Data processing: generic control systems or specific application – Generic control system – apparatus or process – Having protection or reliability feature
Reexamination Certificate
1997-12-30
2002-04-23
Grant, William (Department: 2786)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Having protection or reliability feature
C700S083000, C714S738000, C714S739000, C714S742000, C714S014000
Reexamination Certificate
active
06377859
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to process control networks and, more specifically, to a maintenance interface device operating 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 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.
However, in the evolution of technology to more advanced solutions such as the trend from analog communication protocols to digital communication protocols, issues or problems are raised in addition to the advantages achieved. For example, in conventional communication systems utilizing analog communications, a fundamental level of trouble-shooting and analysis is possible using simple test devices such as inexpensive digital voltmeters or multimeters that test the conductivity of a circuit under test. As communication systems have evolved towards digital communications, an analysis of the functionality of digital devices and communication lines is achieved only using expensive and unwieldy test devices including logic analyzers and communication systems because the conductivity in digital devices and communication lines measured by conventional voltmeters and multimeters may be excellent while the digital signal indicative of a device failure remains undetected.
In the harsh environment of, for example, oil and gas pipelines, nuclear power generating stations or factories, gaining access to a control valve or other device is often difficult. Finding an electrical outlet is often even more daunting. It is desirable, therefore, to use a simple apparatus and technique for performing a fundamental analysis of the functionality of peripheral field devices connected within a process control system in which communications follow a digital communication protocol.
SUMMARY OF THE INVENTION.
The present invention is directed to a maintenance interface device for use in a digital, loop-powered process control network that includes an interface to either a two-wire inputloutput port of a field device or to a two-wire communication media, control logic that determines a simple status of the field device or communication loop, and a display that displays the status. The maintenance interface device may be used in fault analysis to detect whether a field device is operational or nonoperational.
In accordance with one aspect of the present invention, a maintenance interface device for use in a digital, loop-powered process control network determines whether a device or communication media is operational or nonoperational, whether a device or communication media is powered or unpowered, and whether a device or communication media generates or carries a valid digital signal or an invalid signal. The maintenance interface device is adapted to perform simple functionality tests on a plurality of devices in a process control network including a loop controller, a digital control system, an operator console, a workstation, a personal computer, and a bridge to detect functionality of devices on a bus.
In accordance with another aspect of the present invention, a maintenance interface device for use in a digital, loop-powered process control network is alternatively self-powered (typically using battery power), is powered by the device under service or is powered from the two-wire loop-powered media.
Many advantages are achieved by the described maintenance interface device and operating method. For example, the maintenance interface device is portable and powered either from the two-wire media, the device under test or a battery making the maintenance interface device useable in inhospitable or inconvenient environments where power is otherwise unavailable.
REFERENCES:
patent: 4271505 (1981-06-01), Menot et al.
patent: 4403297 (1983-09-01), Tivy
patent: 4627045 (1986-12-01), Olson et al.
patent: 4691328 (1987-09-01), Sterling, Jr. et al.
Brown Larry K.
Burns Harry A.
Larson Brent H.
Fisher Controls International Inc.
Grant William
Marc McDieunel
Marshall O'Toole Gerstein Murray & Borun
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