Closed-Loop System

Question 1

Change in any variable that may cause the controlled variable of the process to change

Answer 1

Load

Question 2

Desired value of the controlled variable

Answer 2

Set point

Question 3

Negative Error, 𝜀 formula

Answer 3

𝜀 = 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑣𝑎𝑙𝑢𝑒 − 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑣𝑎𝑙𝑢𝑒

Question 4

If the load value increases, the process and measured values will also increase, making the error even more positive.

Answer 4

Positive feedback

Question 5

If the load value increases, the process and measured values will also increase, making the error negative.

Answer 5

Negative feedback

Question 6

Assume no change in the load.

The set point would be changed in accordance with the desired variation.

Answer 6

Servo problem

Question 7

Assume no change in set point.

There will be an importance in maintaining the controlled variable in spite of changes in load.

Answer 7

Regulator problem

Question 8

Moves the valve stem as the pressure on a spring-loaded diaphragm changes

Answer 8

Pneumatic device (valve motor)

Question 9

Positions of a plug in the orifice of the valve body

Answer 9

Stem

Question 10

As the air pressure increases, the plug moves downward and restricts the flow of fluid through the valve

Answer 10

Air-to-close valve

Question 11

The valve opens and allows greater flow as the valve-top air pressure increases

Answer 11

Air-to-open valve

Question 12

Often constructed so that the valve stem position is proportional to the valve-top pressure

Answer 12

Valve motor

Question 13

Fluid flow is proportional to the valve-top pneumatic pressure at steady-state

Answer 13

Linear valve

Question 14

Means that stem position does not respond instantaneously to a change in the applied pressure from the controller (pneumatic valve always has dynamic lag)

Answer 14

Dynamic lag

Question 15

Inserted into the controller so that the error reaches some finite positive value before the controller “turns on.”

Answer 15

Dead band

Question 16

A phenomenon where the controller will rapidly cycle on and off as the error fluctuates about zero

Answer 16

Phenomenon of chattering

Question 17

Additional control mode introduced if we cannot tolerate any residual error
Integral mode ultimately drives the error to zero

Answer 17

Integral control

Question 18

The reciprocal of (tau_integral)

Answer 18

Reset rate

Question 19

Acts upon the derivative of the error, so it is most active when the error is changing rapidly.

Answer 19

PD control

Question 20

Other terms used to describe derivative action

Answer 20

• Rate Control
• Anticipatory control

Question 21

Based on how rapidly the error is changing, not the magnitude of the error or how long the error has persisted.

Answer 21

Derivative action

Question 22

Cause significant problems for derivative action because of the rapidly changing slope of the error caused by noise.

Answer 22

“Noisy” error signals

Question 23

Defined as one for which the output response is bounded for all bounded inputs (BIBO)

Answer 23

Stable system

Question 24

System exhibiting an unbounded response to a bounded input

Answer 24

Unstable system

Question 25

Minimum or maximum limit value

Answer 25

Saturation

Question 26

A linear control system is unstable if any roots of its characteristic equation are on, or to the right of, the imaginary axis. Otherwise, the system is stable.

Answer 26

Stability for linear systems