed a number of standard, open communication protocols including, for example, the HART®, PROFIBUS®, WORLDFIP®, Device-Net®, and CAN protocols, which enable field devices made by different manufacturers to be used together within the same process control network. In fact, any field device that conforms to one of these protocols can be used within a process to communicate with and to be controlled by a DCS controller or other controller that supports the protocol, even if that field device is made by a different manufacturer than the manufacturer of the DCS controller.
Moreover, there is now a move within the process control industry to decentralize process control and, thereby, simplify DCS controllers or eliminate the need for DCS controllers to a large extent. Decentralized control is obtained by having field mounted process control devices, such as valve positioners, transmitters, etc. perform one or more process control functions and by then communicating data across a bus structure for use by other process control devices in performing other control functions. To implement these control functions, each process control device includes a microprocessor having the capability to perform a control function as well as the ability to communicate with other process control devices using a standard and open communication protocol. In this manner, field devices made by different manufacturers can be interconnected within a process control network to communicate with one another and to perform one or more process control functions forming a control loop without the intervention of a DCS controller. The all-digital, two-wire bus protocol now being promulgated by the Fieldbus Foundation, known as the FOUNDATION™ Fieldbus (hereinafter “Fieldbus”) protocol is one open communication protocol that allows devices made by different manufacturers to interoperate and communicate with one another via a standard bus to effect decentralized control within a process.
Thus, process control systems have expanded from local communication loops including a number of field devices connected to one or more controllers to large scale communication networks. However, it is currently difficult to transmit field device information on a process control network to other communication networks, perhaps over large distances, to effect, for example, performance analysis, diagnostic testing, maintenance and trouble-shooting and the like. In fact, a satisfactory technique for transferring fundamental-level field device information, such as process control valve data, has not been found. While, transfer of field device information has been attempted using fiber-optic communication between multiple remote process control sites, such a fiber-optic interconnection between sites is expensive and conflicts often arise in when multiple devices attempt to send information at the same time. Furthermore, the fiber-optic systems include complex communication controllers that arbitrate usage of the bus. Because each data transmission of this system is synchronous with the collection of data at the individual field devices, data collection is stalled while waiting for access to the fiber-optic line and communications are stalled while waiting for the collection of data.
Transmission of field data over a network conventionally involves the passing of encapsulated information packets through network-to-network connections (typically, LAN-to-LAN networks). The packets are encapsulated and have transfer parameters added thereto at each node of the network so that the information packets gain additional extraneous information and require processing time at each node. This conventional remote communication technique is slowed by delays at each node and is inefficient due to the addition of extraneous information at each encapsulation.
It is desirable, therefore, to provide a simple interface device that communicates field device data between a process control network and a communication network or other remote sites without requiring the field devices within the process control network to stall operation while waiting for access to the communication network and without requiring unnecessary processing at each node of the network.
SUMMARY OF THE INVENTION
The present invention is directed to an interface device that interfaces between a communications network and a process control network that does not alter the communications occurring in the process control network and that does not require the addition of extraneous data to packets on the communication network. The interface device of the present invention may be formed by a computer executing a software communication protocol associated with, for example, the Fieldbus communication protocol, and a user software layer that processes Fieldbus requests from a single user or multiple users across a local area network (LAN) or a wide area network (WAN). The user software layer provides a direct interface to the Fieldbus communication network in a device to a remote site via a network connection.
In accordance with the present invention, an interface between a communications network and a process control system includes a communication software stack operating in a process control system and interface software including a routine that monitors message traffic on the communication software stack, a routine that copies the message traffic to storage, and a media interface software routine that allows remote access to the storage.
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