Data processing: measuring – calibrating – or testing – Measurement system – Remote supervisory monitoring
Reexamination Certificate
1998-06-25
2001-09-04
Shah, Kamini (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Remote supervisory monitoring
C702S182000
Reexamination Certificate
active
06285966
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to process control networks and, more specifically, to a method of and to an apparatus for viewing data in a process control network having distributed control functions.
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 the 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®, LONWORKS®, 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 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 capable of performing one or more control functions as well as communicating 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.
As noted above, the decentralization of process control functions simplifies and, in some cases, eliminates the necessity of a proprietary DCS controller which, in turn, reduces the need of a process operator to rely on the manufacturer of the DCS controller to change or upgrade a control scheme implemented by the DCS controller. However, decentralized control also makes it more difficult to compile and view real time values of process parameters at a central location for the field devices. Thus, although the processing control functions of the process operator are reduced or simplified in this decentralized control scheme, it is still desirable to monitor the current operating conditions in the process control network at a central or single location.
In a standard DCS environment and in many distributed control environments, real time information is accumulated by a host device by making information requests to the field devices. When the process operator wants to view the current value of one or more process parameters, the host device creates request messages for the field devices that store the parameters selected by the operator. The request messages are transmitted from the host device on the bus to the field devices. Upon receiving the request messages, the field devices create response messages that are transmitted back to the host device on the bus. Accordingly, each transfer of process parameters from a field device to a host device involves two bus transactions: an information request message and a response message.
In many instances, the process control parameters requested from the field devices by the host are parameters that are otherwise transmitted from one field device to another field device using a separate bus transaction. In each of these instances, three separate bus transactions related to the same information are transmitted along the bus. Additionally, the host monitors information from many field devices so that a large volume of bus traffic is generated by the monitoring operation. The large amount of bus traffic resulting from the monitoring operation can reduce the communication throughput of other important communication operations, possibly reducing the overall responsiveness of the process control network.
A bus monitor is one type of known device that accumulates data without necessitating additional bus traffic in a DCS environment. Bus monitors have no capability to talk or issue requests on the bus, but they constantly listen to the bus and capture all bus transactions that are generated on the bus segment to which they are attached. Presently known bus monitors are designed to monitor the bus traffic and to evaluate the performance of the communication protocol and the bus network. The bus monitors are not intended to be used to monitor process data and, therefore, have only limited capabilities to filter, sort and store process data. For example, a bus monitor may be configured to filter and store all messages of a particular protocol message type, such as all request messages or all response messages, but the monitor cannot extract, store or manipulate the process data contained within the filtered messages. In order to view particular process data, a separate device is required to extract, sort and manipulate the information stored in the bus monitor. Therefore, the bus monitors as presently implemented in DC S environments do not readily provide access to the current operating conditions in the process-control network.
SUMMARY OF THE INVENTION
The present invention is directed to a m
Brown Larry K.
Burns Harry A.
Larson Brent H.
Fisher Controls International Inc.
Marshall O'Toole Gerstein Murray & Borun
Shah Kamini
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