Control loop tuning strategies are critical to optimizing plant performance, often giving companies the edge they need to compete favorably in a global economy. However, applying loop optimization properly is not easy. For many engineers, the techniques are academic, involving higher mathematics and complicated theory.
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Control loop tuning strategies are critical to optimizing plant performance, often giving companies the edge they need to compete favorably in a global economy. However, applying loop optimization properly is not easy. For many engineers, the techniques are academic, involving higher mathematics and complicated theory.
Because of the popularity of loop optimization topics, Control Engineering and Reed Corporate Research recently investigated availability, features, and purchasing habits of those involved in specifying, recommending, and/or purchasing control loop optimization software or services (LOS) by conducting their first survey on this topic. Of 310 online respondents, the majority (69%) purchased LOSs for in-plant requirements. Use for both in-plant and OEM requirements accounted for 13%. OEM (resale) requirements made up 18% of the total. Within these results, possible applications for LOSs fell into several categories, including continuous processing, batch processing, combined continuous and batch processing, discrete manufacturing, and utilities services.
According to the survey, the largest numbers of applications were in continuous and batch processing. Respondents also indicated that LOS was used in discrete manufacturing and utility operations but in smaller numbers. Discrete manufacturers and utility services can, in fact, use process control in their facilities. For example, most automotive plant manufacturing would be discrete, but the operation would also include process control applications using PID loops that require optimization in the powerhouse, painting, and electrical departments.
Alireza Haji-Valizadeh, Ph.D, vice president, technology development for ControlSoft Inc., cites gas pipeline pumping stations and water/wastewater facilities as two examples of utility services that use LOS. “The pipelines use basic PID loops that need to be tuned based on the changing flow. Water/wastewater facilities use basic PID loops and more advanced process control (APC) on long dead-time applications, such as chlorination stations. We have been approached by our current water/wastewater customers, in those facilities that use our PID tuning software and APC, to test out our process improvement strategy. This is a good indicator to us that there is much more process control at these facilities and not just discrete control.”
Choices, choices
When control engineers seek outside help or services for control loop optimization, the survey found they choose from among several options. Process automation software vendors’ services provided the majority (44%) of the total responses; 29% listed automation system integrators’ services as their choice. Add-on software vendors’ services made up 14% of the responses, and consulting firm services accounted for 13%.
Control loop optimization is a particularly complex technology that requires extensive manual calculations or highly specialized software. Even the most advanced software depends on the expertise of the user to provide the necessary data and interpret the results. According to Vance VanDoren, Ph.D, president of VanDoren Industries Inc., this complexity plays a large role in the vendor-selection process.
“I would expect the most accomplished users to be the engineers who sell the software, so it makes sense that control engineers who engage outside services for control loop optimization would favor the subject matter experts—the process automation software vendors. I would have expected add-on software vendors to come in a close second, ahead of automation system integrators. Some system integrators are certainly adept at loop optimization, but they’re not necessarily experts with any particular software package,” says VanDoren.
| Most respondents (69%) purchases LOSs for in-plant applications. The largest number (44%) turns to process automation vendors for software and services. |
Looking to the future, as new or upgraded factories enter the planning stage, opportunities exist to change control hardware and the software systems that optimize their overall control functions. However, large, existing facilities rarely have that chance. Even though VanDoren may like to see it otherwise, he feels purchasing trends are unlikely to change. “Process automation vendors’ familiarity with their own software creates an almost unbeatable advantage,” he adds.
Importance of cost
The survey revealed that control engineers have strong preferences when it comes to getting outside help or services for specifying, recommending, and/or buying LOS. By a margin of 2 to 1, potential users chose a vendor for its software. The features they rated as very important include (most important first):
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Ability to integrate with an existing control system;
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Ease of use;
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No shutdown requirement to apply optimization;
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Ability to save money compared to operations before optimization;
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Training included;
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Updates included in purchase;
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Ability to categorize which loops require the most attention;
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Return on investment quantified in economic terms, beyond engineering values;
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Ability to run continuously in the background; and
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Related services included with purchase.
The top five entries garnered the most response. Although those responding felt that all of these features would be nice to have, integration with existing systems, ease of use, no shutdown requirements, money savings, and inclusion of training indicate that lowest total installed cost is a major issue in specifying LOS. However, overall performance also is of high importance.
George Buckbee, director of product development at ExperTune Inc., recommends prospective users consider other factors when considering integrating loop optimization software into their application. “These features include the ability to improve the process, not just the control loop; the ability to customize key performance indices, reports and alerts, and graphical displays; integrated software to allow solving problems; the ability to address the complete loop (sensors, valves, nonlinearities, etc.), not just tuning; and the ability to handle special control issues, such as pH, level control, cascade, MPC, and feedforward,” he says, adding that “the software or software services provider should also have a proven track record in the user’s industry.”
Purchasing trends should show net growth over the next 12 months, the survey finds. When asked about future product purchasing, 23% expected to increase purchases, 19% expected to decrease purchases, and 58% felt requirements would remain the same.
A necessary commodity
The average respondent reported that approximately 55% of their control loops were running in closed-loop rather than manual or open-loop configuration. Of those running in closed-loop configuration, 45% were believed to be optimized. With that many control loops in questionable tune, LOS should be a necessary addition to the control engineer’s arsenal of production optimization tools.
According to Buckbee, “Industry leaders are using control loop monitoring/performance supervision software to get results that are far beyond their competition. Software design and performance are critical to generating these economic benefits. Quality loop optimization software should focus on meaningful, actionable metrics that deliver results to the bottom-line and graphical tools to focus the users’ attention on the most economically important issues, thereby helping them to focus their time and effort to the areas where they can make the biggest improvement. As users learn more about how software can drive bottom-line results at their plants, there will be more clamor for the right features.”
Maximize loop performance
DeltaV Tune offers quick, easy loop tuning for increased control performance and improved economics. Features include sophisticated analysis and simulation tools for the advanced uses. Software is integrated with a plant’s DeltaV system with no communications setup required and has recently been enhanced to include FOUNDATION Fieldbus capability. Included with every Emerson Process ProfessionalPlus station, DeltaV Tune provides out-of-the box tuning solutions for PID and fuzzy logic control loops. Based on a patented, field-proven algorithm for calculating control loop parameters, it can minimize the time required to establish stable, responsive control loops. www.emersonprocess.com
Emerson Process Management
Optimize control loop tuning
PCS 7 PID Tuner helps optimize the tuning of PID control loops running in the Siemens PCS 7 distributed control system. It runs in loop, manual, or automatic modes and optimizes loops with or without an integral component. The tool is tightly integrated into the standard PCS 7 engineering environment. Tuner is activated by highlighting a function block when viewing the configuration in an online mode, launching a wizard-based interface that automatically guides the user through the setup and saves recorded information to a recallable file. www.siemens.com Siemens Energy & Automation
Using a workflow approach
Designed for instrument/electrical technicians and non-Ph.D-level control engineers, Loop Scout software suite monitors control systems, detects and prioritizes problems, proactively notifies appropriate personnel to take action, and intelligently diagnoses and resolves root causes. Workflow approach is said to augment intuitive control loop, alarm, and system diagnostics with notification, reporting, and resolution tools focused on empowering the existing staff to systematically increase plant profitability and reduce operating costs. Loop Scout and control engineering teams combine in a workshop environment to identify and resolve control loop problems, giving the Loop Scout team an opportunity to observe, develop, and refine maintenance best practices with customer interaction through the entire process. www.honeywell.com Honeywell Inc.
Tracking performance, economics
MDPro software developed by Shell Global Solutions and marketed by Shell and Yokogawa Corp. of America includes online monitoring and automatic reporting of single and multivariable control systems. Off-line features focus on diagnostics and analysis and include a tuning function for analyzing PID loops. Diagnostic tools include closed-loop speed of response, minimum error variance, percent uptime, percent in service, percent compliance, and a calculation of the price of nonconformance. It also can track the economic benefits of profit variables. www.us.yokogawa.com Yokogawa Corp. of America
Combined monitoring, loop optimization
Intune v.5 plant management and process control predictive maintenance tool combines process control monitoring with powerful diagnostic and PID loop tuning/optimization tools, including comprehensive statistical analysis; automatic, adaptive, model-based, and offline tuning; customized scripting for plant-specific indices; and Web-based reporting and event notification customized for engineers, operators, and managers. Users can champion their process control strategy based on a wide array of criteria, including energy reduction, increasing productivity, making more consistent product quality to sell, increasing plant engineering productivity, and supporting continuous improvement. www.controlsoftinc.com ControlSoft Inc.
Plant-wide process control
PlantTriage plant-wide performance supervision system optimizes existing process control systems, including operations, equipment, and controls. Using economic information, process context, and real-time data from each control loop, the software reportedly finds the biggest opportunities to improve plant performance. PlantTriage highlights setpoint changes that can save energy and raw materials costs. Web client feature makes plant performance data visible to anyone in the company. Fully customizable reporting and subscription tools ensure that each user sees the data they wish to see, when they want to see it, in the format they want. Detailed loop analysis is accomplished through tight integration with its developer’s PID Loop Optimizer. Using Web-based dashboards, users can view performance at whatever level they wish, from the corporation to individual control loops. www.expertune.com ExperTune Inc.
Control loop management services
Loop management services include comprehensive on-line control loop/control valve diagnostics and reporting, expert loop tuning, and continuous remote monitoring to help maximize control loop performance over time. It is available for Foxboro’s I/A Series automation systems and other vendors’ process control systems. Service includes an evaluation of all current plant or unit control loops using best-in-class diagnostic software tools and comprehensive on-line diagnostics of all control valves. Loop and valve diagnostics are performed using models created from a combination of real-time data and historical information (collected via OPC). This service is available for virtually all process control systems and all field devices. Critical under-performing loops are prioritized for remediation, and if desired, Invensys can perform the actual loop tuning and recommend appropriate valve maintenance activities. Ongoing remote monitoring, reporting, prioritization and on-site remediation services are available to help ensure optimal loop performance over time. www.invensys.com Invensys Process Systems
Low-cost tuning package
Topas is said to be the most comprehensive toolset available for control developmentand controller tuning, optimization, and troubleshooting. Running underMicrosoft Windows, its functions include process parameter estimation (from open- orclosed-loop tests or operating data), performance analysis, and troubleshooting aids that include demonstrations, a glossary, and examples. Recently expanded PID-Tuner module evaluates 25 tuning methods and presents the three best results graphically. It covers self-regulating, integrating processes, and liquid level; users can opt for setpoint or load tuning for best performance, smoothest control action, or minimum resource consumption. Results can be tested and refined within the integrated simulation environment for better coping with noise, sticking valves, process non-linearity, or changing dynamics. www.act-control.com ACT Gmbh
Optimize PID control systems
Loop-Pro Product Suite supports rapid optimization of PID control systems. Engineer users with a highly intuitive process modeling and tuning module said to be ideal for quick, consistent PID controller tuning. Module follows a “recipe-based approach” to enable users to validate the tuning process graphically at each step and tailor the process’ response to achieve objective control performance. Off-line analysis tool can read any flat text file from its users’ DCS or OPC server and provide tunings that are customized to the user’s unique control system and assures accurate, quick, and safe computation of the manufacturer’s control algorithm. It also provides a complete matrix of tuning parameters for P, PI, PID, and PID with Filter. Advanced modeling and tuning capabilities are included. Other modules include Developer, which supports rapid simulation of a user’s process and the evaluation of new control architecture to assure optimal process performance and OPC Inbox, enabling users to access process data and evaluate loop performance in real time. www.controlstation.com Control Station Inc.
Adaptive control method
Model-Free Adaptive (MFA) control is a patented adaptive control method that does not require process models. A MFA control system is defined to have the following properties: precise quantitative knowledge of the process is not necessary; process identification mechanism or identifier is not included in the system; controller design for a specific process is not needed; manual tuning of controller parameters is not required; and closed-loop system stability analysis and criteria are available to guarantee system stability. Once installed, system requires no controller parameter tuning under various operating conditions changes. It is said to be easy to install, use, and maintain. It requires no time-consuming model training, can be launched at any time, and, will start to control the process right away. With no process models inside the controller, the MFA controller can be programmed to run at a very high speed. www.cybosoft.com CyboSoft, General Cybernation Group Inc.
Asset performance control
ProcessDoctor Online continuously monitors control assets in real time and provides a unified platform for detecting and correcting performance problems from instrumentation and regulatory controllers to analyzers, inferentials, and advanced process control applications, regardless of vendor. It includes a set of tools to benchmark current control performance against industry standards; identify and prioritize problems to focus maintenance resources; analyze and diagnose problems with online and offline reports; improve control performance with tools for regulatory and advanced controllers, and sustain improvements with comprehensive, automated reporting. www.matrikon.com Matrikon Inc.
Loop optimization platform
ControlWizard and TuneWizard solutions provide a platform for loop optimization, including an automated on-line performance assessment and monitoring tool and an off-line control loop tuning and analysis package. ControlWizard automatically collects real-time or historical data from any control system or data source via OPC or other connectivity protocols. Data are then analyzed to establish control loop performance metrics and rank control loop performance using any combination of 70+ different analytical techniques, as configured by the user. TuneWizard provides a tuning and “what-if” performance analysis environment in which the control engineer can test various control loop settings for robustness and performance. Features include hierarchical representation of data in a tree map for performance visualization, correlation of index, and performance parameters for user analysis, and comment fields to record plant state and user comments. www.pas.com PAS Inc.
Monitoring control loops
Control Monitor software, as part of its developer’s RtPM platform, helps users monitor standard metrics that identify the quality parameters of process control loops. Software is said to take the guesswork out of quality measurements, allowing users to focus on turning real-time data into long-term process improvements, and informs them of the control loops requiring immediate attention. Use of Control Monitor for loop optimization is said to ensure control system performance by monitoring predetermined quality measurements and their deviations and evaluating control loop statistics, displaying the results of this evaluation in the RtPM platform’s key process visualization tool, ProcessBook, so that the manager, process operator, or instrument technician can check the system’s current status. It also produces a daily report listing as exceptions those control loops that need attention. www.osisoft.com OSIsoft Inc.
Related reading
Loop Controllers: Lone Logic is More Connected
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