PCS MIDTERM

Question 1

Controller in automatic, control valve is 100% open and the PV is increasing

Answer 1

Open, m not varying based on feedback from PV

Question 2

Controller in automatic, SP = 50°C, PV is steady around 50°C

Answer 2

Closed, PV is being maintained at SP

Question 3

Fired, flying bullet

Answer 3

Open, flight of bullet doesn’t change if target moves

Question 4

Feedback

Answer 4

A control scheme where the controlled variable is measured and compared to a desired value then a signal is sent to a final control element that manipulates some physical variable, this happens automatically.

Question 5

b) Feedforward

Answer 5

A control scheme that measures a load and based on a model calculates a signal to the final control element in order to maintain the controlled variable at some desired value. In pure feedforward there is no measurement of the controlled variable.

Question 6

c) Open loop

Answer 6

A type of control system that uses only an input signal to actuate an output. There is no automatic feedback to adjust the process, so adjustments must be made manually by the operator or the output is preset.

Question 7

d) Closed loop

Answer 7

A type of control system that automatically changes the output based on the difference between the feedback signal to the input signal.

Question 8

e) On-off

Answer 8

A type of controller or final control element that has only 2 states e.g. on/off, start/stop,
open/close, energize/denergize. There is no intermediate state.

Question 9

f) Modulating

Answer 9

A type of controller or final control element that can be at a value or position 0 to 100%
inclusive.

Question 10

g) Saturation

Answer 10

The condition of a controller or final control element when it is at a maximum or minimum value of it range or travel.

Question 11

h) AUTO mode

Answer 11

In the operation sense the mode of the controller that results in feedback loop working automatically. The controller has to be in AUTO for the loop to be closed. It is possible for the controller in AUTO and the loop is open. The operator can set the SP, the OP can’t be changed.

Question 12

i) MAN mode

Answer 12

In the operation sense the mode of the controller that results in the loop being open. The operator can set the OP, the SP can’t be changed.

Question 13

j) SP Tracking

Answer 13

When the controller is in MAN the SP is forced equal to the PV so that there is no bump in controller output when the mode is switched back to AUTO.

Question 14

following devices as modulating or on-off?
a) Automobile cruise control

Answer 14

Modulating

Question 15

following devices as modulating or on-off?
b) Light switch

Answer 15

ON-OFF

Question 16

following devices as modulating or on-off?
c) Kitchen water faucet

Answer 16

Modulating

Question 17

following devices as modulating or on-off?
d) Home electric fan

Answer 17

An interesting case, usually a fan has slow/medium/fast/off setting. So it is a 4 state device.
Definitely not modulating, but technically not on-off because it isn’t 2 states.

Question 18

In some processes the controlled variable deviated from the set point because of disturbances, regulatory control refers to systems designed to compensate for these disturbances.

Answer 18

Regulatory control

Question 19

In some processes, the most important disturbance is the set point itself. That is, the set point may be changed as a function of time. Servo control refers to control systems designed for this purpose.

Answer 19

Servo control (or supervisory)

Question 20

A control loop is open when

Answer 20

the controlled variable (i.e. process output) has no influence on the manipulated variable (i.e. process input).

Question 21

A control loop is closed when

Answer 21

the controlled variable (i.e. process output) has an influence on the manipulated variable (i.e. process input).

Question 22

An operator decides to put a controller into manual mode. Which of the following statements is true?

Answer 22

Loop is open.

Question 23

Which statement describes the manipulated variable in a feedback control?

Answer 23

The variable that is adjusted in order to maintain the controlled variable at the setpoint.

Question 24

A system designed to shed load disturbances.

Answer 24

regulatory control