Process control 4 chapter

Advanced Process Control
Systems
19AEI-406.51 & 52

29AEI-406.51 & 52
• Introduction to control system configuration
• Single variable control system
• Independent Variable control system
• Interactive Variable control system
• Compound Variable control system

39AEI-406.51 & 52
Single Variable
• The elementary process-control loop is a single-variable
loop.
• The loop is designed to maintain control of a given
process variable by manipulation of a controlling
variable, regardless of the other process parameters

49AEI-406.51 & 52
Independent Single Variable
• In many process-control applications, certain regulations
are required regardless of other parameters in the
process.
• In these cases, a set point is established, controller
action is started, and the system is left alone

59AEI-406.51 & 52
Independent Single Variable…
• As shown in the figure.1, a flow control system is used to
regulate flow into a tank at a fixed rate determined by the
set point.
• This system then makes adjustments in valve positions
as necessary following a load change to maintain flow
rate at the set point value.

69AEI-406.51 & 52
Two variable process control loops that interact
Figure.1

79AEI-406.51 & 52
Interactive Single Variable
• A second single variable control loop, is shown in the
figure, regulates the temperature of liquid in the tank by
adjustment of heat input.
• This is also a single-variable loop that maintains the
liquid temperature at the set point value.
• Under normal conditions, the flow into the tank is held
constant and the temperature is also held constant, both
at their respective set point values.

89AEI-406.51 & 52
Interactive Single Variable…
• However, a change in the set point of the flow-control
system appears as a load to the temperature-control
system, because the fluid level in the tank or rate of
passage through the tank must change.
• The temperature system now responds by resetting the
heat flux to accommodate the new load and bring the
temperature back to the set point

99AEI-406.51 & 52
Interactive Single Variable…
• Thus we see that these two loops interact.
• Almost any process where several variables are under
control shows such interactive behavior.
• Any cycling or other instability of the flow-control loop
causes cycling in the temperature system because of
this interaction

109AEI-406.51 & 52
Compound Variable
• In some cases, a single process control loop is used to
provide control of the relationship between two or more
variables.
• This can be accomplished by using measurements from,
say, two sensors as input to the process controller.

119AEI-406.51 & 52
Compound Variable…
• A signal-conditioning system must scale the two
measurements and add them prior to input to the
controller for evaluation and action.
• The analysis of such systems can become quite
complicated

129AEI-406.51 & 52
• A common example is when the ratio of two reactants
must be controlled.
• In this case, one of the flow rates is measured but
allowed to float (not regulated), and the other is both
measured and adjusted to provide the specified constant
ratio.

139AEI-406.51 & 52
• An example of this system is shown in the figure.2.
• The flow rate of reactant A is measured and added, with
appropriate scaling, to the measurement of flow rate B.
• The controller reacts to the resulting input signal by
adjustment of the control valve in the reactant B input
line.

149AEI-406.51 & 52
A compound system for which the ratio of two flow
rates is controlled Figure.2

Multivariable Control
AEI-406.5315

AEI-406.5316
• Any complex industrial process is multivariable because
many variable exits in the process and must be
regulated.
• Many of these are either non interacting or interaction is
not a serious problem in maintaining the desired control
functions.

AEI-406.5317
• In such cases, either single-variable controls or cascade
loops sufficient to effect satisfactory control of the overall
process.
• Then multivariable refers to those processes wherein
many strongly interacting variables are involved.

AEI-406.5318
• Such a multivariable system can have such a complex
interaction pattern that the adjustment of a single set
point causes a profound influence on many other control
loops in the process.
• In some cases, instabilities, cycling, or even runaway
result from the indiscriminate adjustment of a few set
points.

AEI-406.5319
SISO
• The control configurations we have examined so far
were confined to processes with a single controlled
output, requiring a single manipulated input.
• Such single input, single output (SISO) systems are very
simple.

AEI-406.5320
MIMO
• Chemical processes usually have two or more controlled
outputs, requiring two or more manipulated variables.
• The design of control systems for such multiple input,
multiple output (MIMO) is complex and requires fairly
good knowledge of the process.
• A MIMO controller can recognize and compensate for
process interaction much more effectively than can
standard SISO controllers on individuals loops.

AEI-406.5321
Multivariable Control (MVC)
The problems in MVC
• It is important to select the proper variable pairing for
interactive feedback control.
• Application of feed forward compensation is desirable
to help minimize the required effort of interactive
feedback loops reacting to process disturbance.

AEI-406.5322
• The use of selective or override controls where
possible will minimize the need for interactive feedback
loops.
• Using interaction compensation will frequently help to
provide a stabilizing effect on interactive feedback
loops and allow tighter tuning.

AEI-406.5323
Analog Control
• When analog control loops are used in multivariable
systems, a carefully prepared instructional set must be
provided to the process personnel regarding the
procedure for adjustment of set points.
• Generally, such adjustments are carried out in small
increments to avoid instabilities that may result from
large changes

AEI-406.5324
Analog Control…
• Consider a situation where there is a reaction vessel in
which two reactants are mixed, react, and the product is
drawn from the bottom.
• We are now concerned with controlling the reaction rate.

AEI-406.5325
Analog Control…
• It is also important to keep the reaction temperature and
vessel pressure below certain limits, and finally, the level
is to be controlled at some nominal value.
• If the reactions are exothermic-that is, self-sustaining
and heat-producing- then the relation among all of these
parameters can be critical.

AEI-406.5326
Analog Control…
• If the temperature is low, then an indiscriminate increase
in steam-flow set point could cause an unstable runaway
of the reaction.
• Therefore, in this case, the level and reaction flow rates
must be altered as the steam-flow rate is increased to
maintain control.

AEI-406.5327
Analog Control…
• The necessary steps are empirically determined or from
numerical solutions of complicated control equations.

AEI-406.5328
Supervisory and Direct digital Control
• The computer is ideally suited to the Supervisory and
Direct Digital Control problem presented by the
multivariable control system.
• The computer can make any adjustments of system
operating points in an incremental fashion, according to
a predetermined sequence, while monitoring process
parameters for interactive effects.

AEI-406.5329
SUPERVISORY CONTROL

AEI-406.5330
Supervisory and Direct digital Control…
• The problem in such a system is determining the
algorithm that the computer must follow to provide the
control function of set point sequence.
• In some cases control equations are used.
• In complex interactions, these relations are not
analytically known.

AEI-406.5331
• In some cases, self adapting algorithms are used,
causing the computer to sequence through a set of
operations and letting the result of one operation
determine the next operation.
• As an example, if the temperature is slightly raised and
the pressure rises, then the drop the temperature and so
on.

AEI-406.5332
• The computer can sequence through micro adjustments
of set points looking for the optimum adjustment path.

Cascade Control System
9AEI-406.5633

9AEI-406.5634
Applications
• Cascade control systems are used in
• Evaporator controls
• Heat exchanger controls
• pH control systems

9AEI-406.5635
Applications…
• Distillation control
• Stirred- tank reactors
• Refrigeration control system
• Temperature control system

9AEI-406.5636
Jacketed SCTR
• Consider the CSTR shown in Fig. 3.16.
• The reaction is exothermic and the heat generated is
removed by the coolant, which flows in the jacket
around the tank.

9AEI-406.5637
• The control objective is to keep the temperature of the
reacting mixture, T, constant at a desired value.
• Possible disturbances to the reactor include the
• Feed temperature Ti
• Coolant temperature Tc.
• The only manipulated variable is the
• Coolant flow rate. Fc.

9AEI-406.5639
Simple feedback control
• The control configuration shown in Fig. 3.16 (a) is for
simple feedback control.
• It is clear that T will respond much faster to changes in
Ti than to changes in Tc.
• Therefore, the simple feedback control will be very
effective in compensating for changes in Ti and less
effective in compensating for changes in Tc.

9AEI-406.5641
Cascade Control
• We can improve the response of the simple feedback
control to changes in the coolant temperature by
measuring Tc and taking control action before its effect
has been felt by the reacting mixture.
• Thus, if Tc goes up, increase the flow rate of the coolant
to remove the same amount of heat.
• Decrease the coolant flow rate when Tc decreases.

9AEI-406.5642
• Two control loops using two different measurements, T
and Tc, but sharing common manipulated variable, Fc.
• How these loops are related is shown in Fig. 3.16 (b).
The loop that measures T (controlled variable) is the
dominant, or primary, or master control loop and uses a
set point supplied by the operator.
• Whereas the loop that measures Tc, uses the output of
the primary controller as its set point and is called the
secondary or slave loop.

9AEI-406.5643
Liquid level control in a tank
• Consider the problem of controlling the level of liquid in a
tank through regulation of the input flow rate.
• A single variable system to accomplish the control is
shown in Fig. 3.17(a).
• A level measurement is used to adjust a flow control
valve as a final control element.
• The set point to the controller establishes the desired
level.

9AEI-406.5645
• In this system, upstream load changes cause changes in
the flow rate that result in level changes.
• The level change is, however, a second stage effect
here.
• Consequently, the system cannot respond until the level
has actually been changed by the flow rate change.

9AEI-406.5647
• Fig. 3.17(b) shows the same control problem solved by a
cascade system.
• The flow loop is a single variable system as described
earlier, but the set point is determined by a
measurement of level.
• Upstream load changes are never seen in t

489AEI-406.57 & 58
FEED FORWARD CONTROL
• The feed forward control configuration react to
variations in disturbance variables (set point), predict
the disturbance’s effects and take corrective action to
eliminate its impact on the process output.
• The feed forward controllers have the theoretical
potential for perfect control.

499AEI-406.57 & 58
• But, it is difficult to measure all possible disturbance
variables.
• And to predict their effect effect quantitatively, feed
forward control is generally used along with feedback
control.

509AEI-406.57 & 58
STRUCTURE OF FEEDFORWARD
CONTROL
• It measures the disturbance
directly
• And then it anticipates the
effect that it will have on the
process o/p.
• Subsequently it changes
the manipulated variable by
such an amount as to
eliminate completely the
impact of the disturbance
on the controlled o/p.
PROCESS
CONTROLLER
disturbances
M.V
Controlled
o/p

519AEI-406.57 & 58
STRUCTURE OF FEEDFORWARD
CONTROL
• Control action starts
immediately after a change in
the disturbance has been
detected.
• That the feed back acts ‘after
the fact’, in a compensatory
manner,
• Whereas feed forward acts
‘beforehand’ in an
anticipatory manner.
controller
process
disturbances
M.V Controlled
o/p
51

529AEI-406.57 & 58
Applications
• Heat Exchanger
• Boiler drum level control
• Distillation column
• Continuous stirred tank reactor

539AEI-406.57 & 58
EXAMPLE OF FEEDFORWARD CONTROL
(STIRRED TANK HEATER)
• Consider the stirred tank heater
• The control objective is to keep the
temperature of the liquid in the tank at a
set point.
• Feed back loop ,It measures the
temperature in the tank and after
comparing it with the desired value,
• It increases or decreases the steam
pressure,
• Thus providing more or less heat into the
liquid.
Fig: STIRRED TANK HEATER

549AEI-406.57 & 58
EXAMPLE OF FEEDFORWARD CONTROL
(STIRRED TANK HEATER)
• A feed forward control system used a
different approach as shown in fig.
• It measures the temperature of the inlet
stream (disturbance) and adjusts
appropriately the steam pressure
(manipulated variable).
• Thus it increases the steam pressure if
the inlet temperature decreases.
• And decreases the stream pressure
when the inlet temperature increases.
steem
Fig: STIRRED TANK HEATER

559AEI-406.57 & 58
Feed Forward with Feed Back control
• In most cases a combination of feed forward and feed
back techniques can correct the process deviation in the
shortest time.
• Feed forward loops are usually corrected by feedback
trimming.
• With feed forward ,the feedback control must only
change its output by an amount equal to the feed
forward system fail to correct

569AEI-406.57 & 58
FEEDFORWARD CONTROL OF VARIOUS
PROCESSING UNITS (1.HEAT EXCHANGER)
• The object is to keep the exit temp. of
the liquid constant by manipulation the
steam pressure.
• There are two principal disturbances
(loads) that are measured for feed
forward control.
• Liquid flow rate & liquid inlet
temperature.
• Feed forward control can be developed
for more than one disturbance also.
• The controller acts according to which
disturbance changed value. Fig: HEAT EXCHANGER
56

579AEI-406.57 & 58
FEEDFORWARD CONTROL OF VARIOUS
PROCESSING UNITS (1.HEAT EXCHANGER)
• This fig. represents the general
case of feed forward control with
several loads (disturbances) and a
single controlled variable.
• The major components of load are
entered into a model to calculate
the value of the manipulated
variable required to maintain
control at the set point.
Fig: FEED FORWARD CONTROL LOOP
57

589AEI-406.57 & 58
BOILER DRUM LEVEL CONTROL
• Heat the objective is to keep the
liquid level in the drum constant.
• The two disturbances are the steam
flow from the boiler,
• Which is dictated by varying demand
elsewhere in the plant,
• And the flow of the feed water which
is also the principal manipulated
variable.
Fig: DRUM BOILER

599AEI-406.57 & 58
Advantages
• Good for slow systems (Multicapacity system).
• Act before effect of a disturbance has been felt by the
system.
• Good for significant dead time systems.

609AEI-406.57 & 58
Disadvantages
• More costly
• Require more engineering efforts
• Sensitive to process parameter variations

619AEI-406.59
FEEDFORWARD-FEEDBACK CONTROL
Feed forward control has the potential for perfect
control, but it also suffers from several inherent
weaknesses as listed below:
• It requires the identification of all possible
disturbances and their direct measurements,
• Something that may not be possible for many
processes.
61

629AEI-406.59
• Any changes in the parameters of a process cannot be
compensated by a feed forward controller because
their impact cannot be detected.
• Feed forward control requires a very good model for
the process, which is not possible for many systems in
industry.

639AEI-406.59
ADVANTAGES & DISADVANTAGES OF
FEEDFORWARD CONTROL
ADVANTAGES
1. Acts before the effect of a
disturbance has been felt by
the system.
2. Is good for slow systems or
with significant dead time.
3. It does not introduce
instability in the closed loop
response.
DISADVANTAGES
1. Requires identification of all
possible disturbances and
their direct measurement.
2. Cannot cope with
unmeasured disturbances.
3. Sensitive to process
parameter variations.
63

649AEI-406.59
ADVANTAGES & DISADVANTAGES OF
FEEDBACK CONTROL
ADVANTAGES
1. It does not require
identification & measurement
of any disturbance.
2. It is insensitive to modeling
errors.
3. It is insensitive to parameter
changes.
DISADVANTAGES
1. It waits until the effect of the
disturbances has been felt by
the system before control
action is taken.
2. It is unsatisfactory for slow
processes or with significant
dead time.
3. It may creates instability in the
closed-loop response

659AEI-406.61 & 62
• It is convenient method of controlling variables
maintaining a fixed relation among them.
• A single process control is used to provide The
relationship between two or more variables.
Characteristics of Ratio Control

669AEI-406.61 & 62
• It can be accomplished by using measurement from two
sensors as input to the controller.
• Before evaluation of inputs, a signal conditioning system
must scale the two measurements and add them.

679AEI-406.61 & 62
r
b
cx1
x2
controller process x1/x2
Ratio control

689AEI-406.61 & 62
• In this system c = x1/x2
• x1 & x2 = measured variables of process
• Either one of variable can be held uncontrolled
• Other is varied as required for the optimum control

699AEI-406.61 & 62
• Ratio of two reactants (variables) must be controlled.
• One of the flow rates is measured & allowed to float (not
regulated).
• Other is both measured & adjusted to provide the specific
constant ratio.

709AEI-406.61 & 62
• Flow rate of reactant A is measured and added with
appropriate scaling to the measurement of flow rate B
• Two variables
• Flow rate of A
• Flow rate of B
General Example

719AEI-406.61 & 62
A compound system for which ratio of two flow
rates is controlled

729AEI-406.61 & 62
• Floating variable
• Flow rate of A
• Flow rate A is measured, but uncontrolled
• Adjusting variable
• Flow rate B
• Flow rate B is both measured & controlled

739AEI-406.61 & 62
1. Consider an acid-water ratio control system which
automatically controls the addition of fresh acid in correct
proportion to the water used. this system regards &
integrates the consumption of both water & acid.
Example

749AEI-406.61 & 62
• It simplifies the control of solution level as the operator
adjusts only the water valve
• Ratio factor is set by a ratio relay (or) multiplying unit
• Located between flow transmitter & flow controller
set point.
Solution

759AEI-406.61 & 62
• It is desired to control flow B in a preset ratio to flow A.
• Flow transmitter senses the flow.
• Ratio relay multiplies the output of flow transmitter by a
manually set factor.
• o/p of ratio relay = (flow A output). (preset factor)

769AEI-406.61 & 62
Acid water ratio control system

779AEI-406.61 & 62
• The o/p becomes set point of controller that regulates
flow B
• At equilibrium, flow B equals the set point of controller
• Flow B = (flow A). (ratio factor)
• Ratio factor = flow B/ flow A

789AEI-406.61 & 62
APPLICATIONS OF RATIO CONTROL
(1. RATIO OF TWO REACTANTS)
• A most common ratio control is to control tae ratio of two
reactants entering a reactor at a desired value.
• In this case, one of the flow rates is measured but
allowed to float, that is, not regulated,& the other is both
control & controlled to provide the specified constant
ratio.

809AEI-406.61 & 62
(2.FUEL-AIR RATIO CONTROL)
• This ratio control is used to keep the ratio of fuel/air in a
burner at its optimum value.
• This is used to make sure the proper combustion of the
fuel with the just required amount of air.
• To control the temp. of a furnace, the fuel demand is
controlled by a cascade controller.
• This ratio controller may be used in series with temp.
control.

829AEI-406.61 & 62
(2.FUEL-AIR RATIO CONTROL)
• The fuel flow rate measured as secondary variable can
be used here as wild stream flow rate & given to ratio
setter.
• The o/p of the ratio setter is the set point for the ratio
controller which in turn changes the valve position of
the control valve in the air line to keep the desired
fuel/air ratio.

849AEI-406.61 & 62
(3.FUEL-AIR RATIO CONTROL FOR
BOILER)
• The fuel-air ratio control Is known as series control.
• This means the change in air flow rate occurs as per ratio
set only after the change has occurred in fuel flow rate.

859AEI-406.61 & 62
• But in boilers used in power plants, fuel & air should be
controlled in parallel rather then in series for safety
reasons.
• This is necessary because a lag of only one or two
seconds in measurement or transmission will seriously
upset combustion conditions in a series system.
• This can result in alternating periods of excess & deficient
combustion air.

879AEI-406.61 & 62
(3.FUEL-AIR RATIO CONTROL FOR
BOILER)
• One such parallel fuel-air ratio control used in boilers is
shown in fig.
• Firing rate demand from the master control of the boiler
is given as set point value to the fuel control.

889AEI-406.61 & 62
• Fuel flow rate changes as per the requirement of the
master control.
• The same firing rate demand signal is simultaneously
given to the air controller through a ratio setter so that
the air flow rate is controlled along with fuel flow rate
maintaining the proper ratio required for efficient
combustion.

899AEI-406.61 & 62
• Used to control of air flow in an oil fired furnace.
• Used to ensure proper mixer of solids (or) liquids in
reactant process.
Applications

909AEI-406.61 & 62
• Used in chemical processes where different process
parameters are inter related.
• Used in fuel blending.

Adaptive Control
9AEI-406.6391

9AEI-406.6392
FEEDBACK CONTROL
• The basic function of feedback in automatic control is to
maintain the process output at its set point, which may
be held constant or varied according to some desired
way, in the presence of unknown load disturbances or
minor uncertainty in the dynamic characteristics of the
process.

9AEI-406.6393
Necessity of Adaptive Control
• Feedback control works well if the controller parameters
have been properly designed or tuned according to the
process dynamic characteristics
• When the uncertainty in disturbance or process dynamic
characteristics is large, the performance of the fixed gain
feedback controller may become unacceptable and the
need for adaptive control arises

9AEI-406.6394
ADAPTIVE CONTROL
• Adaptive control may be viewed as an additional control
loop that adjusts the parameters of the feedback
controller to ensure that dynamic performance measures
such as damping and bandwidth are satisfied in the
presence of significant changes in process or
disturbance dynamics

9AEI-406.6395
DEFINITION
• Adaptive control may be defined as the mechanism for
implementing continuous automatic tuning of controller
parameters.

9AEI-406.6396
Adaptive Control
• An adaptive control system is one whose parameters are
automatically adjusted to meet corresponding variation in
the parameters of the process being controlled in order
to optimize the response of the control loop.

9AEI-406.6397
Block Diagram
Controller Process
Parameter
Adjustment
Rules
Set Point
Desired
Performance
Disturbance
Adaptive Control

9AEI-406.6398
TERMINOLOGY
• A adaptive control involves automatically detecting the
changes that occur in the gain or dead time of process
and readjusting the PID control mode settings, thereby
adapting the tuning of the loop to the changing
conditions.

9AEI-406.6399
TERMINOLOGY
• Adaptation can be based on the inputs (loads) entering
the process- this is called programmed (or feed-forward)
adaptation.
• A system that adapts on the basis of a measurement of
the disturbing factor is said to be programmed
adaptation.

9AEI-406.63100
TERMINOLOG
• When adaptation is based on the behavior of the
controlled variable (c) - this is called self adaptation (or
feedback adaptation).
• A system that adapts on the basis of a measurement of
its own performance is called self-adaptive.

9AEI-406.63101
TERMINOLOGY
• When the criteria for adaptation can be specified in the
steady state, it is called steady-state adaptive (or
optimizing) control.
• Eg:- The goal of setting the air-fuel ratio of a boiler so
that it will bring the process to maximum efficiency point
on its performance curve.

9AEI-406.63102
TERMINOLOGY
• When the criteria for modifying the tuning constants is
the damping of the controlled variable after an upset, the
method of adaptation is called dynamic adaptation
• Eg:- In pH control when the process gain (Kp) rises as the
process approaches neutrality, the increased process
gain results in the loop becoming unstable, then adaptive
controller serves to maintain correct damping when Kp
rises by lowering the controller gain (Kc).

103AEI- 406.64 & 65
TYPES OF ADAPTIVE CONTROL
• Adaptive control can be achieved by two ways
1. Programmed and scheduled adaptive controller.
2. Self adaptive control.

104AEI- 406.64 & 65
Programmed or Scheduled Adaptive
Control
• Where a measurable process variable produces a
predictable effect on the gain of the control loop,
compensation for its effect can be programmed into the
control system.
• Suppose that the process is well known and that an
adequate mathematical model for it is available.
• If there is an auxiliary process variable which correlates well
with the changes in process dynamics, we can relate ahead
of time the ‘best’ values of the controller parameters to the
value of the auxiliary process variable.

105AEI- 406.64 & 65
Block Diagram of Adaptive Control

107AEI- 406.64 & 65
• Consequently, by measuring the value of the auxiliary
variable we can ‘schedule or program’ the adaption of
the controller parameters.
• Fig. 2 shows the block diagram of a programmed
adaptive control system.

108AEI- 406.64 & 65
• We notice that it is composed of two loops. The inner
loop is an ordinary feedback control loop.
• The outer loop includes the parameter adjustment
(adaptation) mechanism and it is comparable to feed
forward compensation.

109AEI- 406.64 & 65
Gain scheduling adaptive controller
• In a normal feedback control loop shown in Fig. 3, the
control valve or another of its components may exhibit a
non linear character.
• In such a case the gain of the non linear component will
depend on the current steady state.
• Suppose that we want to keep the total gain of the
overall system constant.

111AEI- 406.64 & 65
Self-Adaptive Control
• If the process is not known well, we need to evaluate the
objective function on-line (while the process is operating)
using the values of the controlled output.
• The adaption mechanism will change the controller
parameters in such way as to optimize (maximize or
minimize) the value of the objective function (criterion).

112AEI- 406.64 & 65
Model-reference adaptive controller
(MRAC)
• Fig. 4 illustrates a different way to adjust the
parameters of the controller.
• We postulate a ‘reference model’ which tells us how the
controlled process output ideally should respond to the
command signal (set point).
• The model output is compared to the actual process
output.

114AEI- 406.64 & 65
• The difference (error – em) between the two outputs is
used through a computer to adjust the parameters of the
controller in such a way as to minimize the integral
square error:
• The model chosen by the control designer for reference
purposes is to a certain extend arbitary.

115AEI- 406.64 & 65
• Most often a rather simple linear model is used.
• We notice that the model-reference adaptive control is
composed of two loops.
• The inner loop is an ordinary feedback control loop.

116AEI- 406.64 & 65
• The router loop includes the adaptation mechanism and
also looks like a feedback loop.
• The model output plays the role of the set point while the
process output is the actual measurement.

117AEI- 406.64 & 65
• There is a comparator whose output is the input to the
adjustment mechanism.
• The key problem is to design the adaptation mechanism
in such a way as to provide a stable system (That is to
bring the error – em to zero).

118AEI- 406.64 & 65
Self-tuning regulator (STR)
• Consider the block diagram of Fig. 5
• It represents the structure of a self-tuning regulator, which
constitutes another way of adjusting the parameters of a
controller.
• The STR is composed, again, of two loops.

120AEI- 406.64 & 65
• The inner loop consists of the process and an ordinary
linear feedback controller.
• The outer loop is used to adjust the parameters of the
feedback controller and is composed of a recursive
parameter estimator and an adjustment mechanism for
the controller parameters.

121AEI- 406.64 & 65
INDUSTRIAL APPLICATIONS
Industry Loop Type (s)
Electronic pH-Cyanide Destruct
pH-Waste treatment

122AEI- 406.64 & 65
Industrial Applications (Contd)
Pulp & Paper
Chemical
Oil & Gas
Temperature, Pressure,
Flow Level, Steam Drum
Level, Crude Tower

123AEI- 406.64 & 65
Pulp & Paper pH-Waste Treatment
composition, White Liquor

124AEI- 406.64 & 65
Pulp & Paper
Chemical
Temperature super heater,
pH-Waste Treatment

Process control 4 chapter

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