Data processing: measuring – calibrating – or testing – Measurement system – History logging or time stamping
Reexamination Certificate
2001-05-31
2004-07-06
Khatri, Anil (Department: 2121)
Data processing: measuring, calibrating, or testing
Measurement system
History logging or time stamping
C700S002000, C700S286000, C702S176000
Reexamination Certificate
active
06760687
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to process control systems and, more particularly, to detecting, storing and reporting the sequence of detectable events occurring within a process control system.
DESCRIPTION OF THE RELATED ART
Process control systems, like those used in chemical, petroleum or other processes, typically include one or more process controllers communicatively coupled to at least one host or operator workstation and to one or more field devices via analog, digital or combined analog/digital buses. The field devices, which may be, for example valves, valve positioners, switches and transmitters (e.g., temperature, pressure and flow rate sensors), perform functions within the process plant such as opening or closing valves and measuring process parameters. The process controllers receive signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices, use this information to implement control routines and then generate control signals which are sent over the buses to the field devices to control the operation of the process. Information from the field devices and the controllers is typically made available to one or more applications executed by the operator workstation to enable an operator to perform any desired function with respect to the process, such as viewing the current state of the process, modifying the operation of the process, etc.
In the past, conventional field devices were used to send and receive analog (e.g., 4 to 20 milliamp) signals to and from the process controllers via an analog bus or analog lines. These 4 to 20 milliamp signals were limited in nature in that they were indicative of measurements made by the device or of control signals generated by the controller required to control the operation of the device. However, in the past decade or so, smart field devices including a microprocessor and a memory have become prevalent in the process control industry. In addition to performing a primary function within the process, smart field devices store data pertaining to the device, communicate with the controller and/or other devices in a digital or combined digital and analog format, and perform secondary tasks such as self-calibration, identification, diagnostics, etc. A number of standard and open smart device communication protocols such as the HART®), PROFIBUS®, WORLDFIP®V, Device-Net®, and CAN protocols, have been developed to enable smart field devices made by different manufacturers to be used together within the same process control network.
Moreover, there has been a move within the process control industry to decentralize process control functions. For example, the all-digital, two-wire bus protocol promulgated by the Fieldbus Foundation, known as the FOUNDATION™ Fieldbus (hereinafter “Fieldbus”) protocol uses function blocks located in different field devices to perform control operations previously performed within a centralized controller. In particular, each Fieldbus field device is capable of including and executing one or more function blocks, each of which receives inputs from and/or provides outputs to other function blocks (either within the same device or within different devices), and performs some process control operation, such as measuring or detecting a process parameter, controlling a device or performing a control operation, such as implementing a proportional-derivative-integral (PID) control routine. The different function blocks within a process control system are configured to communicate with each other (e.g., over a bus) to form one or more process control loops, the individual operations of which are spread throughout the process and are, thus, decentralized.
Furthermore, in many process plants, signals associated with significant events, such as signals associated with the position of certain safety switches or shutdown valves, signals indicating an overflow or underflow detected by certain sensors, signals associated with the operation of important power generation or control devices, signals from fault detection devices or other binary on-off type signals associated with devices within the plant are monitored to detect changes in these signals and to thereby detect “events” within the process plant. The time at which these monitored events occur are recorded and stored in a sequence of events database for use in, for example, debugging the system after a failure or other significant operational situation has occurred.
The use of a sequence of events (SOE) database is beneficial because the occurrence of one event, such as the failure of a device or a communication channel, may cause other events to occur, which may cause still other events to occur eventually leading to, for example, a cascading complete or partial shutdown of the process control plant. To ascertain the ultimate source of the failure in an attempt to correct the problem, a maintenance or control operator may view the sequence of events log stored within the SOE database to determine which events occurred in what order so as to ascertain the precipitating cause of the failure within the system.
The use of sequence of events reporting is common and fairly straight forward in a system having only one node or having a single controller attached to devices through one sequence of events SOE input/output (P/O) detection card, as all the monitored event information passes through the same SOE card and controller. However, in a process control system having a single controller coupled to multiple SOE cards, or in a system having multiple controllers at different nodes, each of which is connected to one or more devices via one or more SOE cards, sequence of events reporting becomes more difficult because the controllers and each of the different SOE cards must be time synchronized to accurately record the order of different events occurring in different parts of the plant. If the controllers or the SOE cards are out of time synchronization, the time information in the sequence of events log is likely to be incorrect which may lead the events being sequenced in an improper order. Further, because the multiple events resulting in a significant event, such as a failure of a node, typically occur very rapidly, e.g., within ten milliseconds of each other, it is desirable to increase the time sensitivity of the sequence of events reporting to the order of five milliseconds be able to detect the actual order in which the different monitored events occur. Generally speaking, this time sensitivity has been very difficult to obtain without highly accurate or synchronized clocks at each SOE card. Unfortunately, it can be prohibitively expensive to place an accurate and stable clock in each SOE card and it can be very difficult to accurately time synchronize many clocks in the system in order to time stamp events when these events are detected at the SOE cards.
SUMMARY OF THE INVENTION
A sequence of events detection system and method for use in a process control network uses SOE cards to automatically detect and store indications of events and the times at which these events took place within the process control network. The sequence of events reporting system includes a stable master time source, such as a global positioning system (GPS) receiver which is used to periodically time synchronize clocks within each of the nodes of the system, such as within each of the controllers, user workstations, etc. Free running counters, such as quartz counters, are located within each controller and within each SOE card being used to detect events to be stored in the sequence of events log. These free running counters are used to mark each event with a counter value when the SOE card or controller first detects the event. Indications of the event and of the counter value associated with a detected event are sent to a corresponding controller (if need be), which uses its clock, its counter and an indication of the value of the SOE counter assigned to the event to ascertain the actua
Apel Michael D.
Bennett William E.
Beoughter Ken J.
Dienstbier Steve
Sokolova Marina
Fisher-Rosemount Systems Inc.
Hartman Jr. Ronald D
Khatri Anil
Marshall & Gerstein & Borun LLP
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