Chapter 37

Question 1

What is controller tuning?
Controller tuning is the____ determining the tuning _______ for the PID controller _______ gain, ________time, and _______ time to obtain a desired controller response to process disturbances.

Answer 1

What is controller tuning?
Controller tuning is the__process__ determining the tuning _____coefficients___ for the PID controller ______proportional_ gain, _____integral___time, and _______derivative_ time to obtain a desired controller response to process disturbances.

Question 2

What are common concerns with controller tuning?
1._______ the______ tuning
coefficients,
2._______ appropriate ________standards.
3. Using _______ controller
4. ______a _______ tuning method.

Answer 2

Common concerns with controller tuning are
1.Selecting the proper tuning
coefficients,
2.Developing appropriate performance standards.
3. Using self-tuning controller
4. Choosing a manual tuning method.

Question 3

What is the symbol for controller gain?

Answer 3

(Kc)

Question 4

What is the symbol for Proportional gain?

Answer 4

(Kp)

Question 5

What is the symbol forProportional Band?

Answer 5

(PB)

Question 6

What is the symbol for Reset Rate?

Answer 6

(T1)

Question 7

What is the symbol for Reset Gain?

Answer 7

(R1)

Question 8

What is the symbol for Reset Gain?

Answer 8

(K1)

Question 9

What is the symbol for Derivative Time?

Answer 9

(TD)

Question 10

What is the symbol for Derivative gain?

Answer 10

(KD)

Question 11

What are performance standards?

Performance Standards are a way of measuring the effectiveness of controller tuning and controller action.

Answer 11

Performance Standards are a way of measuring the effectiveness of controller tuning and controller action.

Question 12

What is a Performance Standard defined as?

Answer 12

A closed loop response of a second-order system.

Question 13

What are the three common controller Performance Standards?

Answer 13

1. Decay Ratio
2. Overshoot
3. Dead Time

Question 14

Explain Decay Ratio

Answer 14

Decay Ratio-
Is a measurement of how quickly an overshoot decays from one oscillation to the next as the controller brings the process to the setpoint.

Question 15

What is the most common Decay Ratio Performance Standard?

Answer 15

The One-Quarter Decay Ratio

Question 16

Explain One-quarter decay ratio.

Answer 16

One-Quarter Decay Ratio-
Is a response where the amount of overshoot decays to one-fourth of the previous amplitude of the overshoot every whole cycle after being upset by a disturbance.

Question 17

Why is the one-quarter decay ratio so popular?

Answer 17

It is very easy to judge when it is obtained.

Question 18

Explain overshoot

Answer 18

Overshoot-
Is the change of a process variable (PV) that exeeds the upper dead band value when there is a disturbance to the system.

Question 19

Define Dead Time.

Answer 19

Dead Time-
Is the period of time that occurs between the time a change is made to a process and the time the first response to that change is detected.

Question 20

Explain Rise Time.

Answer 20

Rise Time-

The length of time required for a PV to cross the ultimate value after a step input change, such as the setpoint change.

Question 21

Explain Dynamic Response Time.

Answer 21

Dynamic Response Time-

The length of time required for a PV to remain within 5% of its ultimate value following a step input change.

Question 22

Explain Gain Margin.

Answer 22

Gain Margin-
The factor by which controller gain may be increased before instability occurs and therefore is a measure of relative stability.

Question 23

Explain Self-tuning Controller.

Answer 23

Self-tuning Controller-
A controller that has built-in algorithms or pattern recognition techniques that periodically test the process and make changes to the controller tuning settings while the process is operating.

Question 24

Explain Stand-alone Controller.

Answer 24

Stand-alone Controller-
A controller that has its powers supplies, input signal processing, controller functions, input signals, and displays contained in the same case.

Question 25

What are the three pretuning checks that must be made to a control loop prior to placing it in operation. 1. 2. 3.

Answer 25

1. First ensure that the controller action, direct or reverse, is selected correctly. 2. Second, determine which controller functions are needed for the process. 3. Third, determine the initial tuning values that are to be used for the chosen controller functions.

Question 26

Explain the Setpoint Step Change Method.

Answer 26

Setpoint Step Change Method- | A manual tuning method that consists of making small changes in the setpoint and observing the responses.

Question 27

What are the six steps to tune a controller with the Setpoint Step Change Method?

Answer 27

1. The controller must be in auto mode and the measurement should be steady. 2. Start by adjusting the proportional gain. 3. Repeat step 2 until the controller response is satisfactory. 4. At this point integral time can be adjusted. 5. Repeat step 4 until the controller is satisfactory. 6. If a derivative function is needed in the controller, we it to a value in minutes no larger that the integral time.

Question 28

Explain the Tuning Map Method.

Answer 28

Tuning Map Method- | A procedure that compares process curves to one of numerous typical closed loop[ response curves.

Question 29

What are the advantages and disadvantages of the | Tuning Map Method?

Answer 29

The advantage of this method is that all the controller parameters can be adjusted at the same time. The disadvantage of this method is that it can be very difficult to match the present controller response to the correct response on the tuning maps.

Question 30

What is the most common tuning methods?

Answer 30

The most common tuning methods are the 1. Zieglar-Nichols open-loop tuning method or the 2.process reaction curve method and the 3. Zieglar-Nichols closed-loop tuning method or ultimate period method. Both methods make changes to the process and measure process parameters related to how the system responds to the changes.

Question 31

Explain Zieglar-Nichols Closed-loop Tuning.

Answer 31

Zieglar-Nichols Closed-loop Tuning- | A method of tuning a controller by increasing the gain until the system cycles at the point of instability.

Question 32

What is Ultimate Gain?

Answer 32

Ultimate Gain- | Is a closed loop proportional gain at the point of oscillation.

Question 33

What is Ultimate Period?

Answer 33

Ultimate Period- | The closed-loop cycle time at the point of oscillation.

Question 34

Explain Zieglar-Nichols Open-loop Tuning

Answer 34

Zieglar-Nichols Open-loop Tuning- | A method of tuning a controller based on open loop response to a step input.

Question 35

What is an advantage of Zieglar-Nichols Open-loop Tuning?

Answer 35

An advantage of this method is that it is safer than the closed loop method because it does not force the process into oscillation.

Question 36

What is an disadvantage of Zieglar-Nichols Open-loop Tuning?

Answer 36

A disadvantage is that it is sometimes difficult to identify all the key parameters with enough accuracy to establish the correct tuning values.