Advances in Control Loop Optimization

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Advances in Control Loop Optimization


Software takes users from simple tuning to plant
-
wide
optimization.

Vance VanDoren, Ph.D., P.E. Control Engineering
--

Control
Engineering, 5/1/2008


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 plan
t
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 p
lant 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 an
d
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

identif
ies,
diagnoses, and prioritizes improvement opportunities according to economics.)

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 distribu
tion,
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 I
nTune software (version 5) offers all of these
features as well tools that are capable of addressing maintenance issues such as:

Sidebar:

Loop optimizer products





How a loop’s performance foreshadows future maintenance requirements;



How loop maintenance efforts should be allocated to maxi
mize 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 collec
ts 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, e
tc), 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 lear
ns 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
diagnostic
s, and performance reporting are planned for release later this year with
DeltaV version 10.3

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 controll
ers
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

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


Extend that to a minimum of at least
"fair," and you cross the half
-
way point.


Of course
there is
still that 36% running in manual.

of room for improvement, as shown in the chart. Yet, loop optimiz
ation 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, mana
ging 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 pr
ocesses 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 wast
ed 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 functionin
g 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 m
alfunctioning, 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
-
tuni
ng 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 ra
nge

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












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

identifies, diagnoses, and prioritizes

improvement opportunities according to
economics. Connects to any DCS using OPC. Provides KPIs, reports, alerts, and
dashboards with drill
-
down capability to solve root
-
cause issues and is fully integrated
with loop tuning and analysis tools.
www.planttriage.com

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 maxim
ize
efficiency.
www.ab.com

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.
www.sea.siemens.com/process

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.
www.abb.com

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.
www.matrikon.com

Windows Servo Design Kit from Galil Motion Control

Software uses a closed
-
loop frequency response test to generate PID parameters that
optimize t
he performance of Galil motion control systems.
www.galilmc.com

Automation Studio from B&R Automation

Auto
-
tuning function optimally configures the controller for an Acopos multi
-
drive
system and allows expert users t
o custom tune individual control loops.
www.br
-
automation.com

PI Control Monitor from OSIsoft

Four basic measurements


process variable, setpoint, controller output, and on/off
control flag
-

are monitored to a
lert operations personnel when a control system is in
trouble.
www.osisoft.com

ControlWizard and TuneWizard from Plant Automation Services

ControlWizard provides non
-
invasive identification of control problems, detect
s 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 simulat
ion and
report writing.
www.pas.com

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.
www.bestune.isclever.com

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
p
roblem. 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.
www.controlartsinc.com

Control Loop Assistant fro
m Lambda Controls

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

Loop
-
Pro Software from Control Station Inc.

A suit
e of software modules provide PID controller tuning, data analysis an modeling,
and control loop strategy design, simulation, and training.
www.controlstation.com

Aprom from PiControl Solutions Co.

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

Pitops
-
PID from Ar
tcon Inc.

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

Protuner from Techmat
ion

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.
www.protuner.com

TOPAS from ACT

S
oftware allows users to develop, tune, optimize and troubleshoot basic and advanced
control loops to produce better performance in a shorter time.
www.act
-
control.com

Tune
-
Plus from Givens Control Engineering

Tune
r analyzes bump test data and recommends loop tuning parameters based on the
Lambda tuning method and the user’s specification on control speed.
www.givenscontrol.com

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.
www.controlstation.com

U
-
Tune PID Tuning pac
kage 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.
www.contek
-
systems.co.uk