Noise & Vibration Control MCQ
What is the definition of Probabilistic Vibration?
Answer
Correct Answer:
Vibration with a magnitude that can only be predicted on a statistical basis.
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What is the magnitude of probabilistic vibration?
Answer
Correct Answer:
Cannot be predicted on a statistical basis
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What is the meaning of "platform" in MIL-STD-810?
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Correct Answer:
Any vehicle, surface, or medium that carries a piece of equipment.
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What is a platform?
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Correct Answer:
Any vehicle, surface, or medium that carries a piece of equipment
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What is a piezoresistive transducer?
Answer
Correct Answer:
A transducer with an electrical output that depends on the deformation of its semiconductor resistive element
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Which of the following is true about a piezoresistive transducer?
Answer
Correct Answer:
It offers greater resistance to change than the wire of a strain-gauge transducer for a given deformation.
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What is the fractional part of a period called?
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Which of the following is a characteristic of performance-based requirements?
Answer
Correct Answer:
They describe what the product should do.
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What is a patent defect?
Answer
Correct Answer:
A flaw in and/or the workmanship of a part or assembly that has failed under a test or screen.
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What is an orbit?
Answer
Correct Answer:
The path of a shaft centerline during rotation
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What is a precomputed drive signal in open-loop control?
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Correct Answer:
A signal that is computed before it is sent to the system.
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What is Open-loop control?
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Correct Answer:
Precomputed or preconceived drive signals without modifying or refining the signals based on observation of the resulting motion.
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What is the control of a computer's data sampling rate called?
Answer
Correct Answer:
Order tracking
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What does operational limit refer to?
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Correct Answer:
The extremes beyond which a product is not expected to operate.
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What is an octave?
Answer
Correct Answer:
The interval between two frequencies differing by exactly 2:1
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What is the interval between two frequencies differing by exactly 2:1 called?
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What is the definition for nonlinearity?
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Correct Answer:
The deviation from a best fit straight line of the true output versus the actual value measured.
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What is an undamped system's natural frequency also known as?
Answer
Correct Answer:
The frequency of the normal modes of vibration.
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What is the natural frequency of an undamped system's free vibration?
Answer
Correct Answer:
It is the frequency of the system's normal modes of vibration.
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What is the purpose of notching?
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Correct Answer:
To prevent unnecessary excitation of any large resonances that may occur during a vibration test.
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What is the noise floor?
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Correct Answer:
The summation of all noise sources and unwanted signals within a measurement system.
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What is the definition of natural environment?
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Correct Answer:
Conditions that occur in nature and are not caused by equipment
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What is a mission profile?
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Correct Answer:
Time-phased description of the events and environments an item experiences from initiation to completion of a specified mission.
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One micron is equal to _______.
Answer
Correct Answer:
10-6 meters
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How many microns are in one inch?
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What is mechanical failure?
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Correct Answer:
A malfunction consisting of cracking, excessive displacement, misalignment, loosening, etc.
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What is the mean?
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Correct Answer:
A value intermediate between quantities under consideration
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What is Machinery health monitoring?
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Correct Answer:
The measurement, recording, and analysis of machinery parameters to determine machinery health.
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What is the other name for lateral sensitivity?
Answer
Correct Answer:
Cross-axis sensitivity
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What is Lateral sensitivity?
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Correct Answer:
Sensitivity of a sensor in a direction perpendicular to the sensitive axis.
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What is liquid nitrogen's chemical formula?
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What is a life unit?
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Correct Answer:
A measurement of an item's use duration
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What does the life unit measurement include?
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Correct Answer:
Time, cycles, distance, rounds fired, attempts to operate, etc.
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The logarithm is normally base ____.
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What is a latent defect?
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Correct Answer:
A flaw in a part, assembly, and/or workmanship that is dormant but can result in failure.
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What is a keyphasor?
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Correct Answer:
A signal generated by a sensor that observes a once-per-revolution event
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What is the rate of change of acceleration with time called?
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What does intensity measure?
Answer
Correct Answer:
The severity of vibration or shock
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What is the input impedance?
Answer
Correct Answer:
Shunt resistance and capacitance/inductance measured at the input terminals
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What is another term for "inertially-referenced motion"?
Answer
Correct Answer:
Free space
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A sensor that measures motion referenced to a fixed point in space is what?
Answer
Correct Answer:
Inertially-referenced
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What is an impulse?
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Correct Answer:
The integral of force over a time interval.
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What is the cause of imbalance?
Answer
Correct Answer:
The unequal distribution of weight or mass on a rotor
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What is the unequal distribution of weight or mass on a rotor called?
Answer
Correct Answer:
Imbalance
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What is hash?
Answer
Correct Answer:
A distortion in a signal
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What is a hard failure?
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Correct Answer:
When a product under test ceases to work correctly and does not resume correct operation.
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What does a haversine pulse look like?
Answer
Correct Answer:
A sine wave
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What is harmonic distortion?
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Correct Answer:
A distortion in an output signal caused by the presence of frequencies not present in the input signal
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What does HALT stand for?
Answer
Correct Answer:
Highly Accelerated Life Test
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What does the acronym HALT stand for?
Answer
Correct Answer:
Highly accelerated life tests
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What is the value for 1 gravitational unit?
Answer
Correct Answer:
9.80665 m/s²
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How many gals are equivalent to 1g?
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What is the acceleration represented by the unit gal?
Answer
Correct Answer:
1 cm/sec²
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What is the main cause of a ground loop?
Answer
Correct Answer:
Voltage drops between the two ground connections
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What are ground loops caused by?
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Correct Answer:
A signal source and a signal measurement device being grounded at two separate points on a ground bus.
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What does graduation mark mean?
Answer
Correct Answer:
The scale intervals on a measuring instrument
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What does the PSD measure?
Answer
Correct Answer:
The signal is measured in acceleration using the gravitational constant G.
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What are the units of PSD?
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What is FEA?
Answer
Correct Answer:
A computer-aided design technique for predicting the dynamic behavior of a mechanical system.
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What does the definition of MTBF stand for?
Answer
Correct Answer:
Mean Time Between Failures
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What is the definition of failure?
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Correct Answer:
Failure is the event or inoperable state in which any item or component does not perform as previously specified.
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What is the goal of environmental stress screening?
Answer
Correct Answer:
Precipitate latent defects into recognizable failures
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When is an eddy current generated?
Answer
Correct Answer:
When a conductive material intercepts the electromagnetic field of a displacement or proximity probe
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What are equal loudness curves?
Answer
Correct Answer:
Graphs of pure tone sound pressure levels versus frequency.
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What is the meaning of the word "environment"?
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Correct Answer:
The aggregate of all external and internal conditions that influence the form, performance, reliability, or survival of an item.
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What is environment defined as?
Answer
Correct Answer:
An aggregate of all external and internal conditions that influence the form, performance, reliability, or survival of an item.
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What is mechanical eccentricity?
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Correct Answer:
A variation of the shaft surface radius when referenced to the shaft’s true geometric centerline.
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What is distortion in electronics?
Answer
Correct Answer:
Any unwanted signal
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In which field is distortion defined as any unwanted signal?
Answer
Correct Answer:
Electronics
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What is accomplished by multiplying the velocity signal by jΩ in a computer?
Answer
Correct Answer:
Representation in terms of time rate of change.
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What does differentiating velocity yields?
Answer
Correct Answer:
Acceleration
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What is the number of DOF?
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Correct Answer:
The number of values in the final calculation of a statistic that are free to vary.
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What is the number of directions of motion on a structure?
Answer
Correct Answer:
Degrees of freedom
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What is the main purpose of damping?
Answer
Correct Answer:
To dissipate oscillatory or vibratory energy
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What is the definition of damping?
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Correct Answer:
The dissipation of oscillatory or vibratory energy with motion or with time.
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What is a digital-to-analog converter?
Answer
Correct Answer:
A device that converts a digital signal into an analog voltage
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What is the reciprocal of stiffness?
Answer
Correct Answer:
Compliance
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What does compliance describe?
Answer
Correct Answer:
Displacement divided by force
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What is the purpose of closed-loop control?
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Correct Answer:
To refine or modify drive signals to bring responses closer to desired motions.
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What is chatter?
Answer
Correct Answer:
An event that can occur in response to shock vibration
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What is a sensor?
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Correct Answer:
A device that converts a physical quantity, such as light intensity or pressure, into an electrical signal
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What does calibration mean?
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Correct Answer:
The process of adjusting the measured voltage and frequency readings based on a precise internal reference voltage.
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What is the primary purpose of a barrier?
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Correct Answer:
To block airborne sound from entering the passenger compartment
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What is the purpose of a bounce test?
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Correct Answer:
To assess the effect of vibration on unrestrained cargo
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What does bias refer to?
Answer
Correct Answer:
A more or less persistent tendency for a group of measurements to be too large or too small.
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What is the unit of measurement for bandwidth?
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What is a sound exemplified by loose power transformer laminations?
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What is the power frequency in Hz of a sound exemplified by loose power transformer laminations?
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What is the definition of broadband?
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Correct Answer:
Vibration or other signals that are unfiltered.
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What does broadband refer to?
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Correct Answer:
Signals at all frequencies contribute to the measured value.
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What does a bode plot display?
Answer
Correct Answer:
Magnitude of vibration at 1x the shaft speed and its phase relative to the shaft position
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What is a bode plot?
Answer
Correct Answer:
A graph of magnitude and phase plotted against speed.
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What is a baseline spectrum?
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Correct Answer:
A vibration spectrum that is recorded when a machine is in good working condition.
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What is the term for the process of adjusting the distribution of mass in a rotating element to reduce vibratory forces generated by rotation?
Answer
Correct Answer:
Balancing
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What is balancing?
Answer
Correct Answer:
The process of adjusting the distribution of mass in a rotating element to reduce vibratory forces generated by rotation.
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What is the meaning of "Axial?"
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Correct Answer:
The direction along the centerline of a shaft.
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What is the average value of a pure sine wave?
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What does a power spectral density plot show?
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Correct Answer:
A spectral display of the power (voltage squared) at each frequency.
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What does an anti-aliasing filter do?
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Correct Answer:
It stops frequencies higher than some fraction of the sample rate to minimize aliasing.
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What is an anti-aliasing filter?
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Correct Answer:
A low-pass filter designed to stop frequencies higher than some fraction of the sample rate to minimize aliasing.
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What does Amplitude refer to?
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Correct Answer:
Displacement, velocity, acceleration, voltage, current, force, or pressure.
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What is amplitude?
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Correct Answer:
The magnitude of a quantity's variation from its zero value
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What causes aliasing in a spectrum?
Answer
Correct Answer:
Sampling data at too low a sampling frequency
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What is aliasing?
Answer
Correct Answer:
A spectrum analysis problem that results from sampling data at too low a sampling frequency.
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What is accessibility?
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Correct Answer:
Accessibility measures the related ease of access to various portions of an item for operation or maintenance.
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Accessibility is the related ease of what to various portions of an item?
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What is accelerated stress testing?
Answer
Correct Answer:
A post-production process on a sample of units to precipitate hidden or latent failures.
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What is the main purpose of accelerated stress testing?
Answer
Correct Answer:
To precipitation hidden or latent failures.
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Seismic sensors measure _____ vibration.
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What is absolute vibration?
Answer
Correct Answer:
Vibration of an object relative to a fixed point in space.
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What changes an analog signal into a digital signal?
Answer
Correct Answer:
A digital converter
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What is an analog signal?
Answer
Correct Answer:
A signal that changes in voltage or current
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What is the process of summing and dividing several like measurements to improve accuracy or lessen the effect of any asynchronous components called?
Answer
Correct Answer:
Averaging
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What is the degree to which an item is in an operable and committable state at the start of a mission called?
Answer
Correct Answer:
Availability
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What does an angular rate sensor measure?
Answer
Correct Answer:
Rotational velocity (degrees or radians per second) around its sensitive axis.
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What is the ambient environment?
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Correct Answer:
The conditions that characterize the air or other medium that surrounds the material.
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What is the purpose of an aggravated test?
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Correct Answer:
To reduce test time or assure a margin of safety.
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What is an accelerometer?
Answer
Correct Answer:
A sensor, transducer, or pickup that converts acceleration into an electrical signal.
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What are the two common types of accelerometers?
Answer
Correct Answer:
Piezoresistive and Piezoelectric
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What is the purpose of accelerated life testing?
Answer
Correct Answer:
To identify failure-prone, marginally strong elements by causing them to fail.
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What is the meaning of traceable to NJST?
Answer
Correct Answer:
A measure of the uncertainty of an instrument reading compared to that of a primary standard
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What is the goal of equalization?
Answer
Correct Answer:
To compensate for the non-flat frequency response of human hearing
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What is the axial position?
Answer
Correct Answer:
The change in a rotor's position or displacement along its axis and relative to a fixed point nearby.
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What is another name for average responding?
Answer
Correct Answer:
Mean responding
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What is the average responding proportional to?
Answer
Correct Answer:
The average of the absolute values of all input waveforms
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Auto-ranging is the capability of an instrument to switch ranges automatically. True or False?
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What does auto-ranging refer to?
Answer
Correct Answer:
The capability of an instrument to switch ranges automatically.
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What is the square root of the area under the ASD curve defined as?
Answer
Correct Answer:
G RMS of acceleration
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What does ASD stand for?
Answer
Correct Answer:
Spectral Density
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What is the frequency in Hz of a 10 rad/s angular frequency?
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What is the torsional vibration frequency in radians per second?
Answer
Correct Answer:
Angular frequency
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Which of the following is NOT a desired machinery condition of alignment?
Answer
Correct Answer:
Least vibration
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What is the desired machinery condition when the axes of a machine's components are adjusted to be colinear, parallel or perpendicular?
Answer
Correct Answer:
Alignment
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What is the relationship between accuracy and inaccuracy?
Answer
Correct Answer:
Accuracy is not related to inaccuracy.
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What is acceleration?
Answer
Correct Answer:
The rate of change of velocity with time
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What is the rate of change of velocity with time called?
Answer
Correct Answer:
Acceleration
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How does an absorber work?
Answer
Correct Answer:
By converting vibration to heat
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What is an absorber?
Answer
Correct Answer:
A device capable of reducing or attenuating vibration
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What does the term "absolute" refer to in calibration?
Answer
Correct Answer:
Calibration based on the primary standards of mass, length, and time
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How do 6DOF machines produce vibration?
Answer
Correct Answer:
They use air-driven impact hammers to excite a vibrating plate or table
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