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

2. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Control System Configurations
Single Variable
Independent Single Variable
Flow rate Regulation
Dr. Bassam Kahhaleh

3. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Control System Configurations
Single Variable
Independent Single Variable
Interactive Single Variable
Flow rate
Regulation
Temperature
Regulation
Dr. Bassam Kahhaleh

4. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Control System Configurations
Single Variable
Independent Single Variable
Interactive Single Variable
Compound Variable
Example:
Maintain A : B = 3 : 5
Dr. Bassam Kahhaleh

5. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Control System Configurations
Cascade Control
Dr. Bassam Kahhaleh

6. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Control System Configurations
Cascade Control
Example:
Dr. Bassam Kahhaleh

7. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Multivariable Control Systems
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.
Dr. Bassam Kahhaleh

8. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Multivariable Control Systems
Analog Control
Supervisory & Direct Digital Control (DDC)
May use self-adapting algorithms.
Dr. Bassam Kahhaleh

9. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Control System Quality
Definition of Quality
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
Dr. Bassam Kahhaleh

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

11. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Control System Quality
Measure of Quality
Overdamped
Critically Damped
Underdamped
Quarter Amplitude
Minimum Area
Dr. Bassam Kahhaleh

12. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Stability
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 gain is less than one at the frequency for which the phase lag is 180 °
Dr. Bassam Kahhaleh

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

14. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Process Loop Tuning
Open-Loop Transient Response Method
L: lag time in minutes
N: reaction time (%/min)
Dr. Bassam Kahhaleh

15. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Process Loop Tuning
Open-Loop Transient Response Method
Proportional Mode:
¼ Amplitude:
Proportional-Integral Mode:
¼ Amplitude:
Dr. Bassam Kahhaleh

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

17. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
Process Loop Tuning
Ziegler-Nichols Method
Proportional Mode:
Proportional-Integral Mode:
Dr. Bassam Kahhaleh

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

19. 12: Control-Loop Characteristics
Princess Sumaya University
Industrial Instruments 2
12: Control-Loop Characteristics
End of Chapter 12