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3442 Industrial Instruments 2 Chapter 12 Control-Loop Characteristics Dr. Bassam Kahhaleh Princess Sumaya Univ. Electronic Engineering Dept.

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Presentation on theme: "3442 Industrial Instruments 2 Chapter 12 Control-Loop Characteristics Dr. Bassam Kahhaleh Princess Sumaya Univ. Electronic Engineering Dept."— Presentation transcript:

1 3442 Industrial Instruments 2 Chapter 12 Control-Loop Characteristics Dr. Bassam Kahhaleh Princess Sumaya Univ. Electronic Engineering Dept.

2 Princess Sumaya University Industrial Instruments 22 / 19 12: Control-Loop Characteristics Control System Configurations Single Variable Single Variable Independent Single Variable Independent Single Variable Flow rate Regulation

3 Princess Sumaya University Industrial Instruments 23 / 19 12: Control-Loop Characteristics Control System Configurations Single Variable Single Variable Independent Single Variable Independent Single Variable Interactive Single Variable Interactive Single Variable Flow rate Regulation TemperatureRegulation

4 Princess Sumaya University Industrial Instruments 24 / 19 12: Control-Loop Characteristics Control System Configurations Single Variable Single Variable Independent Single Variable Independent Single Variable Interactive Single Variable Interactive Single Variable Compound Variable Compound Variable Example: Maintain A : B = 3 : 5

5 Princess Sumaya University Industrial Instruments 25 / 19 12: Control-Loop Characteristics Control System Configurations Cascade Control Cascade Control

6 Princess Sumaya University Industrial Instruments 26 / 19 12: Control-Loop Characteristics Control System Configurations Cascade Control Cascade Control Example:

7 Princess Sumaya University Industrial Instruments 27 / 19 12: Control-Loop Characteristics Multivariable Control Systems Analog Control Analog 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.

8 Princess Sumaya University Industrial Instruments 28 / 19 12: Control-Loop Characteristics Multivariable Control Systems Analog Control Analog Control Supervisory & Direct Digital Control (DDC) Supervisory & Direct Digital Control (DDC) May use self-adapting algorithms.

9 Princess Sumaya University Industrial Instruments 29 / 19 12: Control-Loop Characteristics Control System Quality Definition of Quality Definition of Quality Loop Disturbance Loop Disturbance Quality: the degree to which the deviations that result from the disturbances are minimized. Types: 1. Transient 2. Setpoint changes 3. Load change

10 Princess Sumaya University Industrial Instruments 210 / 19 12: Control-Loop Characteristics Control System Quality Definition of Quality Definition of Quality Loop Disturbance Loop Disturbance Optimum Control Optimum Control Quality: 1. Stability 2. Minimum deviation 3. Minimum duration

11 Princess Sumaya University Industrial Instruments 211 / 19 12: Control-Loop Characteristics Control System Quality Measure of Quality Measure of Quality Overdamped Overdamped Critically Damped Critically Damped Underdamped Underdamped Quarter Amplitude Quarter Amplitude Minimum Area Minimum Area

12 Princess Sumaya University Industrial Instruments 212 / 19 12: Control-Loop Characteristics Stability Stability Criteria Stability Criteria A system is stable if the phase lag is less than 180° at the frequency for which the gain is unity. A system is stable if the phase lag is less than 180° at the frequency for which the gain is unity. A system is stable if the gain is less than one at the frequency for which the phase lag is 180 ° A system is stable if the gain is less than one at the frequency for which the phase lag is 180 °

13 Princess Sumaya University Industrial Instruments 213 / 19 12: Control-Loop Characteristics Process Loop Tuning Open-Loop Transient Response Method Open-Loop Transient Response Method Known as Process-Reaction Method Known as Process-Reaction Method Only for systems with self-regulation Only for systems with self-regulation 1.Open the loop (No feedback) by disconnecting the controllers output from the final element. 2.Introduce a transient disturbance by a small, manual change of the controlling variable using the final control element. 3.Measure the controlled variable (record it versus time).

14 Princess Sumaya University Industrial Instruments 214 / 19 12: Control-Loop Characteristics Process Loop Tuning Open-Loop Transient Response Method Open-Loop Transient Response Method L: lag time in minutes N: reaction time (%/min)

15 Princess Sumaya University Industrial Instruments 215 / 19 12: Control-Loop Characteristics Process Loop Tuning Open-Loop Transient Response Method Open-Loop Transient Response Method Proportional Mode: ¼ Amplitude: Proportional-Integral Mode: ¼ Amplitude:

16 Princess Sumaya University Industrial Instruments 216 / 19 12: Control-Loop Characteristics Process Loop Tuning Ziegler-Nichols Method Ziegler-Nichols Method Known as Ultimate Cycle Method Known as Ultimate Cycle Method 1.Reduce any integral and derivative actions to their minimum effect. 2.Gradually begin to increase the proportional gain while providing periodic small disturbances to the process. 3.Note the gain K C at which the dynamic variable just begins to exhibit steady cycling (oscillations about the setpoint). 4.Note the critical period T C of these oscillations

17 Princess Sumaya University Industrial Instruments 217 / 19 12: Control-Loop Characteristics Process Loop Tuning Ziegler-Nichols Method Ziegler-Nichols Method Proportional Mode: Proportional-Integral Mode:

18 Princess Sumaya University Industrial Instruments 218 / 19 12: Control-Loop Characteristics Process Loop Tuning Frequency Response Method Frequency Response Method 1.If the phase lag is less than 140° at the unity gain frequency, the system is stable. 2.If the gain is 5 dB below unity (gain = 0.56) when the phase lag is 180°, the system is stable.

19 Princess Sumaya University Industrial Instruments 219 / 19 12: Control-Loop Characteristics End of Chapter 12


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