Advances in Control Loop Optimization

There was a time when “control loop optimization” meant selecting the proportional, integral, and derivative tuning parameters for all of the PID controllers in a plant so as to optimize the closed-loop performance of each loop individually. Loop tuning is still a critical element of loop optimization, but thanks to recent advances in control theory and commercial software products,...

05/01/2008


Sidebar:
Loop optimizer products

There was a time when “control loop optimization” meant selecting the proportional, integral, and derivative tuning parameters for all of the PID controllers in a plant so as to optimize the closed-loop performance of each loop individually. Loop tuning is still a critical element of loop optimization, but thanks to recent advances in control theory and commercial software products, the control operations of an entire plant can now be optimized to maximize overall profitability, not just individual loop performance.

As George Buckbee, vice president of marketing and product development for ExperTune puts it, “Control systems personnel are using control loop monitoring and performance supervision software to generate measurable economic benefits. Today’s loop optimization software focuses on providing 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 on the areas where they can make the biggest improvement.” See the chart, “Typical improvements from loop optimization.” (PlantTriage software by ExperTune

Dr. Alireza Haji-Valizadeh, manager of technology development for ControlSoft, adds that today’s loop performance monitoring and diagnostic tools can:

  • Provide both automatic and manual loop tuning and analysis tools;

  • Keep track of all the loops in the plant no matter what platform or vendor;

  • Execute non-intrusive, continuous on-line performance analysis;

  • Generate customizable loop performance indices such as error distribution, integral of absolute error, process variability, and economic impact; and,

  • Disseminate loop performance reports to all levels of the plant’s business hierarchy and across the Web.

Loop maintenance and more

Haji-Valizadeh notes that his company’s InTune software (version 5) offers all of these features as well tools that are capable of addressing maintenance issues such as:

  • How a loop’s performance foreshadows future maintenance requirements;

  • How loop maintenance efforts should be allocated to maximize return on investment;

  • Which of the problem loops have the most room for improvement; and,

  • How to keep loops continuously optimized on a plant-wide scale.

Steve Johansen, global services marketing manager for advanced solutions at Honeywell Process Solutions points to Honeywell’s Loop Scout as a comprehensive loop management workflow solution that contains loop analysis tools, valve diagnostics, a robust control theory-based tuning package, and alternative techniques to PID control.

Loop Scout collects data on process values, setpoints, controller outputs, and control loop configuration data throughout the plant; then generates performance reports for each loop. Expert guidance tools walk the novice user through the data and offers additional tests to determine if there’s a maintenance issue (such as stiction in a valve), a tuning issue, or a problem with the control strategy itself.

“Loop Scout has evolved to the point where the user doesn’t need to understand the underlying technology. He only needs to drill down to the specific information that impacts decision-making. The user can choose which characteristic by which he wants to rank and sort his loops — the severity of each problem detected, the general performance of each loop (good, fair, poor, etc), or the greatest opportunity for improvement in terms of business metrics,” says Johansen.

John Caldwell, DeltaV product marketing manager at Emerson Process Solutions adds that DeltaV InSight is an on-line process modeling tool that automatically learns the process based on normal day-to-day operations then monitors performance, and identifies and diagnoses problem loops; it also recommends tuning and maintenance improvements. He also notes that new developments in adaptive control, advanced diagnostics, and performance reporting are planned for release later this year with DeltaV version 10.3

 


A recent survey conducted by Honeywell Process Solutions suggests that almost one-third of control loops are operating with at least "acceptable" performance.

Better, but not perfect

Whether due to advances in loop optimization technology or other causes, there has been some improvement in control loop performance across the process industries. The average respondent to a 1996 Control Engineering survey reported that approximately 55% of their control loops were running in closed-loop rather than manual or open-loop mode. Of those running in closed loop, 45% were believed to be optimized.

More recently, a survey of PID controllers conducted by Honeywell Process Solutions showed that 64% were operating in closed loop with 50% of those tuned to provide “excellent” or “acceptable” performance. That still leaves a lot of room for improvement, as shown in the chart. Yet, loop optimization tools aren’t always the best way to realize additional controller performance.

Manual tuning needed too

“I once used a commercial loop tuning package and didn’t find it very useful for the particular loop I was trying to tune,” says Matt Lyles, managing partner at SBL Systems, a control system engineering company. He suspects that the significant deadtime in his loop may have been the problem, so he resorted to a tried-and-true manual tuning technique.

“I can see where there could be some critical processes out there where there is limited time allowed to tune a loop and where either a good loop tuner or derivation would be necessitated,” Lyles added. “Typically the loops I have worked with were not critical and allowed me plenty of time and even wasted product to get the loop right.”

Process control consultant Barry Payne of Barry D. Payne & Associates also has mixed feeling about loop management software. “We have found that tuning software is useful if the control loop it is applied to is functioning properly, and the person using the software already understands what a 'normal response’ is for the process.

“If the loop is subject to significant unmeasured disturbances while the tuning software is being used, or if one or more of the end devices is malfunctioning, then the tuning software (at least that supplied by a few of the larger DCS manufacturers) may give unpredictable and frequently erroneous results.”

He cites an example where a DCS-based automatic loop tuner failed to recognize that the very low model gain it had determined for a particular process was due to an instrument malfunction rather than the actual process dynamics. “Anyone with experience tuning this type of simple loop would have quickly recognized that there was a fault. Auto-tuning software can be useful, but only when used in combination with experience in tuning a particular type of application. It is not an 'Easy button’ for those with little or no skill at loop tuning and troubleshooting.”

Benefit

Typical range

Conservative range

Source: Control Engineering with data from ExperTune

Energy reduction

0.5% to 2%

0.5% to 1%

Production increase

1 to 10%

1 to 2%

Valve maintenance budget

10% to 50% reduction

10% to 20%

Quality improvement

5% to 50% improvement

5% to 10%

ROI from performance supervision

3 to 9 months

1 to 2 years


Vance VanDoren is consulting editor to Control Engineering. Reach him at controleng@msn.com .




Loop optimizer products

Loop optimizing software is available from a wide variety of sources. Some are designed to be universal, and some for specific control platforms.

PlantTriage by ExperTune

Software

RSLoop Optimizer from Rockwell Automation

Optimization tools analyze and tune PID loops in Allen-Bradley PLC-5, SLC 500, and Logix controllers to reduce process variability, improve productivity, and maximize efficiency.

PCS 7 PID Tuner from Siemens Energy & Automation

An option for the Siemens PCS 7 distributed control system helps users determine the optimum tuning parameters in defined steps for PID, PI and P control loops.

Optimize IT Loop Performance Manager from ABB

Software tools help control engineers and process operators start-up, diagnose and maintain control loops on ABB and competitors’ systems.

Control Performance Monitor from Matrikon

A condition-based application monitors, identifies, diagnoses and remedies control asset issues across all plants layers and offers monitoring, tuning and modeling capabilities within one platform.

Windows Servo Design Kit from Galil Motion Control

Software uses a closed-loop frequency response test to generate PID parameters that optimize the performance of Galil motion control systems.

Automation Studio from B&R Automation

Auto-tuning function optimally configures the controller for an Acopos multi-drive system and allows expert users to custom tune individual control loops.

PI Control Monitor from OSIsoft

Four basic measurements– process variable, setpoint, controller output, and on/off control flag - are monitored to alert operations personnel when a control system is in trouble.

ControlWizard and TuneWizard from Plant Automation Services

ControlWizard provides non-invasive identification of control problems, detects poor control loop performance, troubleshoots problems, targets maintenance efforts, and improves product quality. TuneWizard provides data acquisition, process and control valve diagnostics, process identification, controller tuning, control loop simulation and report writing.

BESTune from BESTune.com

Software determines if the plant’s PID loops are optimally tuned and how large the potential benefits might be to retune them.

ControlMonitor, Model ID and PID Tuning from Control Arts

ControlMonitor automates the task of determining which loops need attention, delivering detailed reports on which loops aren’t performing and how to fix the problem. The Model ID and PID Tuning packages generate dynamic models of the process and quickly calculate the best PID parameters from a few simple plant tests.

Control Loop Assistant from Lambda Controls

Process control optimization tools include loop tuning software, data acquisition hardware and data analysis software.

Loop-Pro Software

A suite of software modules provide PID controller tuning, data analysis an modeling, and control loop strategy design, simulation, and training.

Aprom from PiControl Solutions Co.

Online software calculates more than 25 performance criteria per control loop then generates a single “grade” factor between 0 and 100 to indicate overall loop performance.

Pitops-PID from Artcon Inc.

Process Identification and Controller Tuning Optimizer Simulator tunes all PID loops from millisecond time frame to several hours of time constant.

Protuner from Techmation

Hardware and software system records and analyzes dynamic test data in order to troubleshoot, tune, and optimize single-loop and complex multivariable regulatory control systems.

TOPAS from ACT

Software allows users to develop, tune, optimize and troubleshoot basic and advanced control loops to produce better performance in a shorter time.

Tune-Plus from Givens Control Engineering

Tuner analyzes bump test data and recommends loop tuning parameters based on the Lambda tuning method and the user’s specification on control speed.

Loop-Pro Product Suite from Control Station

Intuitive process modeling and tuning modules simplify PID control so users can optimize plant operations and improve the performance of business-critical processes.

U-Tune PID Tuning package from Contek Systems Ltd.

Tuning algorithms account for excessive noise and disturbances and give the process control engineer direct input into the process identification phase.



No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2013 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
The true cost of lubrication: Three keys to consider when evaluating oils; Plant Engineering Lubrication Guide; 11 ways to protect bearing assets; Is lubrication part of your KPIs?
Contract maintenance: 5 ways to keep things humming while keeping an eye on costs; Pneumatic systems; Energy monitoring; The sixth 'S' is safety
Transport your data: Supply chain information critical to operational excellence; High-voltage faults; Portable cooling; Safety automation isn't automatic
Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Plant Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.

Maintaining low data center PUE; Using eco mode in UPS systems; Commissioning electrical and power systems; Exploring dc power distribution alternatives
Synchronizing industrial Ethernet networks; Selecting protocol conversion gateways; Integrating HMIs with PLCs and PACs
Why manufacturers need to see energy in a different light: Current approaches to energy management yield quick savings, but leave plant managers searching for ways of improving on those early gains.

Annual Salary Survey

Participate in the 2013 Salary Survey

In a year when manufacturing continued to lead the economic rebound, it makes sense that plant manager bonuses rebounded. Plant Engineering’s annual Salary Survey shows both wages and bonuses rose in 2012 after a retreat the year before.

Average salary across all job titles for plant floor management rose 3.5% to $95,446, and bonus compensation jumped to $15,162, a 4.2% increase from the 2010 level and double the 2011 total, which showed a sharp drop in bonus.

2012 Salary Survey Analysis

2012 Salary Survey Results

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.