Data processing: measuring – calibrating – or testing – Measurement system – Statistical measurement
Reexamination Certificate
2002-12-10
2004-09-28
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Statistical measurement
C700S108000
Reexamination Certificate
active
06799143
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to process control systems. More particularly, the invention related to a process and a device for evaluating the performance of a process-control system.
BACKGROUND OF THE INVENTION
Process control systems are commonly used to control industrial systems such as chemical reactors, distillation columns, pulp digesters, power-generation plants, etc. Innovations in control-system technology, including distributed control systems and programmable logic controllers, have increased the complexity of process control systems used in such applications. Contemporary process control systems can operate with dozens, or in some cases, hundreds of inputs and control loops.
The performance of each individual control loop of a multi-loop process control system needs to be optimized, or “tuned,” to achieve optimum overall performance in the control system. The individual control loops, however, often interact with other control loops. Hence, changes in the performance of one loop (both positive and negative) can adversely affect the performance of other loops in the control system.
The performance of a multi-loop control system typically changes as both the control system and the process being controlled age. For example, pneumatic components of a control system can lose their effectiveness over time due to air leaks, and corrosion on electrical contacts and wiring can degrade the effectiveness of electronic components. Moreover, the above-noted interaction between control loops in a multi-loop system can multiply the adverse effects associated with the degradation of a single control loop.
Performance degradation in a process control system can adversely affect the process being controlled by the system. Hence, the performance of process control systems is often monitored to determine when corrective action such as maintenance, repair, or retuning is needed.
Most current techniques for monitoring the performance of multi-loop process control systems analyze each controlled parameter on an individual basis. In other words, each control loop is usually considered in isolation from the other loops, and a single representation of the overall performance of the system typically is not available. Hence, it can be difficult to monitor the overall performance of the process control system, and to compare the overall performance with a benchmark level to determine when corrective action-such as maintenance or repairs is required. Furthermore, typical monitoring techniques do not account for the effects of different operating conditions on the performance of the individual control loops, or for the relative importance of certain loops with respect to factors such as economic impact.
SUMMARY OF THE INVENTION
A preferred process for evaluating the performance of a process control system at controlling a first and a second process operating parameter of an automated system comprises generating a first set of data comprising a plurality of measurements of the first process operating parameter, generating a second set of data comprising a plurality of measurements of the second process operating parameter, and calculating a first statistical index from the plurality of measurements of the first process operating parameter using a statistical process control method.
A preferred process also comprises calculating a second statistical index from the plurality of measurements of the second process operating parameter using the statistical process control method, scaling the first and second statistical indices based on predetermined characteristics of the first and second process operating parameters, and combining the first and second statistical indices to produce a performance index representative of the performance of the process control system at controlling the first and second process operating parameters.
A preferred process for evaluating the performance of a system comprises sampling data representative of a first and a second parameter controlled by the system, calculating a first and a second statistical index for the respective first and second parameters, scaling the first and second statistical indices based on predetermined characteristics of the first and second parameters, and combining the first and second statistical indices.
A preferred process for evaluating the performance of a process control system comprises generating a first set of data comprising a plurality of measurements of a first parameter controlled by the process control system and generating a second set of data comprising a plurality of measurements of a second parameter controlled by the process control system.
A preferred process also comprises calculating a first statistical index from the first set of data using a statistical process control method, calculating a second statistical index from the second set of data using the statistical process control method, and combining the first and second statistical indices to produce a performance index representative of the performance of the process control system at controlling the first and second parameters.
A preferred process for evaluating the performance of a process control system at controlling a first and a second process operating parameter comprises calculating a first statistical index for the first process operating parameter based on a plurality of measurements of the first process operating parameter, calculating a second statistical index for the second process operating parameter based on a plurality of measurements of the second process operating parameter, scaling the first and second statistical indices based on predetermined characteristics of the first and second process operating parameters, and combining the first and second statistical indices.
Another preferred process for evaluating the performance of a process control system at controlling a first and a second process operating parameter comprises calculating a first statistical index for the first process operating parameter based on a plurality of measurements of the first process operating parameter, calculating a second statistical index for the second process operating parameter based on a plurality of measurements of the second process operating parameter, scaling the first and second statistical indices based on predetermined characteristics of the first and second process operating parameters, and calculating a performance index representative of the performance of the process control system at controlling the first and second process operating parameters based on the scaled first and second statistical indices.
A preferred embodiment of a device for evaluating the performance of a process control system at controlling a first and a second process operating parameter of an automated system comprises an input/output interface for communicating with the process control system, and a central processing unit electrically coupled to the input/output interface. The central processing unit comprises a processor electrically coupled to the input/output interface, a memory-storage device electrically coupled to the processor, and a power supply electrically coupled to the processor and the memory-storage device.
The central processing unit also comprises a set of computer-executable instructions stored on the memory-storage device for generating a first set of data comprising a plurality of measurements of the first process operating parameter, generating a second set of data comprising a plurality of measurements of the second process operating parameter, calculating a first statistical index from the plurality of measurements of the first process operating parameter using a statistical process control method, calculating a second statistical index from the plurality of measurements of the second process operating parameter using the statistical process control method, scaling the first and second statistical indices based on predetermined characteristics of the first and second process operating parameters, and combining the first and second sta
Chaws Roman P.
Frerichs Donald K.
ABB Inc.
Hoff Marc S.
Raymond Edward
Woodcock & Washburn LLP
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