Final

Question 1

What are open-loop control systems?

Answer 1

they have no negative feedback (feedback from output to input)

Question 2

What are closed-loop control systems?

Answer 2

systems that have negative feedback path (from output to input)

Question 3

What does a typ. closed-loop control system look like?

Answer 3

Input (Setpoint) - Controller - FCE - Process - Output
I I
- Measurement -

Question 4

What is the difference between a transmitter and transducer?

Answer 4

• a transducer is a device which receives information in the form of one quantity and converts it to information in the form of the same or another quantity
• a transmitter is a transducer that responds to a measured variable by means of a sensing element and converts it to a standardized transmission signal which is a function only of the measured variable

Question 5

What is the difference between pneumatic and electronic signals?

Answer 5

• pneumatic signals use pressure of a gas (air) to carry signal information
• electronic signals use electrical voltage or current to carry signal information

Question 6

What are the common pneumatic signals?

Answer 6

20-100 kPag
3-15 Psig

Question 7

What are the common electronic signals?

Answer 7

1-5 V
4-20 mA

Question 8

What are the different types of errors in transducers?

Answer 8

1) Bias error
2) Span error
3) Linearity error
4) Repeatability
5) Resolution

Question 9

Define Control Variable:

Answer 9

the condition which is being regulated or maintained

Question 10

Define Measured Variable:

Answer 10

the condition that yields information about the controlled variable

Question 11

Define Uncontrolled Variable:

Answer 11

any condition that can affect the controlled variable but itself is uncontrolled

Question 12

Define Manipulated Variable:

Answer 12

condition that is being adjusted to regulate or maintain the controlled variable

Question 13

Define Load Variable

Answer 13

a special type of uncontrolled variable that affects the mass or energy of a process and which the manipulated variable is directly countering

Question 14

Define Setpoint:

Answer 14

the desired condition of the controlled variable

Question 15

Define Error:

Answer 15

the difference between the desired condition and the actual condition of the measured variable

Question 16

What are the control system objectives?

Answer 16

1) minimize settling time
2) minimal peak error
3) minimal residual error

Question 17

What is transfer lag?

Answer 17

product of resistance and capacitance
- capacitance: the ability any control system component to store mass or energy
- resistance: the opposition to the flow of mass or energy by any control system component

Question 18

What is transport lag?

Answer 18

the distance/velocity lag found wherever a mass is transported over a distance (the length of time required to travel the distance)

Question 19

What are the different types of strain?

Answer 19

• axial strain (delta L/L)
• lateral strain (delta d/d)

Question 20

Define the relationship between stress and strain:

Answer 20

strain is directly proportional to the stress applied

Question 22

List seven flow measurement systems:

Answer 22

1) Head type flowmeters
2) Variable area flowmeter (rotameter)
3) Turbine flowmeter
4) Vortex shedding flowmeter
5) Magnetic flowmeter
6) Coriolis flowmeter
7) Ultrasonic flowmeter

Question 23

List some Head Type flowmeters:

Answer 23

1) Orifice Plate
2) Venturi
3) Pitot tube

Question 24

List some Ultrasonic flowmeters:

Answer 24

1) Transit time
2) Doppler

Question 25

What is the difference between gauge and absolute pressure and how does it affect a reading?

Answer 25

- gauge pressure is with respect to atmospheric pressure while absolute pressure is with respect to absolute zero pressure - gauge is affected by elevation while absolute is not - if elevation is increased atmospheric is decreased and gauge is decreased, but absolute stay the same

Question 26

List some pressure gauge protection devices:

Answer 26

1) Pigtail/Siphon 2) Safety blowout 3) Oil filled case 4) snubber 5) chemical seal/diaphragm seal

Question 27

What does a safety blowout do?

Answer 27

it vents process fluid away from the front of the gauge to prevent gauge glass from breaking (away from glass and blowout from back)

Question 28

What does an oil filled case do?

Answer 28

filling the gauge with oil dampens mechanical vibrations, making the gauge easier to read and extending its service life

Question 29

What does a snubber do?

Answer 29

used to dampen/restrict pressure fluctuations which could wear out the gauge and make it difficult to read

Question 30

What is a chemical seal/Diaphragm seal used for?

Answer 30

it is placed between the gauge and the process fluid to help extend the gauge service life in case where the fluid is corrosive or to prevent fluid from plugging the sensing element

Question 31

What is a pigtail or siphon?

Answer 31

they prevent high temperature steam from entering the bourdon tube by forming a condensate buffer, isolating the high temp. steam from the gauge (to avoid degradation in gauge performance)

Question 32

List some Direct Level Measurement Methods:

Answer 32

1) Dipstick 2) Sightglass 3) Constant Displacement Float and Tape System

Question 33

List some Inferential Level Measurement Methods:

Answer 33

1) Ultrasonic Level Measurement 2) Microwave/Radar Level Measurement 3) Capacitance Level Measurement 4) Nuclear Level Measurement 5) Variable Displacement Float System 6) Hydrostatic Level Measurement 7) Open Tank Measurements

Question 34

List the three common temp. transducers (w/ definitions):

Answer 34

1) RTD (Resistance Temp. Detectors): measures change in resistance - linear 2) Thermistor: measures change in resistance - non-linear 3) Thermocouple: creates a small voltage based on temp. difference

Question 35

List some applications for pitot tube:

Answer 35

- measure airspeed (planes) - HVAC systems - formula one cars

Question 36

What are some adv. and disadv. for a rotameter?

Answer 36

Adv.: - direct indication of flow - low cost - low pressure drop - no power required Disadv.: - must be mounted vertically - easily breaks - fluid must be clean - sensitive to fluid density

Question 37

What are some adv. and disadv. for turbine flowmeter?

Answer 37

Adv.: - high accuracy - repeatable measurement Disadv.: - high cost - moving parts - not good for low flow

Question 38

What is an application example for turbine flowmeters?

Answer 38

oil & has blending

Question 39

What are some adv. and disadv. for vortex shedding flowmeter?

Answer 39

Adv.: - no moving parts - good accuracy Disadv.: - not suitable for dirty, abrasive fluids - not suitable for laminar flow - midrange, expensive

Question 40

What are some adv. and disadv. for magnetic flowmeter?

Answer 40

Adv.: - no restriction of flow - very accurate Disadv.: - only works for conductive fluids

Question 41

What are some adv. and disadv. for coriolis flowmeter?

Answer 41

Adv.: - highest accuracy Disadv.: - not good for slurries - expensive

Question 42

What are some adv. and disadv. for ultrasonic flowmeters?

Answer 42

Adv.: - simple construction - easy to install - can handle corrosive fluid Disadv.: - disturbed by electrical noise easily - build up on pipe wall affects the reading

Question 43

List some strain gauge applications:

Answer 43

1) Weighing scales 2) Electronic scales 3) Bicycle power meters 4) To measure strain placed on components of buildings