Monitoring and Analysis

Question 1

True or false: Excessive vibration is a symptom of a machine that can lead to machine damage or failure.

Answer 1

True

All machines have some vibration during operation.

Question 2

What is vibration analysis?

Answer 2

Measuring and determining if vibrations are within normal parameters.

Question 3

True or false: Vibration monitoring can be both periodic sampling or constant monitoring.

Answer 3

True

This depends on the type of machinery in use.

Question 4

What is the main limitation of a preventative maintenance program (changing oil at scheduled internals) vs. an oil condition monitoring program?

Answer 4

The levels of oil contamination.

Preventative maintenance oil programs are based off of the expected lifespan of the oil and additives off of running conditions, and are unable to detect excessive contamination.

Question 5

True or false: Over time, lubricating oils lose their ability to separate metal surfaces.

Answer 5

True

Question 6

As it pertains to maintenance, what is infrared thermography (IRT)?

Answer 6

A temeprature analysis programs.

Question 7

True or false: An infrared thermometer is a contact radiant energy detector.

Answer 7

False

It is a noncontact radiant energy detector.

Question 8

____ is the movement of a body about its reference position.

Answer 8

Vibration

Question 9

For rotating equipment, what is the reference point used for vibration analyisis?

Answer 9

The shaft centreline.

Question 10

This test is the only way to find the direct cause of vibration on a machine.

Answer 10

A vibration signature analysis.

A signature is a graphical depiction of vibration frequency.

Question 11

As it pertains to vibration analysis, what is a signature?

Answer 11

A graphical representation of vibration frequency.

Question 12

True or false: With a proper vibration analysis, all vibration in a machine can be eliminated.

Answer 12

False

There will always be some vibration in a machine.

Question 13

All objects vibrate in response to a:

Answer 13

Forcing function

The forcing functions and their signatures indicate the cause of vibration.

Question 14

As it pertains to vibration, what is a forcing function?

Answer 14

An input or influence that causes a system to vibrate.

These can be internal (unbalanced rotor) or external (wind).

Question 15

In machinery, vibration is the accumulation of what three things?

Answer 15

1. the application
2. wear of the machinery
3. machine design

Question 16

What two physical properties of a machine have a direct effect on the vibratory signature of the machine?

Answer 16

1. stiffness
2. mass

Changing either of these will result in a change in the vibratory signature.

Question 17

In vibration analysis, what are sine waves?

Answer 17

Graphical depictions of a vibration cycle.

Question 18

True or false: With vibration, one cycle per minute (cpm) = 1 hertz (Hz).

Answer 18

False

1 cycle per second (cps) = 1 hertz (Hz)

Question 19

How many hertz (Hz) does a vibration signature of 60 cpm equal?

Answer 19

60 cpm = 1 Hz

Hertz is how many cycles per second → 1 cps = 1 Hz = 60 cpm.

Question 20

True or false: With vibration, 1 cps = 1 Hz.

Answer 20

True

1 cps = 1 Hz = 60 cpm

Question 21

With vibration, ____ is how often an event happens in a unit of time or in one cycle.

Answer 21

frequency

Question 22

What are three ways that the frequency of a vibration can be expressed?

Answer 22

1. cycles per second (cps)
2. cycles per minute (cpm)
3. orders*

*Orders are multiples of the operating speed of the machine ⟶ 1x is the same as the rpm, 2x is twice the rpm, etc.

Question 23

When completing vibration analysis on rotating machinery, vibration cycles (frequency) are referenced to what?

Answer 23

The rpm of the machine.

This is the fundamental frequency → Do not confuse cpm with rpm.

Question 24

When it comes to vibration analysis, what are orders?

Answer 24

Multiples of the operating speed of the machine.

2x order → 2x machine rpm = twice per revolution.

Question 25

With vibration analysis, what is the frequency with the highest (loudest) spike called?

Answer 25

The predominant frequency

This is the lowest or first frequency normally associated with a problem

Question 26

On vibration analysis, what is the fundamental frequency?

Answer 26

The frequency that corresponds to the machine rpm.

This can also be the most prominent frequency with the highest spike.

Question 27

With vibration analysis, what is amplitude?

Answer 27

How much the machine is vibrating.

How “loud” the vibration is.

This is the distance from the at rest position and indicates the magnitude of the vibration.

Question 28

What are three ways that the amplitude of a vibration are measured?

Answer 28

1. displacement
2. velocity
3. acceleration

These are the three parameters used to describe the amplitude of a vibration, and are selected based off of the frequency of the vibration.

Question 29

This type of vibration amplitude measurement is the total distance a vibrating part moves either side of its neutral axis.

Answer 29

Displacement

On a displacement sine wave, this measurement is peak to peak.

Question 30

With vibration analysis, how is the total displacement (peak to peak) measurement measured in:
1. Imperial
2. Metric

Answer 30

1. Imperial → mils pk to pk
2. Metric → microns pk to pk

pk = peak

Question 31

This vibration amplitude measurement is the peak to peak measurement of the sine waveform.

Answer 31

Displacement

This is measured in mils pk to pk and microns pk to pk.

Question 32

When completing a vibration analysis, what type of amplitude measurement parameter would be used for below 600 cpm or 1000 rpm?

Answer 32

Displacement

This is often used where stress conditions such as flexing and bending are suspected and in balancing procedures.

Question 33

This type of vibration amplitude measurement is often used where stress conditions such as flexing and bending are suspected and in balancing procedures.

Answer 33

Displacement

This is best used on equipment and vibrations below 600 cpm or 1000 rpm.

Question 34

This type of vibration amplitude measurement is the rate of change of displacement for a given time.

Answer 34

Velocity

Velocity combines displacement (how far it moves) and frequency (how often).

Question 35

With vibration analysis, when placed on a sine wave, when does maximum velocity take place?

Answer 35

At the neutral axis

The velocity of a part changes from zero at one extreme of the motion to a maximum velocity in the middle (as it crosses the zero axis) and then back to zero velocity at the other extreme of the movement.

Question 36

When using velocity to measure the amplitude of a vibration, what velocity measurement is used?

Answer 36

Maximum velocity

This is the measurement of velocity as it passes the zero axis.

Question 37

With vibration analysis, velocity is measured in what units in:
1. Imperial
2. Metric

Answer 37

1. Imperial → in/sec or ips*
2. Metric → mm/sec

*ips = inches per second

Question 38

When completing a vibration analyisis, what type of amplitude measurement parameter would be used between 600 cpm and 60,000 cpm?

Answer 38

Velocity measurements

Question 39

1. Which vibration amplitude measurement parameter is the best indicator of overall machine condition?
2. Why is this?

Answer 39

1. Velocity measurements
2. It provides a balance between sensitivity to small vibrations and the ability to detect larger issues

Velocity is proportional to the energy transmitted by vibration, which correlates well with the potential for mechanical damage or wear. This makes velocity readings a good indicator of how “destructive” the vibration is to the machine.

Question 40

Which vibration amplitude measurement parameter works over the widest range of frequencies?

Answer 40

Velocity

From 600 cpm to 60,000 cpm

Question 41

This type of vibration amplitude parameter is the rate of change in velocity.

Answer 41

Acceleration

Acceleration is measured in g’s force.

Question 42

What type of vibration amplitude is measured in g’s force?

Answer 42

Acceleration

Question 43

When measuring amplitude with acceleration, where does maximum acceleration occur on a sine wave?

Answer 43

At the top and bottom of the waveform.

Maximum acceleration occurs twice during one time period.

The greatest acceleration occurs when the object begins to move from zero velocity at the extremes of travel ⟶ this is the area of the greatest rate of change in velocity.

Question 44

With acceleration amplitude measurements, where does the least amount of acceleration happen?

Answer 44

At the zero axis.

This coincides with the greatest velocity ⟶ velocity ↑ = acceleration ↓

Question 45

When completing a vibration analyisis, what type of amplitude measurement would be used on frequencies over 60,000 cpm?

Answer 45

Acceleration

This is because at high frequencies displacement and velocity measurements don’t accurately indicate how severe the vibration is.

Question 46

1. On vibration analysis, what is phase?
2. What is phase used for on a vibration analysis?

Answer 46

1. A time relationship between two points measured in degrees.
2. To indicate the relative position of a vibration and a reference point (either a fixed location or another vibration).

Phase is measured or expressed in degrees.

Question 47

On a vibration analysis, what is an in-phase vibration?

Answer 47

A vibration where both pick-up spots are moving in the same direction and at the same time.

Question 48

On a vibration analysis, what is an out of phase vibration?

Answer 48

A vibration where both pick-up spots are not moving in the same direction or at the same time.

The phase difference is measured in degrees.

Question 49

When taking a vibration phase reading, keep the accelerometers facing the same direction. What needs to be done if this is not possible?

Answer 49

Change the reading of one accelerometer by the corresponding degree angle.

This ensures that the accelerometers read the proper phase angle on the vibrations.

Question 50

When measuring vibration, what determines which parameter is selected for amplitude measurement?

Answer 50

The frequency

Depending on the frequency, either displacement, velocity, or acceleration would be selected.

Question 51

This vibration frequency is the frequency at which an object or system naturally vibrates when a forcing function has been introduced.

Answer 51

Natural frequency

Factors that affect the natural frequency of an object are size, material, length, and shape.

Question 52

In the case of shafts, the natural frequency is ____ (lower/higher) depending on the stiffness of the shaft.

Answer 52

higher

Stiffer = higher frequency

Question 53

This type of frequency is where the system or machine amplifies the energy from the forcing function, causing a large amplitude (greater vibration).

Answer 53

A resonant frequency

Resonant frequencies destroy machines.

Question 54

Resonance occurs in any system if the forcing function frequencies are not kept at least ____% outside the natural frequency’s range.

Answer 54

20%

If not, the forcing function aligns with the natural frequency of the system, resulting in the energy of the forcing function amplifying the natural frequency.

Question 55

In vibration analysis, a ____ is the time required to complete on cycle of a periodic signal.

Answer 55

period

Question 56

What is the critical speed of a machine?

Answer 56

The speed of a shaft or rotor when it is near its natural frequency and begins to resonate.

Question 57

What happens to a rotor or shaft at critical speed?

Answer 57

It begins to resonate.

This increases vibration drastically, resulting in failure.

Question 58

Machines should not be operated at or near the critical speed of the shaft or rotor, and should be kept ____% outside of a rotor’s critical speed.

Answer 58

20% to 30%

Question 59

In vibration analysis, what is a harmonic?

Answer 59

A multiple or sub-multiple of the fundamental frequency.

The fundamental frequency is the rpm of the machine.

Question 60

True or false: You must know the running speed of a machine or shaft rpm in order to properly diagnose a vibration issue.

Answer 60

True

This becomes your baseline or fundamental frequency.

Question 61

As it pertains to vibration analysis, what is a synchronous vibration?

Answer 61

A vibration frequency that is a whole multiple of the fundamental frequency (rotating speed) of the machine.

These are phase locked to the rpm of the machine, such as 1x rpm, 2x rpm

Question 62

As it pertains to vibration analysis, what is a non-synchronous vibration?

Answer 62

Vibration frequencies that are not whole multiples of the rotating speed of the machine.

Question 63

As it pertains to vibration analysis, what is a sub-synchronous vibration?

Answer 63

Vibration frequencies that occur at less than the rotating speed (fundamental frequency) of the machine.

Question 64

True or false: When using ISO vibration severity charts, when using velocity to determine the level of vibration, you ignore frequency.

Answer 64

True

In this example, the velocity is 0.200 in/sec.

Velocity is the only parameter that is selected without having to meet two points together on the severity chart.

Question 65

True or false: When using ISO vibration severity charts with displacement to determine the level of vibration, you use both the frequency and the peak to peak measurement, and where these two lines instersect indicates the severity of the vibration.

Answer 65

True

In this example the displacement was 0.20 mils pk to pk at 1200 cpm.

Question 66

True or false: When using ISO vibration severity charts with acceleration to determine the level of vibration, you use both the frequency and the peak g’s measurement, and where these two lines instersect indicates the severity of the vibration.

Answer 66

True

In this example, the acceleration was 0.26 g’s at 30,000 cpm.

Question 67

With vibration analysis, this type of processor capability allows it to change the signal received from the transducer from amplitude vs. time to amplitude vs. frequency, allowing it to create a signature by adding up the sine waves at each frequency and stacking them up in order of the frequency.

Answer 67

A fast fourier transformer (FFT) processor

This converts a sine wave (time vs. amplitude) into a vibration signature (frequency vs. amplitude).

Question 68

This type of vibration measurment tool is used for precautionary measurements and to establish quick measurements of a specific vibration characteristic.

Answer 68

Vibration pencils/pens

This diagnostic tool measures the one amplitude of the frequency ⟶ usually the dominant or fundametal frequency.

Question 69

True or false: Portable vibration meters are capable of taking overall vibration readings, and if equipped with a FFT, break down the vibration into a series of discrete frequencies and amplitudes.

Answer 69

True

Question 70

Vibration ____ are meters that are permanently installed in a plant to continually check the vibrations of a certain piece of equipment.

Answer 70

monitors

These are used on equipment that must maintain a high degree of quality control, with some monitors being capable of shutting down the machine if excessive vibration is detected.

Question 71

Which type of vibration measuring device is capable of separating individual frequencies, making problems easier to identify.

Answer 71

Vibration analyzers

Question 72

Vibration ____ are more complex and expensive than meters and monitors, and are capable of measuring vibrations by all of their characteristics.

Answer 72

analyzers

These are capable of separating individual frequencies, making problems easier to identify.

Question 73

What is the most important component of a vibration measurement system?

Answer 73

The transducers

This are responsible for providing accurate information to the analyzer.

Question 74

What are the three basic types of vibration transducers?

Answer 74

1. Displacement transducers
2. Velocity transducers
3. Acceleration transducers (accelerometers)

A transducer is a device that converts mechaincal motion of a vibration into an electrical signal which is then translated into a numerical value.

Question 75

This type of vibration measurement uses proximity probe transducers to measure the relative distance between a bearing housing and a bearing journal.

Answer 75

Displacement transducers

These are non-contact eddy current proximity probes.

Question 76

This type of vibration transducer works by generating a magnetic field that induces eddy currents in the conductive surface. Changes in distance alter the eddy currents, which are converted into an electrical signal proportional to the vibration.

Answer 76

Displacement proximity probes

The change or loss in voltage is proportional to the distance between the probe and its target.

Question 77

What type of material does the shaft need to be made out of in order for an eddy current vibration probe to work?

Answer 77

Metal

It must be made of a conductive material.

Question 78

Which type of vibration transducer requires an external power supply?

Answer 78

Displacement (eddy current) transducers

A power supply is required to create a small magnetic field near the shaft.

Question 79

What are two conditions that adversely affect the proximity probes used to measure displacement vibrations?

Answer 79

1. shaft run-out
2. scrates or variations on the shaft surface

Question 80

This type of vibration transducer is used for general vibration measurements and balancing.

Answer 80

Velocity transducers

These are physically the largest types of vibration transducers.

Question 81

This type of vibration transducer is made of a coil of wire that is fixed in the case, with a permanent magnet moving within the coil. When held against a vibrating object, the magnet moves back and forth relative to the coil, inducing a voltage.

Answer 81

A velocity transducer

The faster the motion of the vibration, the larger the voltage ⟶ the voltage is proportional to the velocity of the motion.

Question 82

True or false: Velocity vibration transducers require an external power supply.

Answer 82

False

Velocity transducers generate their own internal power through the relative motion between a coil and a permanent magent.

Question 83

True or false: While primarily used to measure velocity, velocity transducers are capable of measuring displacement and acceleration.

Answer 83

True

They are not very reliable when measuring low frequencies for displacement or very accurate when measuring the high frequencies for acceleration.

Question 84

What are the most common types of vibration transducers used in industry?

Answer 84

Acceleration transducers (accelerometers)

Question 85

This type of vibration transducer uses piezoelectric materials as the sensing component, which produces a small voltage proportional to the amount the material is strained or compressed.

Answer 85

Acceleration transducers

The two common types of piezoelectric materials are quartz and ceramics.

Question 86

Of the two types of piezoelectric materials listed in the module, which one is better for high temepratures?

Answer 86

Ceramics

Quartz is more stable, but the ceramics can handle higher temperatures.

Question 87

True or false: Accelerometers are affected by magnetic fields.

Answer 87

False

Piezoelectric materials are not affected by magnetic fields.

Question 88

What are the two types of excitation methods for the piezoelectric materials found in accelerometers?

Answer 88

1. Compressive mode
2. Shear mode

Both methods produce a voltage that is porportional to the amount of compression.

Question 89

Which type of vibration transducer is especially sensitive to vibration occuring at very high frequencies?

Answer 89

Accelerometers

These are best suited for vibrations over 60,000 cpm.

Question 90

With which type of vibration transducer is proper mountin critical?

Answer 90

Acceleration transducers

Mounting for all types of vibration transducers is important.

Question 91

What type of vibration transducer would be used to measure the vibrations of larger turbo machinery?

Answer 91

Displacement transducers

Question 92

Which type of vibration transducer can be used to measure all of the vibration frequency parameters?

Answer 92

Accelerometers

Question 93

What issues arise if vibration transducers are not properly mounted?

Answer 93

Inaccurate readings

Poor mounting can amplify or distort the readings

The transducer and the mounting arrangement is the most important component of the vibration system → poor data fucks everything up.

Question 94

What are the five methods of mounting vibration transducers and identify which one is the best, good, and fair.

Answer 94

1. Stud mount → best
2. Magentic pick-up mount → good
3. Hand-held probe → fair
4. Adhesive bond to surface
5. Shaft rider assembly

Ensure that the transducer is mounted the same way each time measurements are taken, as this could introduce another variable into the data.

Question 95

When mounting vibration transducers, why is silicone grease applied to any two flat mating surfaces?

Answer 95

Improved surface contact

This reduces signal loss between flat surfaces.

Surfaces, even very smooth ones, have irregularities on them. The silicone grease fills these, improving the transfer of vibrations between surfaces.

Question 96

This vibration transducer accessory is used to continuously and accurately monitor the absolute shaft vibration of a machine through a long-wearing, non-metallic tip installed near the bearing area.

Answer 96

Shaft rider accessory

The contact tip needs to be lubricated.

These accessories are used to continuously monitor vibration.

Question 97

True or false: Vibration transducers are only able to pick up vibrations that are in line with the transducer.

Answer 97

True

This makes the direction or position important when measuring vibration.

Question 98

As it pertains to vibration analyisis, what are HVA positions?

Answer 98

Horizontal, Vertical, and Axial positions

These are the ideal transducer locations on each bearing, resulting in the most complete vibration picture.

Question 99

On rotating equipment, where should vibration tranducers be mounted?

Answer 99

As close as possible to the bearing locations and on solid surfaces only.

Ideally in HVA positions (if possible).

Vibrations in flexible surfaces may be amplified by the resonant frequency of the surface, resulting in inaccuracte readings.

Question 100

What are the two main fuctions of a strobe light when being used for vibration analysis?

Answer 100

1. Freeze motion to observe rotating components
2. Measure the phase angle when balancing parts

These are also known as stroboscopes.

Question 101

When using a strobe light during a vibration analysis, what four issues could be identified by using the strobe light to freeze motion to observe the rotating components of the machine?

Answer 101

1. Misalignment ⟶ components that appear offset or wobble
2. Imbalance ⟶ asymmetrical rotation of rotors or fans
3. Bent shafts ⟶ A “wobbling” or elliptical motion of the shaft rather than smooth circular rotation
4. Loose parts or couplings ⟶ loose bolts, couplings, or other parts visibly shifting during rotation

Question 102

True or false: Strobe lights can be adjusted manually so that it can be used as a tachometer or so you can study the slow motion response of machine parts.

Answer 102

True

Question 103

With vibration analysis, stobe lights can be set to be triggered by vibration transducers at the same speed as the dominant frequency. What are two things that this helps to identify?

Answer 103

1. Identify which components are producing the vibration signal.
2. Determine the relationship (phase) of the components that are excited by the vibration.

This helps to identify the phase angle between the transducer and the predominant vibration.

Question 104

What are the two overall steps used in vibration analysis procedures?

Answer 104

1. Data aquisition
2. Data interpretation

Question 105

With vibration analysis, what four steps make up the data aquisition phase?

Answer 105

1. Identify the nature of the problem
2. Gather information about the vibrating system
3. Make a sketch of the machine, with support data
4. Take vibration readings

Question 106

With vibration analysis, what two steps make up the data interpretation phase?

Answer 106

1. Analyze vibration data
2. Make corrective recommendations

Question 107

True or false: the more complete the initial vibration analysis investigation, the more accurate the conclusion reached.

Answer 107

True

Question 108

Why is it imporant to check for vibration after the machine has stopped?

Answer 108

Significant backround vibrations can make the origional readings inaccurate

If certain vibrations persist after the machine has been shut down, the vibration model will have to be adjusted in order to get an accurate picture.

Question 109

True or false: noise and vibration are the same thing.

Answer 109

False

Noise can be associated with vibration, but they are not the same thing.

Question 110

When dealing with vibration and noise issues, 1.________ solves noise issues, while vibration is solved by 2.________.

Answer 110

1. isolation and insulation
2. correcting the root problem

Question 111

With vibration analysis, ____ is a disturbance caused by a sudden applied force.

Answer 111

shock

Shock vibratons die out before the next impulse vs. vibration which is a continuous condition.

Question 112

True or false: Noise and shock issues can be identified with vibration analysis.

Answer 112

False

Vibration analysis is not effective at determining the cause of shock or noise frequencies.

Question 113

What can cause the amplitude of a harmonic to exceed the amplitude at the force’s frequency?

Answer 113

Resonance within the system

Question 114

True or False: Resonance always decreases the amplitude of harmonics.

Answer 114

False

Question 115

How does a sketch of the machinery aid with vibration analysis (3 things)?

Answer 115

1. Allows you to determine the best data collection points
2. Aids in determining potential sources of vibration
3. Consistency*

The sketch allows you to re-take measurements from the same locations in the future, which ensures consistency in the measurements.

Question 116

In most machines, a vibration has a 1.________ level and its frequency spectrum has a 2.________ shape when the machine is in good condition.

Answer 116

1. typical
2. characteristic

This is the vibration signature of the machine.

Question 117

1. What is the vibration signature of a machine?
2. When should it be first taken?

Answer 117

1. A unique pattern of vibration characteristics generated by a machine during operation
2. When it is first installed ⟶ this provides the baseline

Question 118

In a vibration signature, the loweset frequency is usually the:

Answer 118

fundamental frequency

This is the rpm of the machine.

Question 119

On a vibration signature, what is the largest frequency known as?

Answer 119

The (pre)dominant frequency

This can sometimes be the same as the fundamental frequency.

Question 120

What kind of frequency would an imbalance characteristic have?

Answer 120

1x the machine rpm (fundamental frequency)

Imbalance is always 1x the fundamental frequency.

Question 121

What is the grass on a vibration graph?

Answer 121

The small vibration amplitudes to each side of the dominant frequencies.

These should not be ignored, as they can indicate future issues.

Question 122

What kind of frequency would a misalignement or mechanical looseness show up as?

Answer 122

2x the fundamental frequency

Question 123

What are the two most common causes of vibration in rotating machinery?

Answer 123

1. Imbalance
2. Shaft misalignment

Question 124

On vibration analysis, a rotor or shaft imbalance can be indentified by a vibration frequency ____x rpm.

Answer 124

1x rpm

This would be a 1x order.

Question 125

1. On a vibration analysis, a rotor or shaft imbalance usually has the largest amplitude in what HVA direction?
2. When is the above not the case?

Answer 125

1. The radial (horizontal and vertical) direction
2. With an overhung rotor ⟶ then the largest amplitude is in the axial direction

Question 126

On a vibration analysis, in what HVA direction would the largest amplitude be on an overhung rotor indciating imbalance issues?

Answer 126

In the axial direction

Question 127

With a vibration analysis indicating imbalance, what happens to the amplitude of the vibration as the shaft speed increases?

Answer 127

shaft speed ↑ = amplitude ↑

With imbalance, amplitude increases with the speed of the machine.

Question 128

True or false: On vibration analysis, if imbalance is causing the vibration, the phase of the exciting force changes on each revolution.

Answer 128

False

With imbalance, the phase of the exciting force does not change.

Question 129

With vibration analysis, what kind of phase readings would be expected with imbalance issues?

Answer 129

Stable, following the location on which the transducer is mounted.

This means that the phase angle between the horizontal and vertical measurements is constant when readings are taken on opposite ends of the rotor.

Question 130

True or false: With vibration analysis, the amplitude of an imbalance vibration is proportional to the degree of imbalance.

Answer 130

True

Question 131

With vibration analysis, what kind of frequency order would a slightly misaligned shaft have?

Answer 131

1x order (usually)

A severely misaligned shaft could see orders of 2x or 3x.

Question 132

With vibration analysis, what kind of frequency order would a severely misaligned shaft have?

Answer 132

2x or 3x order

An order is a multiple of the machine rpm ⟶ 2x = twice machine rpm, etc.

Question 133

With a HVA vibration analysis, what type of misalignment causes a high axial vibration component (1/2 or more of the radial amplitude)?

Answer 133

Angular misalignment

Question 134

With a HVA vibration analysis, what type of misalignment causes the radial component (H&V) of the vibration to be high?

Answer 134

Parallel (offset) misalignment

Question 135

True or false: With vibration analysis, the amplitude of a misalignment vibration is proportional to the to the misalignment.

Answer 135

True

The more misaligned the coupling, the greater the vibration.

Question 136

With vibration analysis, an axial vibration of ____% or more of the radial is a good indicator of misalignment.

Answer 136

50% or more

Question 137

With vibration analysis, a misaligned shaft will have what kind of phase angles between the horizontal and vertical measurements?

Answer 137

Erratic, and often different at opposite ends of the rotor

Question 138

This type of vibration signature acts like an imbalance and has radial vibration frequencies at 1x rpm and 2x rpm.

Answer 138

Eccentricity of the electrical field

This example is due to stator (motor) eccentricity.

Question 139

What are the main differences between a vibration signature due to rotor electrical eccentricity vs. one indicating imbalance?

Answer 139

Rotor eccentricity generates a more dominant two times frequency with smaller frequency side bands at both the 1x rpm and 2x rpm

Question 140

What are the two main causes of vibration due to eccentricity of the electrical field?

Answer 140

1. soft foot
2. incorrect/uneven air gap (between the rotor and stator)

Question 141

When troubleshooting a vibration analysis, and eccentricity of the electrical field is suspected, what should happen to the vibration (amplitude and frequency) when power is shut off to the motor?

Answer 141

The vibration amplitude should drop immediately.

If the amplitude “coasts” down in proportion to the rpm of the machine, the vibration is being caused by some other issue → misalignement or imbalance.

Question 142

When performing a vibration analysis, what does component eccentricity act like?

Answer 142

Imbalance

Component eccentricity will have a predominant vibration in the radial direction at 1x fundamental frequency.

Question 143

On vibration analysis, what kind of frequencies would be expected when examining gearboxes?

Answer 143

A multiple of the number of teeth x the rpm

This is called the gear mesh frequency (GMF).

An input shaft rotating at 1000 rpm driving a gear with 8 teeth → 1000 rpm x 8t = 8000 cpm frequency

Question 144

What formula is used to calculate the gear mesh frequency of a gearbox when performing a vibration analysis?

Answer 144

GMF = # teeth on the gear x rotational speed of the gear (in Hz or RPM)

This is an approximate method of finding the vibration frequency.

Question 145

When examining a vibration analysis of a gerabox, the frequency of the vibration should usually be several times higher than 1x rpm (due to rpm x teeth). When is that not the case?

Answer 145

When only one tooth on a gear is bad.

This will show up as a 1x rpm vibration frequency.

Question 146

On a vibration analysis, this type of issue produces a series of sharp, high-frequency impulses that have many sharp edges.

Answer 146

Anti-friction bearing issues

Frequencies for bearing problems in the early stages are very high.

BPFO = ball pass frequency outer race

Question 147

What four things affect the vibration frequencies of defective roller bearings?

Answer 147

1. ball diameter
2. number of balls in the bearing
3. pitch diameter of the path of the balls
4. speed of the shaft

Question 148

What formula is used to calculate the ball pass frequency (in cpm) for a bearings inner race?

Answer 148

BPFI (frequency) = 0.60 x n x rpm

• BPFI → ball pass frequency inner race (in cpm)
• n → # of rolling elements
• rpm → rotational speed of the bearing

This formulas assume a single defect on the bearing.

Question 149

What formula is used to calculate the ball pass frequency (in cpm) for a bearings outer race?

Answer 149

BPFO (frequency) = 0.40 x n x rpm

• BPFO → ball pass frequency outer race (in cpm)
• n → # of rolling elements
• rpm → rotational speed of the bearing

This formula assumes a single defect on the bearing.

Question 150

True or false: When examining a vibration analysis, the vibration frequency of an anti-friction bearing is usually an exact multiple of the shaft rpm.

Answer 150

False

Anti-friction bearing vibration frequencies depend on the ball pass frequency of one or both of the races, and is usually not an exact mulitple of the shaft rpm.

Question 151

True or false: With plain bearings, if the bearing clearances are too loose, the shaft can move around and pount on the bearing, causing a vibration signature.

Answer 151

True

This is also known as eccentric journals

Question 152

____ ____ (2 words) occurs when the shaft in a plain bearing climbs the oil wedge created by the shaft rotation, moving to a different position within the bearing, resembling an orbit.

Answer 152

Oil whirl

This instability of the shaft causes vibration.

Question 153

What type of vibration frequencies are created by oil whirl?

Answer 153

45% to 50% of the fundamental frequency

Question 154

True or false: Plain bearing oil whirl is usually caused by the wrong viscosity oil (or cold oil), excess clearances, or improper lubricaion.

Answer 154

True

Pivoted shoe radial bearings are often used where oil whirl is a chronic problem.

Question 155

When taking a vibration analysis, and bearing damage is suspected, what HVA plane(s) would the vibration amplitude be the greatest?

Answer 155

In the direction of the load

With radial bearings, that would be in the H and V planes, and in the axial plane for thrust bearing issues.

Question 156

This cause of vibration is identified by a dominant vibration at 2x rpm and vibrations at other frequencies such a 1/2x and 4x rpm.

Answer 156

Mechanical looseness

Mechanical looseness refers to loose hold-down bolts on motors, pumps, bearing caps or pillow blocks, etc.

Question 157

When measuring vibration caused by mechanical looseness with an HVA assembly, where would the greatest forces be observed?

Answer 157

In the radial direction

There may be close to no axial movement, depending on the machine.

Question 158

True or false: If adjacent parts on a machine show different amplitude and phase readings, the relative motion between the parts could be the cause of the vibration.

Answer 158

True

If you get different phase readings at any spot, it means that location is moving differently.

Question 159

True or false: Single drive belt arrangements are more susceptible to belt vibrations.

Answer 159

False

Multiple belt drives are more susceptible to belt vibration.

Question 160

True or false: When completing a vibration analysis, belt vibrations usually show up as mutliples of the machine speed (1x, 2x, 3x, or 4x the rpm of the belts).

Answer 160

True

Question 161

With vibration caused by belts, the vibration from the belts is greatest in the direction of:

Answer 161

belt tension

Question 162

With vibration analysis, what issue could cause a vibration signature with 1x and 2x orders, along with different phase readings at opposite ends of the bearing housing?

Answer 162

A bent shaft.

Remember bearing housing.

These may look like a misalignment or imbalance issue, but with very high vibration readings in both the axial and radial directions.

Question 163

Why are blade and vane problems associated with higher orders of the fundamental frequency of the fan?

Answer 163

These frequencies correspond with a multiple of the blades or vanes passing.

The more blades a fan has, the higher these frequencies will be.

Question 164

How is the frequency of vibration typically calculated for fan blades or vanes?

Answer 164

of fan blades x rpm (fundamental frequency) of the shaft

This means that each blade contributes to the overall vibration frequenc

fan frequency = # of blades x rpm ⟶ 6 blades x 1500 rpm = 9000 cpm frenquency

Question 165

What formula can be used to calculate the vibrational frequency that a fan could introduce into a vibration signature?

Answer 165

fan frequency = # of fan blades x fan rpm

This is known as the blade pass frequency of the fan.

Question 166

What happens to the vibration signature if a fan blade is missing or damaged in a system?

Answer 166

An imbalance situation, resulting with a 1x rpm predominant frequency

This can lead to increased vibrations and potential damage.

Question 167

What is rubbing in the context of machinery?

Answer 167

Unwanted friction between two machine parts

This is a common issue in machines like steam turbines and compressors.

Question 168

What types of machines commonly experience rubbing problems?

Answer 168

• Steam turbines
• Centrifugal compressors
• Axial flow compressors
• Other high-speed turbo machinery

These machines are particularly susceptible due to high surface speeds.

Question 169

What causes rubbing in machines?

Answer 169

Deflection of rotors or impellers, wearing of components resulting in smaller gaps, etc.

Anything that results in the spaces between components getting smaller.

Question 170

At what frequencies does rubbing typically vibrate?

Answer 170

• 1x rpm
• 2x rpm
• Higher frequencies
• Less than 1x rpm

Rubbing can generate vibrations at various harmonic frequencies.

Question 171

True or false: Belts are capable of both dampening shock and vibration, while at the same, can also be the cause of vibration.

Answer 171

True

Belt vibration is due to some underlying condition affecting the belts, such as misaligned sleeves, loose belts, etc.

Question 172

What type of motion can belts develop due to disturbing forces?

Answer 172

Bouncing or whipping motion

Question 173

What can cause belts to exhibit a bouncing or whipping motion?

Answer 173

Loose, misaligned belts or eccentric sheaves

Question 174

What can result from radical torque variations in belts?

Answer 174

Stretch and bounce of the belts

Question 175

True or false: Adding or removing weight, standing on a part, or clamping or bracing it can cause changes to occur in a vibrating object.

Answer 175

True

This will change the vibration signature of the object.

Question 176

What is indicated when the vibration of a machine changes due to weight adjustment?

This could be from adding or removing weight, standing on a part, or clamping or bracing it.

Answer 176

The machine is resonating.

This weight changes the natural frequency of the machine, which results in a different critical speed.

Question 177

When a machine is resonating, where does most of the resonance originate from?

Answer 177

From a non-rotating part, usually within the first 3 to 4 metres from the rotating part.

Question 178

What types of machines commonly have resonance issues?

Answer 178

Fans and blowers

Question 179

True or false: The piping is often the source of resonance in systems.

Answer 179

True

To correct for this type of resonance, it is best to “stiffen” the piping assembly by adding additional supports.

Question 180

What occurs when the running speed coincides with the natural frequency of the pipe?

Answer 180

Resonance

This is the critical speed of the machine, and the resulting vibrations can tear the machine apart.

Question 181

What methods can change the natural frequency of a pipe?

Answer 181

Extra braces, supports, or expansion joints.

The idea is to “stiffen” the piping, changing its natural frequency.

Question 182

Fill in the blank: Almost all of resonance originates from a:

Answer 182

non-rotating part

Question 183

What is the frequency of vibration caused by imbalance?

Answer 183

1x rpm

Question 184

What is the phase characteristic of imbalance vibration?

Answer 184

Stable and repeatable

The vibration will happen in the same spot, and at the same phase angle.

Question 185

How does the amplitude of vibration behave for imbalance?

Answer 185

It is proportional to the imbalance

The greater the imbalance, the “louder” the vibration.

Question 186

What frequencies are associated with misalignment?

Answer 186

1x, 2x, or 3x rpm

Question 187

What percentage of axial amplitude is typically seen in misalignment?

Answer 187

50% or larger of radial amplitude

Question 188

How does the phase behave in misalignment vibration?

Answer 188

It can show in 1, 2, or 3 positions

The phase angle between H and V measurements are often different at opposite ends of the rotor.

Question 189

What is the frequency characteristic of vibration caused by anti-friction bearings?

Answer 189

Very high frequency, several times rpm

Look for very high frequency vibrations with sharp pulses.

Question 190

What is the amplitude of vibration for anti-friction bearings?

Answer 190

Not large

Question 191

How is the phase described for anti-friction bearing vibration?

Answer 191

Erratic

Question 192

What should you look for with anti-friction bearing vibration?

Answer 192

Look for very high-frequency vibrations with sharp pulses

Question 193

What is the frequency of vibration caused by eccentric journals?

Answer 193

1x rpm

This often acts like an imbalance, and could be mistaken for one.

Question 194

How is the amplitude of vibration for eccentric journals?

Answer 194

Not large

Question 195

What is the phase characteristic of eccentric journal vibration?

Answer 195

A single phase location

Question 196

How does eccentric journal vibration behave?

Answer 196

Acts like an imbalance

Question 197

What is the frequency of vibration caused by gear problems?

Answer 197

A very high frequency ⟶ gear teeth × rpm

Question 198

What is the amplitude characteristic of gear problems?

Answer 198

Low

Use velocity or acceleration transducers to detect the vibrations.

Question 199

How is the phase described for gear problems?

Answer 199

Erratic

Question 200

What should you use to identify gear problem vibrations?

Answer 200

Use velocity or acceleration at higher frequencies

Question 201

What frequencies are associated with mechanical looseness?

Answer 201

2x rpm or 4x rpm

The dominant vibration is usually the 2x order of the fundamental frequency.

Question 202

How is the amplitude for mechanical looseness described?

Answer 202

Erratic

Question 203

What is the phase characteristic of mechanical looseness?

Answer 203

Two reference marks

Question 204

What is a common observation about mechanical looseness?

Answer 204

It may be accompanied by imbalance or misalignment.

Question 205

What frequencies are associated with drive belt problems?

Answer 205

1x, 2x, 3x, or 4x rpm of the belts

Question 206

How is the amplitude of drive belt problems described?

Answer 206

Erratic pulsing

Question 207

What is the phase characteristic of drive belt problems?

Answer 207

1 or 2, usually unsteady

Question 208

What tool can be used to observe drive belt problems?

Answer 208

A strobe light ⟶ this can freeze the belts.

Question 209

What is the frequency of vibration caused by electrical forces?

Answer 209

1x rpm or 1x or 2x synchronous frequency

Question 210

How does the amplitude behave for electrical forces?

Answer 210

It disappears when power is removed from the machine

Question 211

What is the phase characteristic of electrical forces vibration?

Answer 211

1 or 2 marks

Question 212

What happens to the amplitude of electrical forces vibration when power is turned off?

Answer 212

The amplitude drops off

Question 213

Which reading is used to see how one part is shaking/vibrating in relation to another part?

Answer 213

Phase

Phase angles are expressed in degrees.

Question 214

This cause of vibration creates similar amplitude in both the horizontal and vertical planes.

Answer 214

Imbalance

This type of amplitude reading is usually only found when imbalance is the cause of the vibration.

Question 215

Why can you not ignore the small vibrations showing up at each side of the dominant frequency on the graph?

Answer 215

They could be indications of impending bearing troubles.

Question 216

What two maintanence analysis programs can be used together to form an overall picture of a machine’s condition?

Answer 216

1. Vibration analysis
2. Oil analysis

Question 217

Infrared thermography allows for the measurement of:

Answer 217

heat being emitted

Question 218

For many industries, 1.________ analysis has been the primary technique for monitoring machine health, while 2.________ analysis is the preferred method used in the mobile and heavy equipment industry.

Answer 218

1. vibration
2. oil

Combining the two techniques is an effective way to monitor machine condition.

Question 219

Which type of machine conditioning analysis program would be best to identify component wear from sliding parts?

Answer 219

Oil analysis

Vibration monitoring won’t indicate an issue until the parts have worn to a point where there is excessive clearance.

Question 220

How does water affect oil properties?

Answer 220

Water can change oil’s viscosity, lubricity, and load carrying characteristics.

Question 221

What chemical reaction does water cause in lubrication systems?

Answer 221

Water causes additive depletion, leading to oxidation due to the formation of acids.

Question 222

What is the main cause of oxidation in lubrication systems?

Answer 222

The main cause of oxidation is heat.

Question 223

List the three products of oxidation.

Answer 223

• Gum and varnish
• Sludge
• Acids

Question 224

What harm does gum and varnish caused by oxidation cause to an oil system?

Answer 224

Sticky valves

Question 225

What harm does slude caused by oxidization cause to an oil system?

Answer 225

Blocked pilot passages

Question 226

What harm do acids caused by oxidization cause to an oil system?

Answer 226

Corrosion of parts

Question 227

What four things does routine oil analysis identify?

Answer 227

1. metallic particles
2. contaminants
3. oxidation
4. water content.

Question 228

How does routine oil analysis assist with predictive maintenance?

Answer 228

It helps to determine how often the oil should be changed.

Question 229

Water in oil can change what three oil characteristics?

Answer 229

1. viscosity
2. lubricity
3. load carrying characteristics

Question 230

True or False: Overheating the lubrication system can damage fluid or system components.

Answer 230

True

Question 231

When taking an oil sample from a machine, it should be taken from a ____ zone.

Answer 231

live zone

This is for circulating (pumped) oil systems.

This is an area where in the ciculating oil has aquate turbulent flow to ensure that the oil is propelry mixed.

Question 232

True or false: When taking an oil sample for analysis, the sample should only be collected when the machine is running at its normal operating temeprature, pressure, speed, and load.

Answer 232

True

You want the sample to be the most accurate representation of the oil flowing through the machine.

Question 233

When collecting oil samples, the sample should be taken 1.________ (upstream/downstream) from system components and 2.________ (upstream/downstream) from fitlers or separators.

Answer 233

1. downstream (after)
2. upstream (ahead)

Question 234

True or false: Do not collect oil samples at points located at dead pipe legs where the fluid is not moving or after filters or separators.

Answer 234

True

This would be an inaccurate representation of the oil in service.

Question 235

How is contamination measured in oil analysis’?

Answer 235

By particle size and the number of particles of a particular size

Question 236

What are the three micron size of particles measured using ISO cleanliness standards?

Answer 236

4µ, 6µ, and 14µ

µ = micron ⟶ one millionth of a metre (micrometre)

Question 237

True or false: All objects, even cold ones, emit infrared radiadion.

Answer 237

True

The warmer the object, the more radiation is emitted.

Question 238

What is a thermogram?

Answer 238

an image that represents the distribution of surface temperatures of an object or area

These are captured with thermal imaging camera.

Question 239

As it related to thermal imaging, what is emissivity of a material?

Answer 239

A materials ability to emit radiation.

Question 240

What is thermal emissivity tape used for with IR scans?

Answer 240

To calibrate the camera.

The tape has a known and consistent thermal emissivity that is used as a baseline.

Question 241

What effect does reflection have on IR scans?

Answer 241

Inaccurate readings

Adjusting the angle of the camera so that reflection is not an issue eleminates this issue.

Question 242

A thermal imaging camera produces an image called a:

Answer 242

thermogram

Question 243

What contaminant can cause additive depletion and create oxidation of lubricating oils?

Answer 243

water