The design and commissioning of the controls associated with a continuous or batch process directly impact plant operating efficiency and production quality and throughput. In this session we review techniques that may be used to identify control opportunities to reduce production costs, minimize variations in product quality and to maximize production within the limits set by market demand. Several common application examples from the process industry will be used to illustrate how plant production rate and product quality are directly influenced by process control variation and constraints in plant operation. Starting with an assessment of control loop utilization and automatic control performance, a step by step process is outlined that may be used to identifying and addressing areas where it is possible to justified the time and material costs required to improve control performance. In particular, information will be provided on how to quickly tune single loop control of self-regulating or integrating process and to recognize when variations in control loop performance are not associated with loop tuning. An overview will be provided of tools and techniques that may be used to achieve best control performance over a wide variety of operating conditions. Also, guidance will be provided on when it is possible to justify the cost associated with the installation and commissioning of multi-loop techniques such as feedforward control, ratio and override control. The steps required to commission multi-loop control strategies will be address along with common mistakes to avoid. Also, input will be provided on how to recognize when advanced control techniques such as Fuzzy logic or MPC are needed to achieve the desired control performance. At the end of this session a drawing will be held to give away 10 copies of “Control Loop Foundation – Batch and Continuous Processes”. Many of the ideas discussed in this session are addressed in this book.

1. Maximizing the Return on
Your Control Investment
Part 1 of 2
Meet the Experts Sessions

2. Presenters
 James Beall
 Terry Blevins

3. Session Objective
 Provide a roadmap that may be used to maximize the
return on your control investment

4. Agenda
 Assessment of control loop utilization and automatic
control performance,
 Identifying areas where it is possible to justified the
cost of improving control performance.
 Tools and techniques to achieve best control
performance. Identifying and correcting field
problems.

5. Evaluating Control System Utilization
 Product quality and
manufacturing efficiency
may be impacted by
variation in key
parameters.
 When production is
process limited, then
throughput may be
increase by reducing
process variation and
operating closer to the limit.
 The control must operate
as designed to achieve
these benefits.

6. Control Utilization
Control utilization is an indicator that can be used to
quickly determine if control and measurement problems
exist within a control system. Surveys indicate that the
primary reasons for control not being fully utilized fall
into two areas:
 Field measurement or control element
 Process or control design
An immediate improvement in control utilization will be
achieved by addressing these problems. To achieve full
utilization, improved communications between
maintenance and operations is important.

7. Example – Case Study
At one pulp and paper plant a snapshot of the control utilization was
collected to quantify the state of the process control. This survey showed:
Control Normal
Loops Mode Utilization
Bleach Plant 78 60 76%
Power House 185 130 70%
Pulp Mill 174 116 66%
Paper Mill 236 134 56%
An instrumentation team was formed to investigate loops that were not
running in their normal design mode. This team was responsible for making
sure measurement, control valve, and process problems were addressed in
a timely fashion. The reduction in variability led to significant improvements
in plant throughput and product quality

8. Example – Another Case Study
At refinery and petrochemical complex a snapshot of the control utilization
was collected to quantify the state of the process control. This survey
showed:
System Loops Utilization
PX 471 67.3%
APS&VPS、CLE、Sulfur Recovery 469 59.7%
Refinery 478 60.9%
IGCCAuxiliary Boiler 946 52.7%
Ethylene 1355 77.5%
FCCU 475 48%
C4 164 68.9%

9. Examining Control Utilization
 Summarizes performance for System
or by Area, Cell, or Units
 Abnormal Control Conditions
indicated for Problem Loops:
– Control Service Status:
• Not in Normal mode
• Limited control output
• Bad/Uncertain input
– Control Performance Status:
• Standard Deviation
• Variability Index
• Oscillation Index
• Tuning Index

10. DeltaV InSight Control Performance Reports

11. Roadmap to Improved Control
Transmitter Broken/Unreliable Fix or Replace
Transmitter
Reason? Tuning
Poor Valve/Actuator Problem
Investigate
Performance Changing Process Gain
Process Dynamics
No Loop Interaction
Starting
Point Control Loop
in Normal
Mode?
Yes Use DeltaV Insight
to examine loop
tuning
Use DeltaV Insight
to Determine
Control Utilization

12. DeltaV Insight – On-demand Tuning
 Allows
control loop
tuning to be
quickly
established

13. Examine Tuning Impact

14. DeltaV InSight - Adaptive Tuning
Provides Tuning Based on Normal Operator Changes
 InSight automatically
calculates dynamic
Before vs. After
models from
operator changes
 Model Quality and
Learning Status
 Tuning criteria and
desired speed of
response
 Tuning
Recommendation
 No Testing Required

15. Tips for Using On-Demand Tuning
 Set step size large enough to insure the response to
the PID output changing is larger that the
measurement noise and influence of process
disturbances.
 Select “Integrating” if the process is not self-
regulating.
 If the process has low or high gain, then selected
Default Process and set the process type to match
the expected behavior.

16. Manual Tuning (Not a DeltaV System)
 When commissioning PID control associated with a self-regulating
process, this procedure may be quickly applied to both old and new
control systems to determine the tuning for PI control.
 The size of the step should be just large enough to easily distinguish
the resulting change in the controlled process output.

17. Manual Tuning - (Not a DeltaV System)
Alternate
 When commissioning PID control associated with a self-regulating
process, this procedure may be quickly applied to both old and new
control systems to determine the tuning for PI control.
 The size of the step should be just large enough to easily distinguish
the resulting change in the controlled process output.
 Tune as follows:
– Place the PV and OUT on a trend.
– Place the controller in Manual and allow the process to reach steady sate.
– Impose a step change in OUT and observe the response
– Set the RESET equal to ¼ of the time it takes to “almost” line out (98% of final
value)
– Set the GAIN equal to 1/3 of process gain, Kp where
– Kp = ((Δ%PV) / (Δ%OUT) (Be sure to convert to % of span!)
– Place the loop in automatic and make small adjustments to the Setpoint and
observe the response. Adjust ONLY the GAIN to achieve the desired response.

18. Impact of Sticky Valve
 When a control loop is
placed in automatic
Setpoint (SP)
control, it is easy to
detect if a valve or
Controlled Parameter (PV)
damper is not
responding to the
Implied Valve Position (OUT)
Value
control system by
observing the
Stem Position)
response of the
controlled parameter
to control system
Time
changes in the PID
output.
 Cycling can not be
eliminated through
tuning.

19. Valve Positioner Recommendation
The most common problems in commissioning a control system
can often be traced to the fact that a positioner has not been
provided with the valve, or the positioner provided with the valve
has not been properly installed or has malfunctioned.
– The rule of thumb is that to achieve best control
performance, all regulating valves should be equipped
with a positioner.
– Without a positioner, the control performance that may be
achieved is very limited when a valve is sticking – which is
inherent in most valves.
– The cyclic behavior caused by a sticky valve (with no
positioner) cannot be eliminated through tuning. Changes in
tuning will only impact the period of the cycle that develops.
The only way to eliminate this type of behavior is to install a
valve positioner.

20. Installed Characteristics.
7000  From a control perspective, it is
highly desirable that the process
6000 gain be constant. If the process
gain is constant, then the same
5000 proportional gain may be used
over the entire operating range of
Gas Flow (SCFH)
4000 the control loop.
 If the valve characteristic was not
3000 been selected based on the
process requirements, then the
2000 installed characteristic could be
non-linear.
0
 As illustrated in this example, the
0 20 40 60 80 100
Valve Position (%)
process gain varies from 0.5 to 4;
that is, the process gain changes
by a factor of eight.

21. Impact of Non-linear Installed Characteristics
Non-linear Process Example
 Process gain and dynamics may change as a function of
operating conditions such as valve position or feed rate.

22. Linearizing Response
 To compensate for
the changes in
process gain, a
characterizer block
may be installed
between the PID and
Analog Output
blocks. Select the
option to inverse the
calculation done in
the forward path for
the PID back
calculation to allow
bumpless transfer.

23. Characterizer Setup
 The relationship between
Characterizer
100 IN OUT the primary inputs and the
Linear Relationship 0 0
90
Characterizer In-Out
5 1.5 output of the characterizer
10 3
80 15
20
5.5
8,5
block may be defined by
70 25
30
10
11.5
21 x,y pairs over the final
60 35
40
13
17
control element operating
50 45 20
range.
Process Output (%)
50 22
40 55 26
30
60
65
31
36
 Input values that fall
20
70
75
42
48
between these points are
10
80
85
54
63
automatically determined
0
90
95
74
86 by the characterizer block
100 100
using linear interpolation.
 The curve defined by the
characterizer points
0 10 20 30 40 50 60 70 80 90 100 appears as the inverse of
Valve Position (%) the plot of the final control
element installed
characteristic.
Figure 12-8

24. Identifying Model - DeltaV InSight
Gain Process Insight with Model Analysis
 Last 200 Models
automatically stored
for each control loop
in a model database
 Various plot options
to analyze impact of
operating conditions
on process models
 Average of selected
models may be
utilized to establish
the recommended
tuning

25. Non-linear Process Models

26. DeltaV InSight – Adaptive Control

27. DeltaV InSight – Adaptive Control
Adaptive Control Enabled

28. Split Range Control
 One of the most common
ways of addressing multiple
process inputs is known as
split-range control.
 The splitter block may be
used to define a fixed
relationship between the
controller output and each
manipulated process input –
appearing as one valve to the
PID block
 The setup must account for
the gain associated with
each process input to
achieve consistent control
behavior.

29. Example – Steam Header Pressure
 To allow the plant to continue operation if the turbine or generator fails
and must be shut down, pressure reducing valves (PRVs) between the
high pressure header and the lower pressure header may be adjusted
to meet the lower pressure header steam demand and to maintain the
header pressure constant.
 This may be accomplished by using a splitter block in conjunction with
a PID block to adjust the pressure reducing valves.

30. Steam Header – Splitter Characterization
 If the valve sizes or operating conditions for the valves are different, then it is
necessary to characterize the splitter to compensate for these differences.
 For example, if the flow ratings in thousand of pounds per hour, KPPH, of the
valves used in split-range control were as shown below:
– Valve 1 flow rating = 50 KPPH
– Valve 2 flow rating = 150 KPPH
 Then the controller output range of adjustment associated with Valve 1 would
be:

31. Interactive Loops
C1
 The fighting between
M2
C2 interactive loops is most
M2
often addressed by
simply detuning one of
Flow the control loops by
Controller
reducing the proportional
C1 gain.
Composition
Controller M1  The valve associated
Outlet Flow
with the detuned loop
Feed
Valve(M1)
Mixing
(C1) will change very slowly.
C2
Additive
Valve(M2)
Process
Composition Thus, the two loops will
(C2) M1
tend not to interact but at
the expense of the
detuned loop having
slow response.

32. Roadmap to Improved Control
Transmitter Broken/Unreliable Fix or Replace
Transmitter
Reason? Tuning
Poor Valve/Actuator Problem
Investigate
Performance Changing Process Gain
Split range Setup incorrect
No Process Dynamics
Loop Interaction
Starting
Point
Normal
Mode?
Determine Yes Low/acceptable Monitor for
Control Change
Utilization Variation
on Control High
Changing Process Gain
Investigate Process Disturbance
Unacceptable
Process Dynamics
Loop Interaction
Changing Limit Condition

33. Utilize Process Capacity to Absorb Variability
Step change in load (inflow) Outflow = inflow
Controller Output
changing outflow
PV Back to SP in
smoothly!
PV 6 x Lambda
Change in Setpoint LIC
PV stopped
Lambda
Inflow
Outflow

34. Utilize Process Capacity to Absorb
Variability
 Choose the arrest time “slow” enough to
provide a variability sink yet maintain level
within the allowable variation
 Lambda = __2 * ALV___
Kp * MLD
– ALV = Allowable Level Variation
– Kp = Integrating process gain
– MLD = Maximum Load Disturbance (converted
to % of level controller output scale)

35. Utilize Process Capacity to Absorb Variability
Before After
Level
Level
Manipulated
Variable Manipulated
Variable

36. Reducing Control Variation
When tuning is not sufficient to achieved the desired
level of variation in critical control parameter or to
maintain it at an operating limit, then multi-loop
techniques may sometimes be applied to improve
control. Three common multi-loop techniques are:
 Feedforward Control
 Cascade Control
 Override Control

37. Summary
 An on-line measurement of control utilization and
variability is provided by DeltaV Insight.
 Exploring the causes of poor utilization is the first
step in resolving measurement, actuator or control
issues.
 When single loop control is not sufficient to achieve
the desired level of control the multi-loops solutions
should be explored.

38. Where To Get More Information
 Many of the ideas discussed in this session are
addressed “Control Loop Foundation – Batch and
Continuous Processes”. Information on this book
may be found at the book’s web site:
– http://controlloopfoundation.com/
Also, by going to this web site you can use your web
browser to perform the 19 workshops that go with
this book.