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Appied Process Control Systems
Fundamentals of Process
Control SystemsLe c t u r e - 1
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. .
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Sequence of Presentation
1.Why Process Control?
.
3.Role of Sensors and Instruments
4.Modes Of Control Systems
6.Examples of Servo Control Systems
7.Conclusions
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1. Why Process Control ?
1.Safety of Equipment and Personnel
.
quantity
.
4.Observe Environmental and Countryaws
5.Economics
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Control Objectives
1. Safety ofEquipment &
Give example
personnel
2. ProductionSpecification of
Vapo
ProductT6 PC
quality &quantity
3. Operational F1
T2
T4 T3 L1
Feed
Constraints
4. EnvironmentalRegulations
F3F2
5. Economics productSteamProcessfluid L. Key
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Safety of Equipment & Personnel
1. Safety ofEquipment &
High pressurein drum isdangerous
Va o
2. ProductionSpecification of
Product
T1 T5Feed
quantity
3. OperationalConstraints
F1 T4T3 L1
4. EnvironmentalRegulations
Liquid
F3F2
A1
. conomcs productSteamrocessfluid L. Key
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Control Objectives
1. Safety ofEquipment &
Give example
personnel
2. ProductionSpecification of
Vapo
ProductT6 PC
quality &quantity
3. Operational F1
T2
T4 T3 L1
Feed
Constraints
4. EnvironmentalRegulations
F3F2
5. Economics productSteamProcessfluid L. Key
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Safety of Equipment
1. Safety ofEquipment & VaporT6 PC
No flow coulddamage thepump
personne
2. ProductionSpecification of
Product
T1 T2 T5qua yquantity
3. Operational
F1 T4 T3L1
ee
4. EnvironmentalRegulations Liquid
F3F2
A1
5. Economics pro ucfluid L. Key
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Quality Assurance
1. Safety ofEquipment &
Give Example
personnel
2. ProductionSpecification of
Product
quality &quantity
3. Operational F1 T4 T3 L1
Feed
Constraints
4. EnvironmentalRegulations
F3F2
5. Economics productSteamProcessfluid L. Key
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Quality Assurance
1. Safety of
Achieve L.Keyby adjusting
personnel2. Production
VaporProductT6 PC
quality &quantity
T1
F1
T2
T4
T5
T3
Feed
.Constraints
4. Environmental F3F2
5. EconomicsLiquidproductSteamProcess
fluid L. Key
A1
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Observe Environmental and Other Regulations
1. Safety ofNever releaseh drocarbons
qupmen
personnel
2. Production
VaporProduct
T6 PCto atmosphere
pec ca on oquality &
quantity
T1
F1
T2
T4 T3 L1
Feed
.Constraints
4. Environmental F3F2
5. Economicsqu
productSteamProcessfluid L. Key
A1
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Economics
1. Safety ofGive Example
qupmen
personnel
2. Production
VaporProductT6 PC
pec ca on oquality &
quantity
T1
F1
T2
T4
T5Feed
.Constraints
4. Environmental F3F2
5. EconomicsLiquidproductSteamProcess
fluid L. Key
A1
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Economics
1. Safety ofEquipment &personnel
2. ProductionSpecification of
Give Example
quality &quantity
3. Operationalonstrants
4. EnvironmentalRegulations
5. Economics
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2. What to Control ?
1.The Influence of External
2.Ensure Stable Operation
(Avoid Unsteady State)
. p m ze pera on
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Suppress the Influence of External Disturbances
Disturbances?
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Ensure Stable Operation
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Optimized Operation (online)
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Potential Stochastic Gains through effective Process Control
When we control a process, we reduce the variabil ity.
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Potential Stochastic Gains through effective Process Control (Contd)
Variability is moved from controlled to manipulated variable!
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Potential Stochastic Gains through effective Process Control (Contd)
What statisticscan we cacua e
from this data?
How do we relatevariability to process
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Potential Stochastic Gains through effective Process Control (Contd)
Process erformance
efficiency, yield,production rate, etc. It
for a control objective.
Calculate the process
performance using the
,average value of the key
variable!
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Comment on Sensors and Instruments
operator that can see & feel the intenseprocess variable inside the vessels
` Accordingly the measurements should be
possible with reasonable costs.
` Process control go hand in hand
If you cannot measure you cannot control!
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4. Modes of Control Systems
` Feedback Control Systems (Regulatory)
` Feedforward Control Systems(Servo, Tracking)
` Sequential Control System
` Distributed
Modes of Implementation
` Pneumatic
` Electronic
` Digital
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Basics of feedback control system
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Examples of feedback system
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Examples of feedback system
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Examples of feedback system
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Examples of feedback system
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Example of Temperature Control (Heat exchanger)
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Example of Composition Control
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Where is Control Done?
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Control Systems Implementations In Industry
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Control Systems Implementations In Industry
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Control Systems Implementations In Industry
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Applied Process Control System
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 1
pp y
Sensors &
Instrumentation
Dr. Ing. Naveed Ramzan
Le c t u r e - 2
Sequence of Lecture
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Instruments are our eyes
Performance characteristics of Instruments
Principle measurements desired in industry
(a) Temperature
(b) Pressure(c) Level(d) Flow(e) Others ( Composition, pH etc.)
q
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Importance of effectivemeasurement in process
industry
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Failure to measure effectively the level of liquidin bottom of the tower lead to
--- Fire
--- Explosion
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Functional Elements of an Instrument
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Process/Measured medium
Primary
Sensing
Element
Variable
Conversion
Element
Variable
Manipulation
Element
Data
Transmission
Element
Data
Presentation
Element
Observer
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Functional Elements of an Instrument (Contd)
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Typical Example:
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Functional Elements of an Instrument (Contd)
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Primary
SensingElement
Variable
ConversionElement
Data
TransmissionElement
Variable
Manipulation
Element
Data
Presentation
Element
TemperatureMeasured
Quantity
Pressure
Variable
Conversion
Element
Pressure
MotionMotion
Fluid
Temperature Tube Tubing
Spiral Bourdon
Tube
Linkage GearScale & Pointer
Observer
Process/Measured medium
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Performance Characteristics of Instruments (Contd)
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Static characteristics
Static characteristics of an instrument includes;
Accuracy
Precision
Repeatability
Range
Resolution
Others ( Sensitivity , Dead zone etc.)
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Static Characteristics
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Static characteristics of an instrument includes;
1. Accuracy
The ability of a device or asystem to respond to a truevalue of a measured variable
under reference conditions.
In general accuracy
expressed as Limit of Error
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Static Characteristics
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Static characteristics of an instrument includes;
3. Repeatability
Repeatability is the variation in measurements takenby a single person or instruments on the same itemand under the same conditions.
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Calibration
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Assigning standardvalues to anequipment iscalibration.
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Performance Characteristics
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Dynamic characteristics
Dynamic Characteristics of an instrument includes;
1. Speed of response
2. Fidelity
3. Lag
4. Drift
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Principle measurements desired in Industry
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Principle measurements desired in industry
(a) Temperature
(b) Pressure
(c) Level
(d) Flow
(e) Others ( Composition, pH etc.)
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It is time to turn up the heat but
first you must learn how tomeasure it
Temperature Sensor
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Methods of Temperature Measurement
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1. Thermocouples
2. Thermistors
3. Electrical resistance change (RTD)4. Expansion of materials
5. Pyrometers
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Thermocouple Types
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TCs are identified by a single letter type andgrouped according to their temperaturerange
` Base Metals up to 1000 C
` Type J, Type E, Type T, Type K
` Noble Metals up to 2000 C
` Type R, Type S, Type B
` Refractory Metals up to 2600 C
` Type C, Type D, Type G
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Metal Combinations
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TC
Type
Colours Range C Positive Lead
(Coloured)
Negative Lead
(all Red)J White/Red -210 to 1200 Iron Constantan
E Purple/Red -270 to1000 Chromel Constantan
T Blue/Red 0 to 400 Copper Constantan
K Yellow/Red -270 to1372 Chromel Alumel
R Black/Red -50 to 1768 Platinum-13%rhodium
Platinum
S Black/Red -50 to 1768 Platinum-10%rhodium Platinum
B Grey/Red 0 to 1700 Platinum-30%rhodium
Platinum-6% rhodium
C White-Red/Red 0 to 2320 Tungsten/5%rhenium Tungsten 26% rhenium
Chromel = Nickel-chromiumAlumel = Nickel-aluminum
Constantan = Copper-nickel
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Thermocouple Tables
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Type T Thermocouple (Blue & Red) Reference Junction 0 C
C 0 1 2 3 4 5 6 7 8 9
0 0.000 0.039 0.078 0.117 0.156 0.195 0.234 0.273 0.312 0.352
10 0.391 0.431 0.470 0.510 0.549 0.589 0.629 0.669 0.709 0.749
20 0.790 0.830 0.870 0.911 0.951 0.992 1.033 1.074 1.114 1.155
30 1.196 1.238 1.279 1.320 1.362 1.403 1.445 1.486 1.528 1.570
40 1.612 1.654 1.696 1.738 1.780 1.823 1.865 1.908 1.950 1.993
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Thermistors
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` The thermistors can be in the shape of a rod,
bead or disc.
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` Manufactured from oxides of nickel, manganese,
iron, cobalt, magnesium, titanium and othermetals.
Thermistors
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Advantages:
` Small sizes and fast response
` Low cost
` Suitability for narrow spans
Disadvantages:
`More susceptible to permanent decalibration athigh temperatures.
` Use is limited to a few hundred degrees Celsius.
` Respond quickly to temperature changes, thus,especially susceptible to self-heating errors.
` Very fragile
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Electrical Resistance Change (RTD)
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Resistance Temperature Detector- RTD
` RTD (Resistance Temperature Detector) is a
temperature sensitive resistor.
` It is a positive temperature coefficient device, which
means that the resistance increases with temperature.` The resistive property of the metal is called its
resistivity.
The industry standard is the platinum wire RTD(Pt100) whose base resistance is exactly 100.00
ohms at 0.0 C.
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Electrical Resistance Change (RTD)
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Platinum Wire RTDs (PRTs)
PRTs have established themselves as the de-facto industrystandard for temperature measurement, and for many reasons:
` linear temperature sensors
` Resistance vs temperaturecharacteristics are stable andreproducible
` linear positive temperature
coefficient (-200 to 800 C)
` very accurate and suitable for use asa secondary standard
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Electrical Resistance Change (RTD)
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OtherRTDs` 10 ohms Copper RTD - .00427 coefficients
` 100 ohms Platinum RTD - .00385 coefficients
(new IEC)
` 100 ohms Platinum RTD - .00392 coefficients (old)
` 120 ohms Nickel RTD - .00672 coefficient
` 604 ohms Nickel-Iron RTD - .00518 coefficients
All base resistances are specified at a temperature of 0 degrees C
A Pt1000 will have a base resistance of 1000 ohms at 0 deg. C
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RTD Colour Code
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Not standardized but this is commoncolour arrangement. Some (like in thelab) will use BLK-BLK-RED
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Expansion Thermometers
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` Bimetallic Thermometer
(Expansion of solids)
Effect of unequal expansion of a bimetallic strip
Bimetallic thermometer
-Different metals have difference coefficient.
-Configured as spiral or helix for compactness
- Can be used with a pointer to make aninexpensive compact rugged thermometer.
Expansion Thermometers
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` Filled Thermal Systems
(Filled System Thermometer, Filled Bulb Thermometer)
Similar operation as the liquid in glass
`Bulb
` Capillary tube
` Pressure element
` Scale
Spiral TypeBourdon Tube
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Expansion Thermometers
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` Filled Thermal System Classes(Filled System Thermometer, Filled Bulb Thermometer)
` Class l A,B Liquid filled
` Class ll A,B,C,D Vapour filled
` Class lll A,B Gas filled
` Class V A,B Mercury Filled
Temperature Range Response
` Class l: -125 F to + 600 F Slowest
` Class ll:
-40 to 32 or 32 to 600 F Fastest
` Class lll: -450 F to +1400 F Fast
` Class V: -40 F to +1200 F Fast
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Pyrometer
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Pyrometry is a technique for measuring temperature without
physical contactAn apparatus for measuring high temperatures that uses
the radiation emitted by a hot body as a basis formeasurement.
` Radiation pyrometers ( measurement of radiant energy)
` Optical Pyrometers (comparison of the intensities )
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Pressure Sensors
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In any given plant, the number of
pressure gauges used is probablylarger than all other instruments
put together
Pressure Measurement Methods
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1. Elastic pressure transducers
2. Electric pressure transducers
3. Pressure measurement by measuring vacuum
4. Pressure measurement by balancing forcesproduced on a known area by a measured force
5. Manometer method
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Elastic Pressure Transducers
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1. Bourdon tube pressure gauge
2. Diaphragm pressure transducers
3. Bellows
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Bourdon Tube Pressure Gauge
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40
Bourdon tubes are generallyare of three types;
1. C-type
2. Helical type3. Spiral type
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Diaphragm Pressure Gauge
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They are used to measure gauge pressures over very low
ranges.` Two types of diaphragm pressure guages are:
1. Metallic diaphragms gauge2. Slack diaphragms gauge
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Bellows
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` More sensitivethan bourdontype gauge.
` Used to measurelow pressures
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Electric Pressure Transducers
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Electrical pressure transducers consists of three
elements
1. Pressure sensing element such as a bellow , adiaphragm or a bourdon tube
2. Primary conversion element e.g. resistance orvoltage
3. Secondary conversion
element
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Strain Gauge Pressure Transducer
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A strain gauge is a passive type resistance pressure transducer
whose electrical resistance changes when it is stretched orcompressed
A pressure transducer contains a diaphragm which is deformedby the pressure which can cause a strain gauge to stretch orcompress. This deformation of the strain gauge causes thevariation in length and cross sectional area due to which its
resistance changes.
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Capacitive Pressure Transducer
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The sensing diaphragm and capacitor form a differentialvariable separation capacitor. When the two inputpressures are equal the diaphragm is positioned centrallyand the capacitance are equal. A difference in the two input
pressure causes displacement of the sensing diaphragmand is sensed as a difference between the two capacitances
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Differential Pressure Cell (DP Cell)
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It is a device that measures the differential pressure
between two inputs.
Depending on what class theDP-cell is, it will give youfeedback with a current signal.
Normal in Europe is 4-20mA, where 4 is lowest and 20is highest.
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Using a d/P Cell Transmitter
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In a closed tank, the Low side of the d/P cell is
connected to the top of the tank and will cancelthe effects of the vapour pressure above thesurface.
Closed Tank Measurement Lo side of the d/P cell measures the vapour pressure above the surface. Hi side measures the hydrostatic head pressure which is proportional to
the height of the liquid and its density + vapour pressure
24 VDC mA
4 20 mA
To PLC orController
H L
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Level Sensors
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Level is another common process variable that is
Level Measurement
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Level is another common process variable that ismeasured in many industries. The method used will
vary widely depending on the nature of the industry,the process, and the application.
Inventory:
-- a constant supply or storage of materialControl:-- continuous, batch, blending, and mixing control
-- stabilize flow to the next processAlarming:-- hi/lo limits, safety shut downData Logging:-- material quantities for inventory and billing
purposes and where regulatory requirements arenecessary
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Methods ---- Direct or Indirect (inferential)
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` Hydrostatic Head` Float` Load Cells` Magnetic Level
Gauge` Capacitance
Transmitters` Magnetostrictive
` Ultrasonic` Microwave` Laser` Radar
` Guided WaveRadar
` Dip Stick` Vibration
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Selection Criteria
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When determining the type of level sensor thatshould be used for a given application, there area series of questions that must be answered:
` Open tank or closed tank?` Can the level sensor be inserted into the tank or
should it be completely external? Contact or non-
contact?` Continuous measurement or point measurement?
` Direct or Indirect measurement?
` What type of material is being measured? Liquidor Solid? Clean or Slurry?
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Dip Stick
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` Simple and cheap
` Can be used with any wet
material and not affectedby density.
` Can not be used with
pressurized tanks` Visual indication only
(electronic versions are
available)
RodGauge - similar to a dipstick found in a car, it has weighted
line markings to indicate depth or volumePEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 53
Th f th fl id i th t k th
Resistance Tape
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The pressure of the fluid in the tank causes the
tape to short-circuit, thus changing the totalresistance of the measuring tape. An electroniccircuit measures the resistance; it's directlyrelated to the liquid level in the tank.
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Magnetic Level Sensor
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Used where the sightglass level gauge cannot be used.
Magneto-resistive typescan provide an
electrical output.
Liquid/liquid interface (such as water and oil) can be measured bychanging the buoyancy of the magnetic float
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Floats
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Float rides the surface level to provide the
measurement. Many different styles areavailable.
Liquid density does not affect measurementPEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 57
Hydrostatic Head Level Sensors
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` These methods infer level by measuring
the hydrostatic head produced by theliquid column.
`A pressure sensing element is installedat the bottom of the tank and pressure
is converted to level.
`Different liquid densities or closed tankapplications must be accounted for.
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Practical Considerations when usingHydrostatic Head Level Sensors (Contd)
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g
head type instrumentsThe reference point of the tank vs
instrument input must be considered.
Height
(H)
Pressure PSI
Liquid Density
(D)Height
(H)Pressure
PSI
Liquid Density
(D)
This may not be practical in some applications where the tank elevationis below grade or where a remote visual reading is required.
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Bubblers
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Bubblers allow theindicator to belocated
anywhere.
The air pressure in
the tube varieswith the headpressure of the
height of theliquid.
Bottom of tubedetermines reference
point
P
Regulated purgesystem
(air or nitrogen)
Instrument inputdoes not matter
Cant be used in closed tanks or where purging a liquid is not allowed (soap). Very
popular in the paper industry because the air purge keeps the tube from plugging.
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Conductivity Level Measurement
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Po i n t Le v e l M e a su r em e n t Co n t i n u o u s Le v e l M e a su r em e n t
Advantages and disadvantages
Low Cost
Conductive, non-coating liquids onlyInsulating coatings can cause problems
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UltraSonic Level Measurement
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` Non-Contact direct levelsensor
` Level is a function of thetime it takes an ultrasonicpulse to hit the surface andreturn
Limitations include:
Surface foam absorbs signal, agitation create reflections
High Pressure & High Temperatures affect the signal speed
Vapour and condensate create false echos
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Load Cells
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Tank level is determined by theweight of the quantity of
materialLoad Cells (strain gauge
transducers) placed at thebottom of the tank measurethe weight and then convert itto an electrical signal.
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Flow Sensors
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` Pl t t l f d t lit d f t
Reasons for Flow Metering
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` Plant control, for product quality and safety
reasons.` Custody transfer, both interplant and selling to
outside customers.
` Filling of containers, stock tanks andtransporters.
` Energy, mass balancing for costing purpose
and health monitoring of heat exchangers.` Health monitoring of pipelines and on-line
analysis equipment, Government and
company legislation may dictate the use hereof such equipment.
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` Differential Pressure Meters
Types of Flow Meters
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` Differential Pressure Meters.
` Rotary Meters.1. Displacement2. Inferential
` New Flow Meters.1. Electromagnetic2. Vortex Shedding3. Ultrasonic4. Cross Correlation
5. Tracer6. Swirl7. Fluidic
` Point Velocity Meters.` Mass Flow Maters.
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` Orifice Plate
Differential Pressure Meters
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` Orifice Plate
` Dall Tube` Venturi Tube
` Pitot Tube
` Rota meter
` Target mater
` Averaging Pitot
` Nozzle
` Spring Loaded
` Intake Meter` Elbow Meter
` Bypass Meter
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Differential Pressure Meters ( Contd)
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Elbow Flow meter Rota meter
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Di l t M t
Rotary Meters ( Displacement Meters)
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Displacement Meters
` Gear
` Oval wheel
` Vane Meter
` Gear (Roots)
` Diaphragm Meter
`Liquid Sealed Meter
Inferential Meters
` Turbine Meter
` Hoverflo Meter
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Turbine Flow Meters
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 72
` Electromagnetic
New Flow Meters
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` Electromagnetic
EM Meter
` Vortex Shedding Meter
Vortex Generation Meter
` Ultrasonic Flow Meters
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New Flow Meters (Contd)
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Magnetic Flowmeter
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New Flow Meters (Contd)
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Swirl Meter
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Coriolis Mass Flowmeter
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Discussion & Questions?
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 1
Design of Control Systems& Standard Practices
Prof. Dr. Shahid Naveed
Le c t u r e - 3
Sequence of Presentation
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1.Design Objectives and Variables2.Steps in Design of a Control System
3.Standard Practices
4.Controller Selection & Tuning
5.Conclusion
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Variables in a Chemical Process
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 3
Hardware for a process Control System
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Steps in Design of a Control System
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1.Define the control objective(Purpose)
2.Select the measurement variable/s
(Primary / Secondary measurements, Easily, Rapidly, Reliably)
3. Select the manipulated variable/s (Utility/process)
4. Choose the control configuration (ConfigurationStandard/New)
5. Design/choose the controller
(Degree of controllability desired)
6.Design of multiple input multiple outputsystems (MIMO)
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General Control Configuration
F d b k t l
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Fe e d - f o r w a r d co n t r o l
Fe e d b a ck co n t r o l
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Recommended ControlSchemes and Standard
Practices
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Level Control
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Flow Control
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Pump Control
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Steam Turbine Driven Pump Control
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Rotary Pump Control
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Temperature Control of HE
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Temperature Control of HE (contd)
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Temperature Control of HE (contd)
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Pressure Control of Pressure Vessel
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Pressure Control of Pressurized Vessels
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Cascade Control
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Split Range Control
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Ratio Control
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Pressure Control (Contd)
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Controller Selection &Tuning Methods
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Available Methods
Controller Selection & Controller Tuning
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Available Methods
Ziegler-Nichols Tuning Technique
Cohen-Coon Setting
Quartering Technique
Minimum Offset
Minimum Integral Square Error ISE Minimum Integral Time Average Error ITAE
Minimum Integral Average Error IAE
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 27
Ziegler-Nichols tuning technique
It is for closed response system.
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Kc Ti (min) Td (min)
Proportional - -
Proportional -integral
Proportional
integral derivative
2Ku
2.2Ku
7.1Ku
2.1Pu
2Pu
8Pu
M1
oWc
2cycle
min
Where;Ultimate gain = Ku =
Ultimate period =Pu =
(M is the amplitude ratio for sustained oscillations )
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 28
Cohen Coons Method
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Input
Outpu
A
BK == (at steady state)
S
BT = B=ultimate response, td=time elapsed until system started to response
S=slope of curve
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Other Methods of Tuning Controllers
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QuarteringMinimum Offset
Minimum Integral-Square Error
( )=
dttISE2
( )=
dtttITAE
( )dttIAE =
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The general guidelines for tuning are as follows:
Selecting the Best controller and the values of P, I, D
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` If you want to strongly suppress the Large Errors , ISEis better than IEA because the errors are squared andthat contribute more to the value of the integral.
` If you want to suppress the Small Errors, IAE is betterthan ISE because when square small numbers (smallerthan one) they become even smaller.
` To suppress errors that persist for Long Times, the ITAEcriteria will tune the controllers better because thepresence of large t amplifies the effect of even smallerrors in the value integral.
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 31
Selecting the Best controller and the values of P, I, D
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 32
General Criteria to Select Feed Back Controller
` Define approximate performance criteria
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` Define approximate performance criteriaISE, IAE or ITAE.
`
Compute the value of the performancecriteria using P or PI or PID controller withthe best adjusted Kc, Ti, and Td.
` Select the Controller that gives the BESTvalue for the performance criteria.
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 33
Rules of Thumb
` If possible use simple proportional (P)
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controllers.
` If simple Proportional action is
unacceptable use a Proportional Integral(PI) controller.
`Use a Proportional Integral Derivative(PID) control to increase the speed ofresponse and retain robustness.
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 34
Critical Features of P, PI & PID Controllers.
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 35
Summary & Conclusion
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Design of Control System is a science andan art.
Recommended control practices play an
important role in it.
The role of engineer stretches far beyond
its design in application throughunderstanding
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 36
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Applied Process Control System
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 1
Computer ControlSystems
Dr. Ing. Naveed Ramzan
Le c t u r e - 4
Sequence of Presentation
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 2
` Basics of Computerized Control
` Essential components of computer control system
` Advantages of Computer Control
`Types of computer control implementation
Evolution of Process Control
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 3
Feedback Control Loop
Single Loop Control (SLC)
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 4
Traditional Single Loop Controller
Single Loop Control (SLC) (Contd)
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 5
From Traditional Analog Controller to Computer Control
Single Loop Control (SLC) (Contd)
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 6
Multiple loop Control
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 7
Actuators Process
Essential Components of Computer Control
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Hold Amplifier
DA Converter
Multiplexer
Digital
Computer
OperatorLog
Sensors
Instrumentation
Multiplexer
Amplifier/
Attenuator
A D Converter
Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 8
Essential Components of Computer Control (Contd)
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 9
Essential Components of Computer Control (Contd)
Types of Signal
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 10
MemorySlowFast
Essential Components of Computer Control (Contd)
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Input-OutputInterface
Digital Analog
I/0 I/0
Mass Storage
DisksFixed HeadMoving HeadFloppy
Magnetic Tapes
CommunicationPeripherals
PrintersType writersVideo Display unitGraphic TerminalsCard Reader
X-Y Platters
CentralProcessing Unit (CPU)
Basic FeaturesControllersArithmetic UnitLogical UnitRegisters
OptionsFloating Point ProcessorReal time ClockPower fail-safe auto restartWatchdog timer
ROM
Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 11
Components of digitalcomputer
Plant Inputs : Multiplexing
Essential Components of Computer Control (Contd)
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 12
` Control System
Process control computer vs data processing computer
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 13
Figure 1b
` Monitoring System
Process control computer vs data processing computer
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 14
Figure 1a
Advantages of Computer Control
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 15
-- all plant data is available at a central point and/or distributedpoints around the plant or works
-- alarm conditions are detected and reported quickly
-- plant is run according to the plan set by management, whichmay not be the case where there is a lot of manual
intervention
-- displays and printouts of information are available readily
-- changes to the operating conditions or recipes are made insmooth, repeatable and closely controlled manner
-- written records of all alarms and operator actions are
Advantages of Computer Control
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 16
available for post-incident or routine analysis
-- alarm conditions are detected and reported quickly
-- control room and control panel size is reduced
-- all batches of material are treated identically
-- batch logs are recorded automatically
-- complex start-up and shut-down procedure can be automated
-- safety interlocks can be programmed into the system
Direct Digital Control loop
Types of Computer Control Implementation
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 17
Figure 4
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Direct Digital Control loop
Types of Computer Control Implementation
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 19
Digitally Directed Analog Control (DDAC)
- Supervisory computer control
Types of Computer Control Implementation
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 20
Figure 4
Digitally Directed Analog Control (DDAC)
- Supervisory computer control
Types of Computer Control Implementation
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 21
Figure 4
Simplified Diagram of supervisory control
Types of Computer Control Implementation
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Supervisory computer control
Types of Computer Control Implementation
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 24
Distributed Control System
Types of Computer Control Implementation
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Distributed Control System
Types of Computer Control Implementation
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Programmable Logic Controller
Types of Computer Control Implementation
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Types of Computer Control Implementation
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Programmable Logic Controller
Types of Computer Control Implementation
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Programmable Logic Controller
Types of Computer Control Implementation
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Programmable Logic Controller
Types of Computer Control Implementation
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Programmable Logic Controller
Types of Computer Control Implementation
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Programmable Logic Controller
Types of Computer Control Implementation
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Comparing DCS with PLC for ease of configuration
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Emerging (Ideal) Configuration
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 36
Integrated Computer Control System
Types of Computer Control Implementation
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 37
Integrated Computer Control System for a paper and pulp mill
Types of Computer Control Implementation
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Traditional SCADA
Types of Computer Control Implementation
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 39
Field Instrumentation
Remote Stations
Communications Network
Central Monitoring Station
Water distribution system using SCADA
Types of Computer Control Implementation
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Dr. Shahid Naveed 9. April 2009/ Dr. Ing Naveed Ramzan 40
Discussion
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Discussion
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PEC Islamabad UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 1
Fundamentals of
Distributed ControlSystems
Prof. Dr. Shahid Naveed
L ec t u r e - 5
Mainframe To Distributed Control
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DCS is a Computer Network with Control Objectives
1. The usual benefits of computer network on
Ethernet (or like) are availed e.g. resourcesharing (hard/soft) backup/archive database
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Ethernet (or like) are availed e.g. resourcesharing (hard/soft), backup/archive, databaseupdating, control algorithm computation, datalogging etc
2. Each Local Control Unit (LCU) is used tocontrol the process variables. The informationin shared through communication interfaces
for multiple usage and Low/High LevelInterfaces.
3. The High Level Human Interface (HLHI) is
provided in the control room and formanagerial applications throughout the plant
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 4
Typical Benefits of DCS
Scalability & Expandability of System
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PEC Islamabad UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 5
Scalability & Expandability of System Improved Control Potential
Improved Operator Interface Capability
Integration of System Function
Single Point Failure
Lower Installation costs
Easy to Maintain
Local Control Unit Architecture
1. It is the smallest collection of hardware ina distributed control system that performs
closed loop control.
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closed loop control.
2. LCU malfunctioning can cause a conditionthat is hazardous to both people and
equipment its proper design is critical
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 6
Typical Requirements of LCU
` Flexibility of changing control configuration
` Ability to use the controller without being expert
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Ability to use the controller without being expert` Ability to bypass the controller in case it fails so
that the process can be controlled manually
` Ability of LCU to communicate with other LCUsand other elements of the system
Architectural Parameters of LCUSize of ControllerFunctionality of Controller
Performance of ControllerCommunication channels out of ControllerController Output Security
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2
Analog inputs
4
Digital Inputs
A LCU
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Capacity:
10 : Continuous
Function Blocks
40: Logic
Function Blocks
LCU A
Analog outputs Digital outputs
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A LCU (Contd)
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.. ..
....
LCU B1
LCU B2
16
Analog inputs
32
Digital Inputs
Capacity:
40 Continuous
Functions Blocks
Capacity:
160 Continuous
Functions Blocks
8
Analog outputs
16
Digital outputs
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Architectural parameters of LCU
` Size of Controller
` Functionality of Controller
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y
` Performance of Controller
` Communication channels out of Controller` Controller Output Security
A large number of configuration are possible
` Single loop
`Two LCU types
` Multiple Loops
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Comment
` Typical cost effectiveness of architectures is
estimated with each of the configuration
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g
` Configuration-A 12 controllers are
required
` Configuration-B 3 controllers + 1 backup
required
` Configuration-C 2 controllers + 1 backup
required
Typical cost effectiveness
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 14
Typical cost effectiveness
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 15
Nos of function blocks in control sys
Control Complexity Ratio
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Nos. of function blocks in control sys
` CCR = --------------------------------------------
Nos. of control system output
Nos. of continuous function blocks
` CCR = ---------------------------------------------
Nos. of control analog output
Fo r com p l e x s y s t e m t h e CCR i s 3 0 - 4 0
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Other Architectural Issues
How long each cable can be extended?
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How many communication channels the
system can support?
What kind of delay is expected?
What is the internal communication system?
Distributed Communication
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Level of Sub networks
Several high level operation interfaces and
communication elements located in the centralcontrol room area must communicate with
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control room area must communicate witheach other at moderate load of messagetraffic.
The message communication has generally three
levels.1. A load bus or subnet
2. A local network in the central control room
3. A plant wide communication
Field-bus Reduces Wirings
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Benefits of Distributed CommunicationA comparison between non-distributed and distributed
Communication facility reveals the following benefits:
Cost of wiring is reduced significantly
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 21
Flexibility of making changes in software &firmware increases
Less time to implement a large control system The control system becomes more reliable due
to significant reduction of physical connection
Typical worries for Distributed CommunicationExisting one-is-to one configuration had notime delay. Sharing the data buses may havesome delay! The answer is NOOverloading of channels!The answer is Overloading may take place.
Requirements of Communication System
1. Minimize time delays and maximized security oftransmission.
2. Communication between various modules and HLHI/
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LLHI should be effective.
3. Communicate set points, operating modes and control
variable from HLHI devices.Additional Requirements
Download control configurations, tuning parametersand user programs for HLHI.
Transmission of information from data input/ outputunits to high level computing devices.
Synchronization of real- time and elements of
machines. Transfer large data for high level processing take trends
and searching applications.
Communication Issues
1. Maximum permitted size of the system
2. Maximum acceptable time3 Maximum allowed delay in systems
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3. Maximum allowed delay in systems
4. Communication rate
5. Rate of undeleted errors occurring in the system ( due tonoise)
6. Sensitivity to traffic loading (traffic of signal load)
7. System scalability (expandable/ large/ small)8. Fault Tolerance (failure of one channel should not effect
other)
9. Interacting requirement (protocol issues RS 232c, RS422, IEEE 488, smart)
10. Ease of application/ maintenance
Smart Hubs In Networks
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 24
Network Topologies
Topology refers to the structure ofphysical connections among the
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PEC Islamabad UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 25
physical connections among theelements in a network.
Some of the popular topologies are:Star
BusMeshRing
Network Topologies (Contd)
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Network Topologies (Contd)
Staris simplest but its failure shall cause theentire sub network to stop functioning
l l b h
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Bustopology is similar to star but the sameproblem exist i. e. sharing one bus
Meshtopology tries to overcome the limitationof star topology and is generally adopted in
industry
Ring or looptopology is a special case ofMash topology that provides connectionsbetween active switching devices in a loopsequence
The Way Ahead-- Management Executive Systems
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6. Februar 2008 / Dr. Ing Naveed Ramzan #
Appied Process Control Systems
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PEC Islamabad UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 1
The Opportunity inStochastic Process
ControlProf. Dr. Shahid Naveed
L ec t u r e - 6
Sequence of Presentation
1.Objective of SPC
2.Basic Concepts of SPC
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3.Techniques & Analysis
4.Common & Special Causes of ProcessDeviations
5.Stable Process
6.Trend Analysis
7.Process Capability
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What statisticscan e calculate
Recalling From Lecture -1 Stochastic gains
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can we calculatefrom this data?
How do we relatevariability to processperformance?
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In Nutshell Squeeze the Variability is the 1st Objective
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 5
Another Example
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 6
2. Basic Concepts for SPC
`What is a process?` Converting raw materials into products
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`What is control?` Achieving the objectives in the desired manner
` Have we done the job correctly?` Only Historic Data can reveal
`Can we do the job more consistently?` Through online statistical monitoring/trend analysis
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SPC Related Queries
Are we doing the job correctly?Detection, prevention, confirmatory to design aspects
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Detection, prevention, confirmatory to design aspects
Can we do the job better?The process and human capability is under question
Can capability/ quality be enhanced?
Through process improvement and training
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3. Techniques & Analysis
` What statisticaltools are
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available?
` Process flowCharts
`
Check or tallycharts
` Histograms
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3. Techniques & Analysis (contd)
` Graphs` Pareto Analysis
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` Pareto Analysis
` Cause & effect
diagrams
` Scatterdiagram
` Control Charts
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What is a Control Chart?
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What is a Control Chart?
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4. Objective of Control Charts
Process monitoring
for extendedperiods
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p
To identify common
causes of processvariation / deviation
To identify special
causes of processvariation/ deviation
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 13
Common Causes of Process Variations
` Inherent or natural variation in the inputs andtransformation activities.
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How to identify them?
` Repeatable, predictable, non- symmetric orrandom.
` Global to the system and originate from manysources.
` Lie within the process band within which a
process is expected to vary.
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 14
Special Causes of Process Variations
` These are variations due to process inputs andtransformation activities that occur irregularly.They are not part of the system but originatefrom outside
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from outside.
How to identify them?
`They are localized to an operator, shift orpiece of equipment.
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Strategy of Process Improvement
` The general policy to improve process
monitoring is to minimize commoncauses and eliminate special causes ofdi t b
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disturbances.
Com m o n Ca u s e s can be minimized by:
` Reduction in variability in inputs andtransformation activities
` Improve the process
` Improve work practices
` Improve operating guidelines
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Strategy of Process Improvement
Sp e c i a l Ca u s e s need to be attended specifically
` Whenever a control chart signals a special
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cause, search immediately for what was done
differently on that instance.` The discovery of special cause of variation is
usually the responsibility of someone who isdirectly connected with the process.
` Do not make a fundamental change inprocess, identify and permanently remove thespecial cause to prevent the recurrence.
` If a special cause can not be pin-pointed makeprocess adjustment.
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 17
5. What is a Stochastic Stable Process ?A Process is said to be in a state of Stochastic Stable Controlif the distribution of measurement data has the same shapelocation and spread over time.In other words, a process is stable when the effects ofall specialcauses have been removedfrom a process, so that the remaining
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p , gvariability is only due to common causes.
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Trend Analysis
Trend Analysis leads to answer the queries like
1. Are we in control ?
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2. Do we continue to be in control ?
and is instrumental to
1. Fault diagnostics
2. Capability enhancement
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Trend Analysis (contd)
After a process is recognized to be out of control
trend analysis is employed to search for thesources of problems.
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 21
The chart is divided into three zones. Zone A isbetween +/- 3. zone B is between +/- 2 andzone C is between +/- 1
The following eight tests can be performed.
Trend Analysis (contd)
Test 1Pattern: One or more points falling outside thecontrol limits on either side of the average.
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 22
Qu
ality
Ch
ara
cte
rist
ics
Problem source:
Equipment breakdownNew OperatorDrastic change in raw materialquality
Change in method, machine,or process settingAction:Go back and look at what
might have been donedifferently before the out ofcontrol point signals.
Trend Analysis (contd)
Test 2Pattern: A run of nine points on one side of the average.
Problem source:This may be due to a small
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 23
This may be due to a smallchange in the level of process
average. This change may bepermanent at the new level.
Action:
Go back to the beginning of therun and determine what wasdone differently at that time orprior to that time
Quality
Characteristics
Trend Analysis (contd)
Test 3Pattern: A trend of six points in a row either increasing or
decreasingProblem Source:
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Qual
ity
Characteristics
Gradual tool wearChange in characteristics suchas gradual deterioration inmixing or concentration of achemical.Deterioration of plating oretching solution in electronicsor chemical industriesAction:Go back to the beginning of therun and search for the sourcein procedure
Trend Analysis (contd)
Test 4:Pattern: Fourteen points in a row alternating up and down within
or outside the control limits.Problem source:
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Quality
Characteristics
Sampling variation fromtwo different sources suchas sampling systematicallyfrom high and low conditionwith two different averages.orAdjustment is being madeall the time (over control).Action: Look for cycles inthe process, such ashumidity or temperaturecycles or operator overcontrol of process
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Trend Analysis (contd)
Test 6Pattern: Four out of five points in a row on one side of the
average in zone B or beyond
Problem source:
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 27
Quality
Characteristics
Problem source:This may be due to a
moderate shift in theprocess
Action: Go back three or
four points in time to findthe root cause.
Trend Analysis (contd)
Test 7Pattern: Fifteen points in a row on either side of the
average in zone CProblem Source:Unnatural small fluctuations or
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 28
Quality
Characteristics
Unnatural small fluctuations orabsence of points near the control
limitsIt may appear to be good controlbut this is not.Incorrect selection of subgroups.
Sampling from various sub-population and combining theminto a single subgroup for chartingIn correct calculation of control
limitsAction: Look very close to thebeginning of the pattern
Trend Analysis (contd)
Test 8Pattern: Eight points in a row on both sides of the center line
with none in zone C.
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Qual
ity
Characteristics
Problem source: No sufficientresolution on the measurementsystem
Action: Look at the range chartand see if it is in control
6. Process Capability
Understanding Capability!
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` Whether the process is capable of meeting the
requirements ?
` Whether the process is meeting the
requirement at any point in time ?
` Can the parameter be corrected or adjusted
when it is not meeting the requirements ?
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 30
Process CapabilityThe capability of a stable process is defined in
terms of a distribution. It is the spread of all
values of the process distribution.Capable Process ( Cp)
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PEC Islamabad UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 31
Cp measures the effect of the inherent variability
Cp is defined mathematically asUSL - LSL
Cp = ---------------6
Allowable process spreadCp = -----------------------------
Actual process spread
Where:USL = upper specification limitLSS: lower specification limit
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Process Capable but not Centered
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The Control implementation is erring towards on lower side.(Or underutilized)
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Centred & Capable Process
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Capability index ( Cpk)The long term objectives of Cpk is to continuously improve
process and reduce variability
Mathematically defined as:
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PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 35
Cpk = Minimum {USL- X / 3, X-LSL/3}
Where X= overall process averageCpk is applicable for process centering.
If for a two sided specification the capability index (Cpk) isequal to or greater than 1.33, then the process may beadequately centered.
Cpk may be employed even when there is only one sidedspecification. This is used to determine the percentage ofobservations out of specification.
` A process is capable (Cp1) if its naturaltolerance lies within the engineering tolerance
Capability index ( Cpk) (contd)
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or specifications. The measure of process
capability of a stable process is 6 where isthe inherent process variability estimated fromthe process.
` A minimum value of Cp = 1.33 is generallyused for an on going process. This ensures avery low reject rate of 0.007% and thereforeis an effective strategy for prevention ofnonconforming items.
PEC UET Lahore Dr. Shahid Naveed 9. April 2009 / Dr. Ing Naveed Ramzan 36
Conclusion
Stochastic Process Control has greatOpportunities leading to Production,
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Opportunities leading to Production,Quality Assurance, Fault Diagnostics,
Capability Enhancement etc.
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