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Measuring > Test 2 > Flashcards

Test 2 Flashcards

1
Q

What is a strain gauge

A

Transducer that measures deformation/strain thanks to force

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2
Q

When does strain gauge wire resistance rise?

A

When stretched

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3
Q

What is Epoxy?

A

Specific insulating bendable material

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4
Q

What makes strain gauges useful?

A

Detects very small movements, good for very small pressures

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5
Q

What is change in resistance usually measured with?

A

Wheatstone bridge

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6
Q

What principle does a capacitance pressure element work on?

A

Variable capacitance

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7
Q

What three things alter the value of a capacitor?

A

Size of plates, distance between plates, dielectric material

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8
Q

What does increasing pressure on a capacitor sensor do?

A

Pushes plates together -> changes capacitance -> changes output

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9
Q

What is a capacitance pressure transducer?

A

Diaphragm pressure sensor with a capacitor as the electrical element

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10
Q

What are the five communication protocols?

A

ARCNET, WORLDFIP, HART, Foundation FieldbusH1, Profinet (Profibus)

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11
Q

How do we differentiate between smart and digital transmitters?

A

Smart has both digital and analog outputs, digital only has digital output

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12
Q

What are the 4 types of orifice plates?

A

Concentric, eccentric, segmental, conditioning

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13
Q

What does stamping on one side of an orifice mean?

A

High/sharp side

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14
Q

What are the 5 types of taps?

A

Corner, Flange, Vena Contracta, Pipe, and Radius

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15
Q

Where are corner taps placed?

A

Right up against the orifice plate, where a 90 degree angle would form

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16
Q

Where are flange taps placed?

A

Holes are simply drilled into the flange

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17
Q

Where are Vena Contracta taps located?

A

Upstream: 1D
Downstream: Point of minimum pressure
- Point in fluid system where diameter of stream is least -> fluid velocity is at maximum

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18
Q

Where are radius taps placed?

A

Upstream: 1D
Downstream: D/2

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19
Q

Where are pipe taps placed?

A

Upstream: 2 1/2 D
Downstream: 8D

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20
Q

What do flow elements do?

A
  • Create a differential pressure
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21
Q

Advantages of dp flow meters:

A
  • Familiar/Versatile
  • Lack of moving parts
  • Suitable for all flow rates in a wide variety of pipes and tube
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22
Q

Disadvantages of dp flow meters:

A
  • Many elements required for measurement
  • Square root relationship limits rangeability
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23
Q

What must be used when measuring flow?

A

Square root extractor

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24
Q

What are orifice plates usually made of?

A

High grade stainless steel

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25
Q

What can reduce reduce the required length in a pipe before an orifice plate?

A

Straightening vane

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26
Q

Advantages of orifice plates:

A
  • Ease of installation
  • Easily reproduced
  • Cheap
  • Used with a wide range of pipe sizes
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27
Q

Disadvantages of orifice plates:

A
  • Erosion/corrosion can change characteristic
  • High pressure loss
  • Can clog
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28
Q

What is the change in capacitance proportional to?

A

Change in pressure

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29
Q

What does a potentiometric transducer do?

A
  • Provides a simple method for obtaining an electric output from a mechanical pressure element
  • Uses bourdon/bellows elements
  • Procese pressure moves the wiper over precision potentiometer
  • pressure converts to electrical resistance
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30
Q

Span of potentiometric transducer?

A

5-10psi

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31
Q

Advantages of a potentiometric transducer

A
  • Small
  • Cheap
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32
Q

Disadvantage of potentiometric transducer

A

Prone to wear/short lifespan

33
Q

Principle operation of resonance?

A

Cause a wire to vibrate at its resonant

34
Q

Resonance: since mass and length of a wire is constant…

A

Any change in frequency will be proportional to wire tension -> which is proportional to applied pressure

35
Q

The resonant frequency of a vibrating wire is a function of…

A
  • The length
  • The mass
  • The square root of the tension
36
Q

What is the principle of operation for a piezoelectric transducer?

A

A crystal compressed under pressure produces voltage and resistance

37
Q

Piezoelectric transducer: tension and compression produce…

A

opposite voltage polarities

38
Q

LVDT stands for…

A

linear variable differential transformee

39
Q

LVDT principle of operation:

A
  • Three coils around insulating tube with iron core
  • Alternating current applied to primary coil in center
  • If iron core is centered, equal voltages induced
  • If iron core moves left/right, voltage is induced in other two coils
40
Q

LVDT ranges:

A

0-30psi, 0-10 000psi

41
Q

Disadvantage of LVDT:

A

Mechanical ware/vibration sensitive

42
Q

Magnetic inductive element principle of operation:

A
  • Process pressure moves iron core inside coil
  • Self inductance altered
  • As core is pushed inside coil, inductance is increased proportionally to metal in coil
43
Q

Magnetic reluctive element principle of operation:

A
  • Magnetic vein attached to bourdon tube changes the gap of magnetic flux path of two iron cores
  • Reluctance varies with size of gap
44
Q

Optical element principle of operation:

A
  • Movement of pressure element operates optical sensor
  • As diaphragm moves upwards, vein is lifted,
45
Q

Common ranges of DPT?

A

-> -3-3”H2O
-> -2000-2000psig

46
Q

When measuring a liquid that does not require a liquid seal…

A

leg elevations (location of transmitter) are below

47
Q

When measuring steam/gas flow that requires a liquid seal…

A
  • the transmitter must be mounted below
  • filling t’s must be at same height
48
Q

When measuring steam/gas flow that does not requires a liquid seal…

A
  • the transmitter must be mounted above
  • so condensation will fall into pipe
49
Q

Three valve manifold: to isolate or take the transmitter out of service…

A
  • close high side
  • open equalizer
  • close low side
  • Bleed caulk to get rid of pressure
50
Q

Three valve manifold: to put back in service…

A
  • open equalizer
  • open low-side
  • close equalizer
  • open high-side
51
Q

When should all valves in a three valve manifold be open?

A

Never

52
Q

Five valve manifold: to take out of service…

A
  • close high side
  • open high equalizer
  • open low equalizer
  • close low side
  • open vent
53
Q

Five valve manifold: to put into service…

A
  • close vent
  • open low side
  • close both equalizers
  • open high side
54
Q

What must a controller incorporate?

A

A to D (analog to digital) converter

55
Q

What is a smart transmitter?

A
  • All internal components are digital
  • Output is analog
  • Can achieve 0.1% accuracy
56
Q

What does a smart transmitter become capable of when part of a dcs (distributed control system)

A

Being controlled remotely

57
Q

Smart transmitter: Digital “0” represented by…

A

2200Hz

58
Q

Smart transmitter: Digital “1” represented by…

A

1200Hz

59
Q

Digital transmitters eliminate the need for…

A

A/D, D/A converters

60
Q

Digital transmitters eliminate error produced by…

A

Not reconverting digital signal back to analog

61
Q

The most common wireless technologies use…

A

radio waves

62
Q

What is a pressure relief valve (PRV)?

A
  • Valve used to control/limit amount of pressure in a system/vessel built up by:
  • process upset, instrument/equipment failure
63
Q

How does a pressure relief valve relieve pressure?

A
  • Allowing pressurized fluid to flow from auxiliary passage
64
Q

Rupture disk advantages over PRV:

A
  • Cost
  • Leak tightness
65
Q

Rupture disk disadvantages over PRV:

A
  • one time use
  • can’t be adjusted
66
Q

When is a rupture pin used?

A
  • When a non-resetting PRD is required as a substitute for a rupture disk
67
Q

How does a rupture pin offer savings?

A
  • Eliminates premature failures
  • Prevents need to break integrity of system to institute reset
  • Can be reset without having to remove PRD from system
  • Avoids environmental exposure concerns
  • Enables quick/easy reset when pin requires changing
68
Q

DP flow meter advantages:

A
  • Familiar/versatile
  • Lack of moving parts
  • Suitable for all flow rates in wide variety of pipes/tubes
69
Q

DP flow meter disadvantages:

A
  • Large amount of elements
  • Square root relationship
70
Q

1 psi to “H20

A

27.7

71
Q

1 atm to bar

A

1.01325

72
Q

1 bar to psi

A

14.5

73
Q

1 atm to psi

A

14.7

74
Q

1 psi to kPa

A

6.895

75
Q

1 psi to “Hg

A

2.04

76
Q

1 inch to mm

A

25.4

77
Q

As strain gauge is distorted…

A
  • The length of of wire is increased and cross sectional area decreases
  • both jncreasing resistance
78
Q

A Wheatstone bridge is used…

A

In strain gauges

79
Q

1 kg/cm^2 to psi

A

14.22

Measuring (4 decks)

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