1
Fundamentals TrainingThink About Control
Terminology Control
Control Fundamental - Con't
Eko Harsono
Contents
2
Topics: Slide No:• Advance Control Loop 3 - 10• Control Algorithm 11 - 25• Control System 26 - 32• Exercise 33 - 38
Control Fundamental - Con't
Advance Control Loop
3
Consist of one controller (primary, or master) controlling thevariable that is to be kept at a constant value, and a second controller(secondary, or slave) controlling another variable that can causefluctuations in the first variable. The primary controller positions theset point of the secondary, and it, in turn, manipulates the controlvalve.
What is CASCADE CONTROL ?What is CASCADE CONTROL ?
FBC FBC
Secondary Process
Primary Process
Secondary controller
Primary controller
Disturbancer1 r2 m
c1 c2
Multi-Variable Control
Control Fundamental - Con't
Advance Control Loop
4
The temperature of the liquid in the vessel is controlled by regulating the steam pressure in the jacket around the vessel.
Example of CASCADE CONTROLExample of CASCADE CONTROL
Temperature transmitter
Temperature controller
Measurement
Output
SteamValve
Jacket
IN
OUT
SINGLE-LOOP CONTROL
Pressure transmitter
Measurement Pressure controller
Cascade Control LoopControl Fundamental - Con't
Advance Control Loop
5
TemperatureProcess
Steam FlowProcess
Load A(Demand)
TIC
FT
TT
FC
Load B(Header Pressure)
SP RSP
__
I/P
TT
TIC
Steam
ColdWater
HotWater
Condensate
Major Load A:Outflow Rate(Demand)
Major Load B:Steam HeaderPressure
SteamHeader
FT
FC
RSP_
Implementing Cascade Control Implementing Cascade Control
Control Fundamental - Con't
Advance Control Loop
6
Applies to a system in which a balance between supply anddemand is achieved by measuring both demand potential anddemand load and using this data to govern supply. It gives asmoother and stable control than feedback control.
Level indicating controller
Flow controller
Boiler
FeedwaterFT
What is FEED FORWARD CONTROL ?What is FEED FORWARD CONTROL ?
FT LT
Steam
SP
PV O/P
Multi-Variable Control
Feed forwardSP
Control Fundamental - Con't
Advance Control Loop
7
I/P
TT
FeedforwardLoop
TIC
Steam
ColdWater
HotWater
FT
FFD
FeedforwardEquations
SummingJunction
FeedbackLoop
Implementing Feedforward ControlImplementing Feedforward Control
Control Fundamental - Con't
Advance Control Loop
8
An uncontrolled flow determines a second flow so that a desired ratio is maintained between them.
The ratio factor is set by a ratio relay or multiplying unit whichwould be located between the wild flow transmitter and the flowcontroller set point. Flow B is controlled in a preset ratio to flow A.
What is RATIO CONTROL ?What is RATIO CONTROL ?
Ratio relay
Wild flow, A
Controlled flow, B
Remote -set
controller
Output = A x ratio
SP
Output
Wild flow, A
Controlled flow, B
Ratio controller
Output
Multi-Variable Control
SP
Control Fundamental - Con't
Advance Control Loop
9
Example of RATIO CONTROLExample of RATIO CONTROL
Other Application : Fuel/air ratio control system on combustion equipment, e.g. boilers.
Acid supply
Magnetic flowmeter
Pickle tank
Flow transmitter
FT FC
Control valve
Flow BFlow AWater
Manual water regulator
MeasurementSet
Pickling Process
Control Fundamental - Con't
Advance Control Loop
10
The more important condition between two or more candidatesis selected. They are used mainly to provide protection to apiece of equipment which could suffer damage as a result ofabnormal operating conditions.
O/P
What is SELECTIVE CONTROL ?What is SELECTIVE CONTROL ?
Speed ControlPIC
PIC
RSLow select
PV
Pump
O/PO/P
PV
Multi-Variable Control
Control Fundamental - Con't
Control Algorithm
11
•• On/Off On/Off
•• MultiMulti--stepstep
•• ProportionalProportional
•• IntegralIntegral
•• DerivativeDerivative
Control Fundamental - Con't
Control Algorithm
12
It is a two-position control, merely a switch arranged to be off (or on as required) when the error is positive and on (or off as required) when the error is negative. Ex.. Oven & Alarm control.
OnOn--Off ControlOff Control
differentialMeasured variable
Controller output
Time
Control Fundamental - Con't
Control Algorithm
13
A controller action that may initiate more than two positioning of the control valve with respect to the respective predetermined input values.
MultiMulti--Step ActionStep Action
Multi-step actionTime
Time
1234
75
80
85
Control Fundamental - Con't
Control Algorithm
14
It is the basis for the 3-mode controller. The controller output (O/P) is proportional to the difference between Process Variable (PV) and the Set Point (SP).
Proportional Action (P)Proportional Action (P)
Process
Load
Controller
Output
SP
PV
Open-loop response of proportional modeControl Fundamental - Con't
Control Algorithm
15
When a disturbance alters the process away from the set-point, the controller acts to restore initial conditions. In equilibrium, offset (PV-SP = constant) results.
Proportional Action (P)Proportional Action (P)The Algorithm is :
O/P - (PV - SP)Proportional
Band
Constant= +
S - PV
O/P %100
(Constant is normally 50% )
50
Tan = Gain = 100 / Proportional Band
Time
SP
Time
Recovery time Offset
Many controllers have a ‘manual reset’. This enables the operators to manipulate the ‘constant’ term of the algorithm to eliminate offset.
PV
Control Fundamental - Con't
Control Algorithm
16
0 1 2 3 4 5 6 7 8 9Time
100
90
80
70
60
50
40
30
20
10
%
SP
PV
Output
E1E0 E2 E3 E4
prop
Low Proportional Gain: (Closed Loop)Low Proportional Gain: (Closed Loop)
Control Fundamental - Con't
Control Algorithm
17
0 1 2 3 4 5 6 7 8 9Time
100
90
80
70
60
50
40
30
20
10
%
SPPV
Output
higain
High Proportional Gain: (Closed Loop)High Proportional Gain: (Closed Loop)
Control Fundamental - Con't
Control Algorithm
18
Whilst PV SP, the controller operates to restore equality. As long as the measurement remains at the set point, there is no
change in the output due to the integral mode in the controller. The output of the controller changes at a rate proportional to
the offset. The integral time gives indication of the strength of this action. It is the time taken for integral action to counter the ‘offset’ induced by Proportional Action alone.
Integral Action (I)Integral Action (I)
Time
Set Point
% Measurement
% Output
Time
Set Point
a=b
RT
RT = Reset Time min./rpta {b {
Integral mode Proportional plus Integral mode
Open-loop response
Control Fundamental - Con't
Control Algorithm
19
0 1 2 3 4 5 6 7 8 9Time
100
90
80
70
60
50
40
30
20
10
%
SP
PV
ProportionalPlus IntegralOutput
ProportionalResponse
Integral Action: (Closed Loop)Integral Action: (Closed Loop)
Control Fundamental - Con't
Control Algorithm
20
As the PV changes, the controller resists the change. The controllers output is proportional to the rate at which the
difference between the measured and desired value changes. The derivative time is an indication of this action. It is the
time that the open-loop P+D response is ahead of the response due to P only.
Derivative Action (D)Derivative Action (D)
Time
Set Point
% Measurement
% Output (I/D)
Derivative mode
Time
Set Point
DT
DT = Derivative Time (min)
Proportional plus Derivative mode
Open-loop response
Proportional + Derivative
Proportional only
Control Fundamental - Con't
Control Algorithm
21
0 1 2 3 4 5 6 7 8 9Time
100
90
80
70
60
50
40
30
20
10
%
SP
PV PID Output
PID Action: (Closed Loop)PID Action: (Closed Loop)
Control Fundamental - Con't
Control Algorithm
22
PID ControlPID Control
A
B
80
60
40
20% S
cale
Ran
geC
ontro
ller O
utpu
tor
Valv
e P
ositi
onMeasurement
Proportional
Time - minutes
Open-loop response of three-mode controller
Proportional + Integral + Derivative
Proportional + Integral
Control Fundamental - Con't
Control Algorithm
23
I/P
PT
PIC
P
P & ID Piping & Instrumentation DrawingP & ID Piping & Instrumentation Drawing
Process Vessel
Fluid Pump
PneumaticControlValve
Compressed Air Pipe
ConverterPID
Controller
PressureTransmitter
Control Fundamental - Con't
Control Algorithm
24
Controller SelectionController Selection
Can offset be tolerated ?
Start
UseP-only
Yes
UseP+I
Yes
No
Is dead time excessive ?
No
UsePID
Yes
Is noise present ?
No Reaction curve of measured
variable
CapacityDead Time
C
63.2%
Time (sec)
Step change in valve travel
Control Fundamental - Con't
Control Algorithm
25
Controller AdjustmentController Adjustment
Time
Con
trolle
d Va
riabl
e Period
P-only
PID
PI
Control loop Proportional band Time constant DerivativeFlow High (250%) Fast (1 to 15 sec) NeverLevel Low Capacity dependent RarelyTemperature Low Capacity dependent UsuallyAnalytical High Usually slow SometimesPressure Low Usually fast SometimesControl Fundamental - Con't
Control System
26
An automatic control scheme in which the controller is programmed to evaluate its own effectiveness and modify its own control parameters to respond to dynamic conditions occurring in or to the process which affect the controlled variables.
Adaptive ControlAdaptive Control
Ex) Digital Controller- Sensors are run to the computer’s input. - Servomechanisms are connected to the computer’s output.- Future changes don’t require re-wiring.- Changing control functions (P,I, and D) and configurations (between cascade mode and feedforward mode) will be made on the computer’s program and not necessarily to any hardware.
Control Fundamental - Con't
Control System
27
A control strategy where the process control computer performs system control calculations and provides its output to the setpoints inputs of conventional analog controllers. These analog controllers actually control the process actuators, not the main-control computer.
Supervisory ControlSupervisory Control
M.I.S Supervisory Control
A
S
Controller
S
AController
S
AController
SP1
SP2
SP3
Control Fundamental - Con't
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Control System
Measurement
HW andSoftwareFiltering
I/O Rack
Coax
ControllerTools for Process Analysis, Diagnostics.
SampledValue
Tools for Process Analysis, Diagnostics.
ControllerI/O Rack
Today’s DCS SystemToday’s DCS System
Control Fundamental - Con't
Control System
29
Definition...
Control roomoperator stations
Control systems(DCS or PLC)
A digital, two-way, multi-drop communication link among intelligent field devices and automation systems.
Fieldbus (Only Digital Signals)
What is a FIELDBUS ?What is a FIELDBUS ?
P
T
L
F
Control Fundamental - Con't
Control System
30
Gateway HSE
H1H1H1H1
BridgeH2
H1
H1
124Devices
Work Systems
H1 - 31.25 Kbit/sHSE - 100 M bit/s(Fast Ethernet)
(due to address limits) .Total of approximately 35,000 devices
Fieldbus Control SystemFieldbus Control System
Controller
32 Devices
32DevicesControl Fundamental - Con't
Control System
31
AI
PID
AI AO
PID
DCS
4 -20 mA 4 -20 mA4 -20 mA
ADVANCED CONTROL OPTIMIZATION
•• Control in the control roomControl in the control room
Proprietary BusProprietary Bus
Control Fundamental - Con't
Control System
32
PIDIN OUT
BKCAL_IN FIELDVUE
AO
BKCAL_OUT
CAS_IN
AIOUT
Delta V
Valve
Transmitter
Control Control AnywhereAnywhere
BuiltBuilt--InInFunction Function BlocksBlocks
Foundation Fieldbus DevicesFoundation Fieldbus Devices
•• Control in the field with fieldbusControl in the field with fieldbusControl Fundamental - Con't
Look at how the CONTROL migrate
33
FCS
Loop 1 Loop 2
Digital
PID PID
DCS
Loop 1 Loop 2
Digital
PID
Analog
DDC
Analog
PID
Loop 1 Loop 2
Central Control Loop
Local Control Loop
Control in the field
Control in the device itself
Control Fundamental - Con't
Exercise
34
Which defined term is closest to the description or encompasses the example given?
A.Controller F. Primary element
B. Converter G. Signal
C. Instrument H. Transducer
D.Point of measurement I. Transmitter
E. Process
1. Process temperature increases the measurable resistance in a monitored electrical circuit. [ ]
2. Pulsed output from a turbine meter. [ ] 3. Heat-injected plastic molding. [ ]
Control Fundamental - Con't
Exercise
35
4. Temperature transmitter. [ ]
5. Device which adjusts the measured value of the process to the requirements of the operator. [ ]
6. Element, flow transmitter, controller and correcting unit. [ ]
7. A pipe piece is tapped for a sample fluid. [ ]
8. A device changes an industry standard pneumatic signal to an industry standard hydraulic signal. [ ]
Control Fundamental - Con't
Exercise
36
9. Identify the components indicated by the Arrows.
Control Fundamental - Con't
Exercise
37
Which defined term is closest to the description or encompasses the example given.
A. Cascade control F. GainB. Control algorithm G. OffsetC. Control valve H. Proprietary BusD. Feed-forward control I. Smart Device E. Foundation Fieldbus
10. The predefined response of the controller to PV-SP. [ ]
11. The value of PV-SP when the system is in equilibrium. [ ]
12. The ratio of controller’s output to input. [ ]
13. It is a final control element operated by an actuator. [ ]
Control Fundamental - Con't
Exercise
38
14. Involves master & slave controllers. [ ]
15. The output of the loop drives the input. [ ]
16. A digital communication based control network with control action in the controller only. [ ]
17. A digital communication based control network that allow control in the field. [ ]
18. A device that provide both analog & communication signal in its loop wire pair. [ ]
Control Fundamental - Con't
Reference A Smith-Corripio [1997]. Principles and Practice
of Automatic Process Control 2nd Edition, John Willey & Sons
Ogata [2010]. Modern Control Engineering 5th
Edition, Prentice Hall Rosemont [2002]. Fundamental Control Training http://www.isa.org
39 Control Fundamental - Con't