Chapter 9

Question 1

refers to the interface between the physical process and the controller.

Answer 1

instrumentation in process control

Question 2

instrumentations includes

Answer 2

measurement of controlled variable (CV)
manipulation of the manipulated variable (MV)
signal transmission between components

Question 3

types of signal transmission

Answer 3

pneumatic signals (3-15 psig)
analog electronic signals (4-20 mA, 1-5 VDC)
digital signals

Question 4

type of signal transmission that was used before 1960s

Answer 4

pneumatic signals

Question 5

type of signal transmission that is preferred due to noise immunity and long-distance transmission

Answer 5

analog electronic signal

Question 6

type of signal transmission that enable smart sensors with diagnostics and memory

Answer 6

digital signals

Question 7

is a digital communication network for instrumentation and control equipment.

Answer 7

fieldbus

Question 8

what does the fieldbus do?

Answer 8

Reduces wiring, allows multiple instruments on one cable.

Question 9

variants of fieldbus that offer flexibility but introduce challenges like power and security.

Answer 9

wireless variants

Question 10

examples of fieldbus systems

Answer 10

Foundation Fieldbus
Profibus
HART
Modbus

Question 12

detects physical variables and converts them to electrical or mechanical signals.

Answer 12

sensor

Question 13

what sensor type measures temperature

Answer 13

thermocouple, RTD

Question 14

what sensor type measures pressure

Answer 14

strain-gauge, DP cell

Question 15

what sensor type measures flow

Answer 15

orifice, coriolis

Question 16

what sensor type measures level

Answer 16

radar, ultrasonic

Question 17

what sensor type measures composition

Answer 17

pH, GC, IR

Question 18

static property: closeness to true value

Answer 18

accuracy

Question 19

static property: reproducibility

Answer 19

precision

Question 20

static property: smallest detectable change

Answer 20

resolution

Question 21

static property: systematic offset

Answer 21

bias

Question 22

static property: operating limits of the sensor

Answer 22

range/span

Question 23

dynamic property that should be ≤ 10% of the process time constant for minimal lag

Answer 23

time constant

Question 24

are devices that act on the process to modify the manipulated variable (e.g., flow, heat input)

Answer 24

Final Control Elements

Question 25

These are critical for ensuring the desired process response and stability.

Answer 25

Final Control Elements

Question 26

examples of Final Control Elements

Answer 26

control valves, electric heaters, variable-speed drives

Question 27

Final Control Elements must be

Answer 27

carefully sized, selected, and maintained

Question 28

regulate fluid flow by changing the orifice opening via the movement of a stem and plug.

Answer 28

control valves

Question 29

major components of control valves:

Answer 29

actuator, stem, plug, seat, body

Question 30

component of control valve that may be pneumatic or electric

Answer 30

actuator

Question 31

component of control valve that connects actuator to plug

Answer 31

stem

Question 32

component of control valve that moves to change flow rate

Answer 32

plug

Question 33

component of control valve that has a fixed surface for sealing

Answer 33

seat

Question 34

component of control valve that is housing for the valve internals

Answer 34

body

Question 35

determines how a control valve behaves when it loses its control signal or power

Answer 35

fail-safe design

Question 36

fail-safe design is typically due to:

Answer 36

* Air supply failure * Electric power outage * Instrumentation failure

Question 37

what does the fail-safe positioning ensure

Answer 37

that the valve moves to a predefined "safe" position to protect equipment, the process, or personnel.

Question 38

* Valve opens when air pressure is applied. * Valve closes when air supply fails (spring forces it shut).

Answer 38

air-to-open (fail-closed)

Question 39

* Valve closes when air pressure is applied. * Valve opens when air supply fails (spring forces it open)

Answer 39

air-to-close (fail-open)

Question 40

applications of air-to-open:

Answer 40

* Steam lines – Prevents overheating or over-pressurization. * Fuel or gas feeds – Prevents leaks or combustion in case of failure. * Hazardous chemical feed – Stops chemical flow if control is lost.

Question 41

air-to-close applications

Answer 41

* Cooling water systems – Ensures continuous cooling during emergencies. * Safety relief vents – Allows pressure or gas release when control is lost. * Fire suppression water lines – Keeps water flowing even if air/power is lost.

Question 42

refers to the internal components of a control valve that directly affect the flow of the process fluid

Answer 42

valve trim

Question 43

valve trim includes

Answer 43

* The plug or disk * The seat * The stem * Other flow-modulating components

Question 44

Trim types define the

Answer 44

inherent flow characteristic

Question 45

the relationship between valve stem position and flow under constant pressure drop.

Answer 45

inherent flow characteristic

Question 46

type of valve trim characteristics

Answer 46

linear trim equal percentage trim quick opening trim

Question 47

type of valve trim characteristic where Flow increases exponentially with valve opening

Answer 47

equal percentage trim

Question 48

type of valve trim characteristic where Flow is directly proportional to valve opening (stem position)

Answer 48

linear trim

Question 49

type of valve trim characteristic where flow increases very rapidly with a small change in opening.

Answer 49

quick opening trim

Question 50

type of valve trim characteristics best for systems with constant pressure drop

Answer 50

linear trim

Question 51

advantages of equal percentage trim

Answer 51

Advantages: * More linear installed characteristics in systems with variable pressure drop. * Widely used in chemical and thermal systems

Question 52

type of valve trim characteristic designed for on/off control, not throttling

Answer 52

quick opening trim

Question 53

trim's flow response at constant ΔP

Answer 53

inherent characteristics

Question 54

Actual flow response in the process, influenced by system pressure drops and interaction with pumps, piping, and tanks.

Answer 54

installed characteristic

Question 55

mechanical nonlinearities: * Stem doesn't return to the same position for the same input. * Caused by mechanical play (backlash), actuator lag, or worn parts.

Answer 55

hysteresis

Question 56

mechanical nonlinearities: * A zone where small changes in signal produce no valve motion. * Common in old or poorly tuned valve systems.

Answer 56

deadband

Question 57

mechanical nonlinearities: * Valve resists initial motion due to static friction, then moves suddenly. * Leads to jerky behavior and control loop oscillations.

Answer 57

stiction

Question 58

causes of nonlinear behavior

Answer 58

1. mechanical nonlinearities 2. flow dynamics and system interaction 3. signal transmission and control effects 4. environmental and process factors

Question 59

The closeness of a measured value to the true (actual) value

Answer 59

accuracy

Question 60

The repeatability or reproducibility of measurements under identical conditions.

Answer 60

precision

Question 61

A consistent deviation of measured values from the true value in one direction.

Answer 61

bias

Question 62

bias is caused by

Answer 62

calibration drift sensor aging improper zero/ span adjustment

Question 63

The smallest increment of change that the sensor or transmitter can detect or display.

Answer 63

resolution

Question 64

The ability of the instrument to return the same output when measuring the same input multiple times under identical conditions.

Answer 64

repeatability

Question 65

Similar to repeatability, but under different conditions such as: o Different operators. o Different days or environments. o Different instruments

Answer 65

reproducibility

Question 66

The ratio of the change in output to the change in input

Answer 66

sensitivity

Question 67

Output corresponding to the lowest measured value

Answer 67

zero

Question 68

Difference between the maximum and minimum measurable values

Answer 68

span

Question 69

is the process of adjusting an instrument to ensure that its output accurately reflects the true value of the measured process variable

Answer 69

Calibration

Question 70

Output increases too slowly or too quickly compared to actual input.

Answer 70

gain error

Question 71

Output is shifted too high or too low across the range.

Answer 71

bias (offset)

Question 72

The min to max of the input variable

Answer 72

range

Question 73

how calibration is performed

Answer 73

1. reference input applied 2. output checked 3. error computed 4. zero and span adjustments made`

Question 74

occur when sensors or transmitters cannot respond quickly enough to changes in the process variable

Answer 74

Dynamic measurement errors

Question 75

______ isolates a temperature sensor from the process fluid. Heat must transfer through the ______ walls, which introduces delay.

Answer 75

thermowell

Question 76

detect process variables such as temperature, pressure, flow, and composition

Answer 76

sensors

Question 77

convert physical sensor outputs into standardized electronic or pneumatic signals

Answer 77

transmitters

Question 78

convert one form of signal into another

Answer 78

transducers

Question 79

include pneumatic, analog electronic, and digital

Answer 79

signal types

Question 80

The most common final element in chemical processing

Answer 80

control valves