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Test 2 Flashcards

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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
What can reduce reduce the required length in a pipe before an orifice plate?
Straightening vane
26
Advantages of orifice plates:
- Ease of installation - Easily reproduced - Cheap - Used with a wide range of pipe sizes
27
Disadvantages of orifice plates:
- Erosion/corrosion can change characteristic - High pressure loss - Can clog
28
What is the change in capacitance proportional to?
Change in pressure
29
What does a potentiometric transducer do?
- 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
30
Span of potentiometric transducer?
5-10psi
31
Advantages of a potentiometric transducer
- Small - Cheap
32
Disadvantage of potentiometric transducer
Prone to wear/short lifespan
33
Principle operation of resonance?
Cause a wire to vibrate at its resonant
34
Resonance: since mass and length of a wire is constant...
Any change in frequency will be proportional to wire tension -> which is proportional to applied pressure
35
The resonant frequency of a vibrating wire is a function of...
- The length - The mass - The square root of the tension
36
What is the principle of operation for a piezoelectric transducer?
A crystal compressed under pressure produces voltage and resistance
37
Piezoelectric transducer: tension and compression produce...
opposite voltage polarities
38
LVDT stands for...
linear variable differential transformee
39
LVDT principle of operation:
- 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
LVDT ranges:
0-30psi, 0-10 000psi
41
Disadvantage of LVDT:
Mechanical ware/vibration sensitive
42
Magnetic inductive element principle of operation:
- 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
Magnetic reluctive element principle of operation:
- Magnetic vein attached to bourdon tube changes the gap of magnetic flux path of two iron cores - Reluctance varies with size of gap
44
Optical element principle of operation:
- Movement of pressure element operates optical sensor - As diaphragm moves upwards, vein is lifted,
45
Common ranges of DPT?
-> -3-3"H2O -> -2000-2000psig
46
When measuring a liquid that does not require a liquid seal...
leg elevations (location of transmitter) are below
47
When measuring steam/gas flow that requires a liquid seal...
- the transmitter must be mounted below - filling t's must be at same height
48
When measuring steam/gas flow that does not requires a liquid seal...
- the transmitter must be mounted above - so condensation will fall into pipe
49
Three valve manifold: to isolate or take the transmitter out of service...
- close high side - open equalizer - close low side - Bleed caulk to get rid of pressure
50
Three valve manifold: to put back in service...
- open equalizer - open low-side - close equalizer - open high-side
51
When should all valves in a three valve manifold be open?
Never
52
Five valve manifold: to take out of service...
- close high side - open high equalizer - open low equalizer - close low side - open vent
53
Five valve manifold: to put into service...
- close vent - open low side - close both equalizers - open high side
54
What must a controller incorporate?
A to D (analog to digital) converter
55
What is a smart transmitter?
- All internal components are digital - Output is analog - Can achieve 0.1% accuracy
56
What does a smart transmitter become capable of when part of a dcs (distributed control system)
Being controlled remotely
57
Smart transmitter: Digital "0" represented by...
2200Hz
58
Smart transmitter: Digital "1" represented by...
1200Hz
59
Digital transmitters eliminate the need for...
A/D, D/A converters
60
Digital transmitters eliminate error produced by...
Not reconverting digital signal back to analog
61
The most common wireless technologies use...
radio waves
62
What is a pressure relief valve (PRV)?
- Valve used to control/limit amount of pressure in a system/vessel built up by: - process upset, instrument/equipment failure
63
How does a pressure relief valve relieve pressure?
- Allowing pressurized fluid to flow from auxiliary passage
64
Rupture disk advantages over PRV:
- Cost - Leak tightness
65
Rupture disk disadvantages over PRV:
- one time use - can't be adjusted
66
When is a rupture pin used?
- When a non-resetting PRD is required as a substitute for a rupture disk
67
How does a rupture pin offer savings?
- 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
DP flow meter advantages:
- Familiar/versatile - Lack of moving parts - Suitable for all flow rates in wide variety of pipes/tubes
69
DP flow meter disadvantages:
- Large amount of elements - Square root relationship
70
1 psi to "H20
27.7
71
1 atm to bar
1.01325
72
1 bar to psi
14.5
73
1 atm to psi
14.7
74
1 psi to kPa
6.895
75
1 psi to "Hg
2.04
76
1 inch to mm
25.4
77
As strain gauge is distorted...
- The length of of wire is increased and cross sectional area decreases - both jncreasing resistance
78
A Wheatstone bridge is used...
In strain gauges
79
1 kg/cm^2 to psi
14.22

Measuring (4 decks)

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