3442 3442 Industrial Instruments Industrial Instruments 2 2 Chapter 12 Chapter 12 Control-Loop Control-Loop Characteristics Characteristics Dr. Bassam Kahhaleh Dr. Bassam Kahhaleh Princess Sumaya Princess Sumaya Univ. Univ. Electronic Engineering Dept. Electronic Engineering Dept.
3442 Industrial Instruments 2 Chapter 12 Control-Loop Characteristics Dr. Bassam Kahhaleh Princess Sumaya Univ. Electronic Engineering Dept.
Mar 30, 2015
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34423442Industrial Instruments 2Industrial Instruments 2
Chapter 12Chapter 12Control-Loop CharacteristicsControl-Loop Characteristics
Dr. Bassam KahhalehDr. Bassam Kahhaleh
Princess Sumaya Univ.Princess Sumaya Univ.Electronic Engineering Dept.Electronic Engineering Dept.
Princess Sumaya UniversityPrincess Sumaya University 3442 - Industrial Instruments 23442 - Industrial Instruments 2 22 / 19 / 19
12: Control-Loop Characteristics12: Control-Loop CharacteristicsControl System ConfigurationsControl System Configurations Single VariableSingle Variable
Independent Single VariableIndependent Single Variable
Flow rate RegulationFlow rate Regulation
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsControl System ConfigurationsControl System Configurations Single VariableSingle Variable
Independent Single VariableIndependent Single Variable Interactive Single VariableInteractive Single Variable
Flow rateFlow rateRegulationRegulation
TemperatureTemperatureRegulationRegulation
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsControl System ConfigurationsControl System Configurations Single VariableSingle Variable
Independent Single VariableIndependent Single Variable Interactive Single VariableInteractive Single Variable Compound VariableCompound Variable
Example:Maintain A : B = 3 : 5
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsControl System ConfigurationsControl System Configurations Cascade ControlCascade Control
Princess Sumaya UniversityPrincess Sumaya University 3442 - Industrial Instruments 23442 - Industrial Instruments 2 66 / 19 / 19
12: Control-Loop Characteristics12: Control-Loop CharacteristicsControl System ConfigurationsControl System Configurations Cascade ControlCascade Control
Example:
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsMultivariable Control SystemsMultivariable Control Systems Analog ControlAnalog Control
Example:In a reaction vessel, two reactants are mixed, react, and the product is drawn from the bottom. The reaction rate is to be controlled.
It is also important to keep the reaction temperature and vessel pressure below certain limits&The level is to be controlled at some nominal value.
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsMultivariable Control SystemsMultivariable Control Systems Analog ControlAnalog Control Supervisory & Direct Digital Control (DDC)Supervisory & Direct Digital Control (DDC)
May use May use self-adaptingself-adapting algorithms. algorithms.
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsControl System QualityControl System Quality Definition of QualityDefinition of Quality
Loop DisturbanceLoop DisturbanceQualityQuality: the degree to which the deviations that result from : the degree to which the deviations that result from
the disturbances are minimized.the disturbances are minimized.
TypesTypes: 1. Transient: 1. Transient
2. Setpoint changes2. Setpoint changes
3. Load change3. Load change
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsControl System QualityControl System Quality Definition of QualityDefinition of Quality
Loop DisturbanceLoop Disturbance Optimum ControlOptimum ControlQualityQuality: 1. Stability: 1. Stability
2. Minimum deviation2. Minimum deviation
3. Minimum duration3. Minimum duration
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsControl System QualityControl System Quality Measure of QualityMeasure of Quality
OverdampedOverdamped Critically DampedCritically Damped UnderdampedUnderdamped Quarter AmplitudeQuarter Amplitude Minimum AreaMinimum Area
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsStabilityStability Stability CriteriaStability Criteria
A system is stable if the phase lag is less A system is stable if the phase lag is less than 180° at the frequency for which the gain than 180° at the frequency for which the gain is unity.is unity.
A system is stable if the gain is less than one A system is stable if the gain is less than one at the frequency for which the phase lag is at the frequency for which the phase lag is 180 °180 °
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsProcess Loop TuningProcess Loop Tuning Open-Loop Transient Response MethodOpen-Loop Transient Response Method
Known as Known as Process-ReactionProcess-Reaction Method Method Only for systems with self-regulationOnly for systems with self-regulation
1.1. Open the loop (No feedback) by disconnecting Open the loop (No feedback) by disconnecting the controller’s output from the final element.the controller’s output from the final element.
2.2. Introduce a transient disturbance by a small, Introduce a transient disturbance by a small, manual change of the controlling variable using manual change of the controlling variable using the final control element.the final control element.
3.3. Measure the controlled variable (record it versus Measure the controlled variable (record it versus time).time).
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsProcess Loop TuningProcess Loop Tuning Open-Loop Transient Response MethodOpen-Loop Transient Response Method
LL: lag time in minutes: lag time in minutes
NN: reaction time (%/min): reaction time (%/min)
T
CpN
Cp
NLR
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsProcess Loop TuningProcess Loop Tuning Open-Loop Transient Response MethodOpen-Loop Transient Response Method
Proportional Mode:Proportional Mode:
NL
PKP
Cp
NL
NL
PKP
3
11¼ Amplitude:¼ Amplitude:
Proportional-Integral Mode:Proportional-Integral Mode:
LK
NL
PK
t
P
33.31
9.0
R
R
K
RNL
PK
t
P
209
3301
12
19.0
¼ Amplitude:¼ Amplitude:
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsProcess Loop TuningProcess Loop Tuning Ziegler-Nichols MethodZiegler-Nichols Method
Known as Known as Ultimate Cycle Ultimate Cycle MethodMethod1.1. Reduce any integral and derivative actions to Reduce any integral and derivative actions to
their minimum effect.their minimum effect.
2.2. Gradually begin to increase the proportional gain Gradually begin to increase the proportional gain while providing periodic small disturbances to while providing periodic small disturbances to the process.the process.
3.3. Note the gain Note the gain KKCC at which the dynamic variable at which the dynamic variable
just begins to exhibit steady cycling (oscillations just begins to exhibit steady cycling (oscillations about the setpoint).about the setpoint).
4.4. Note the critical period Note the critical period TTCC of these oscillations of these oscillations
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsProcess Loop TuningProcess Loop Tuning Ziegler-Nichols MethodZiegler-Nichols Method
Proportional Mode:Proportional Mode:
CP KK 5.0
Proportional-Integral Mode:Proportional-Integral Mode:
2.1
1
45.0
C
t
CP
T
K
KK
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12: Control-Loop Characteristics12: Control-Loop CharacteristicsProcess Loop TuningProcess Loop Tuning Frequency Response MethodFrequency Response Method
1.1. If the phase lag is less than 140° at the unity If the phase lag is less than 140° at the unity gain frequency, the system is stable.gain frequency, the system is stable.
2.2. If the gain is 5 dB below unity (gain = 0.56) If the gain is 5 dB below unity (gain = 0.56) when the phase lag is 180°, the system is when the phase lag is 180°, the system is stable.stable.
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12: Control-Loop Characteristics12: Control-Loop Characteristics
End of Chapter 12End of Chapter 12
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